Rocky Mountain Audio Fest – Friday, Part 2

The crowds were lighter than I expected on Friday. As a result, I covered more ground than expected, but with each room, my notes and publishing backlog grew. I’m expecting today to be actually busy, so that should give me time to catch up a little. The day was full of surprises, there were a few rooms that I was expecting to sound great that, sadly, didn’t (you won’t be hearing about those from me, Mom said, “if you can’t say something nice, don’t say anything at all”). There were others that I thought would be decent but ended up being completely delightful. There were products that I didn’t know existed that are now on my “must evaluate” list–a few both personally and professionally.

ESS AMT™ 12″ loudspeakers

ESS is no stranger to anyone in this industry. Their innovative Heil Air-Motion Transformer™ was impressive when it appeared on the scene 45 or so years ago, but what most people don’t know is that, after a thirteen-year hiatus, ESS is back and continuing to innovate under the leadership of Ricky Caudillo. His new products have better cabinets, treated paper cone woofers, and he says that they don’t require topflight amplification to sound great. I was impressed by what I heard and look forward to revisiting room 538 later this weekend.

isoACOUSTICS GAIA isolation for Speakers & Subwoofers

I didn’t quite know what to expect when I walked into Paul Morrison’s room (8013)…why two pairs of loudspeakers and subs at different heights? After a brief demo, it all made a lot more sense. The left two speakers are simply spiked to the carpet using manufacturer provided supports while the right pair is supported using isoACOUSTICS isolation system. Same goes for the subs. The result was a surprising increase in soundstage width, depth. The explanation is that without isolation, energy reflects from the floor back into the loudspeaker cabinets, causing the soundstage to collapse a bit. Like lowering the noise floor in your listening room, the impact of these reflections is something that you won’t notice until they are gone. Fascinating!

Stunning Paradigm Persona Loudspeakers

The Paradigm room (9007) was graced with their Persona loudspeakers that really do sound as good as they look. The top end is airy and lite and should complement most listening rooms well, although all of that energy up top could be a little much for rooms lacking carpeted surfaces and diffusive surfaces. I’m looking forward to giving them another listen today.

Rocky Mountain Audio Fest – Friday

I tried to take the best advantage of the two-hour headstart afforded to members of the press on the first day, but despite my best efforts, only visited half of the rooms on my list. The layout is good this year with most exhibits in the tower. The stairwells are unlocked, so one can take the elevator to the 11th floor and then work their way down via the stairs without waiting on the lift.

It’s way to early to even be thinking about best-sound-of-show, but Paul McGowan’s room, featuring Focal loudspeakers and his new P20 power regenerator was delivering some of the best sound that I’ve heard anywhere.

PS Audio  in the Spruce room – BTW, that’s Principal designer, Ted Smith in the background

Legacy Audio’s much-anticipated VALOR loudspeaker was ready to play when I stopped by first thing this morning.

Legacy Audio VALOR in the Evergreen A room

At the time, Bill was putting the finishing touches on room correction for the CALIBRE stand mount loudspeakers which were clearly punching far above their weight!

Legacy Audio CALIBRE in the Evergreen A room

The Wyred 4 Sound room sports their new statement nextGEN amplifier driving a premier appearance of the Acoustic Zen Maestro loudspeakers. The combination thrilled playing Drum Improvisation by Jim Keltner.

Wyred 4 Sound in Spruce 2 with Acoustic Zen loudspeakers

Much more to come!

Rocky Mountain Audio Fest – Thursday

Before the Show

I’ve been an audiophile for thirty years, but weirdly, this is my first time traveling to Denver for the Rocky Mountain Audio Fest. It’s a little intimidating with 400 or so companies displaying products in over 160 exhibits and an expected attendance north of 3,500. It’s impractical to thoroughly explore even half of what’s here in just three days, so I’ve got to do some serious pre-show planning this evening. After scanning press releases that many of the attending manufacturers have issued during the weeks leading up to the show, I’ve observed some interesting trends that may affect how I choose to allocate time.


snapshot from my window seat as we approached the area

The Stereo Receiver Reimagined

As a component, the traditional integrated amp has been mutating, and this year’s RMAF may reveal where evolution has taken it. It all makes sense when you think of it. You start with a basic integrated amp—source selection and amplification with attenuation and a second gain stage between them. Many include a built-in phono stage, so add a DAC and some digital inputs and now you have an integrated amp that supports both analog and digital sources. But, why stop there? Add a small board computer with the right software, and it becomes a Roon output with support for local and Internet streaming. Add all of these changes up, and what have we got? Something that looks rather like that stereo receiver that you had back in the ‘80s before home theater appeared on the scene and made everything more complicated.

Manufacturers who have recently announced or are introducing evolved stereo receiver like products at RMAF this year include:

  • AVM – OVATION CS 8.2 All-In-One System
  • Technics – SC-C70Premium Ottava All-In-One Audio System
  • Peachtree Audio – decco125 SKY
  • DEQX – HDP-5

I’m looking forward to checking all of these out over the next three days.

Serious Emphasis on Personal Listening

I’ll go into more detail as the week progresses, but all five of the budget system rooms this year include two systems…one based on loudspeakers and a second based on headphones…almost begging participants to compare performance at their given price point. There’s the onsite CANJAM, of course, but also silent listening rooms that are set up with only headphone systems. Mojo Audio is here with dedicated headphone rigs in the $20k to $40k range. Yikes!

Raspberry Pi 3 for Roon Bridge

Roon is an amazing piece of software for organizing your local digital music collection and seamlessly expanding your library via streaming selections from TIDAL. The v1.3 update of Roon has been covered well on many sites so I won’t dig into it here, but DSP and convolution plus third party integrations shift Roon into the Must Have category for the modern audiophile.

What Roon actually does has been covered thoroughly on other sites as well. If you have not tried it, I encourage you to take advantage of Roonlabs’ free trial. However, keep in mind that if you only run it on your laptop or desktop PC, you’re not getting the full picture…not even close! No…to really make Roon sing in your HiFi setup, you’re going to need at least two computers, a laptop, a tablet or smartphone, and a local wired + wifi network to tie this all together. It sounds complicated, but I promise that you don’t need a computer science degree or thousands of dollars to build a system that sounds better than you thought it could and is an absolute joy to use.

Although you can run the full Roon stack on a single PC, you’ll get better performance and convenience by running each component on its own dedicated device. I’ll explain why in a bit, but here are the components:

  • Core (Roon Server) – a backend process (no UI) that acts as the communications hub for Roon. It does all of the heavy-lifting, including indexing your music library, communicating with 3rd party services like TIDAL and, downloading enhanced metadata, upsampling, convolution, and other DSP tasks, and managing devices and zones.
  • Output (Roon Bridge or Roon Ready Devices) – a physical (“Roon Ready”) component or backend process (no UI) running on a dedicated computer that routes audio streams from Roon Server to one or more local devices (eg, an attached DAC or speaker)
  • Control (Roon or Roon Remote) – the graphical UI that you interact with to find what you want to hear and play it. Also used to manage settings for each zone/device

And here are some of the problems with running all of Roon’s components on a single computer:

  • Noise – Laptops and desktops are mechanically and electrically noisy devices. Some are better than others, but just about every computer with decent performance uses one or more fans to stay cool. Some also have mechanical hard disk drives that add mechanical vibrations to the soundtrack. Lots of other internal circuitry make for a very electrically noisy environment. This is not something that you want to have in your listening room if you are seeking high-performance playback. It’s certainly not something that you want to have directly connected to or otherwise sharing the ground plane with your audio gear.
  • Convenience – An app running on your smartphone or tablet is a more convenient way to control what’s playing than walking over to the PC or awkwardly fiddling with a laptop that has a 5m cable attached to it. You can control what music is playing in every zone of your house simply by reaching into your pocket and pulling out your smartphone. Queue up an album or two for playback in the main listening room, set your tablet or phone face down, and enjoy playback without distractions.
  • Quality – This falls under the category of your mileage may vary; however, at least in theory, feeding a USB DAC from a computer with very low CPU utilization usually results in better sound. Possible reasons for this include less USB jitter, lower DPC latency, and less electrical noise entering the DAC. A general purpose computer (eg., running MS Windows or Apple OS X) has many hundreds of background threads running to keep the system responsive to all of its inputs, to keep software updated and safe from security issues, and so on. All of these background tasks keep the CPU occupied while you would prefer for it to be 100% dedicated to feeding the DAC.

The traditional way to address the Quality/CPU utilization issue is to use a powerful server with many high-speed CPU cores that can handle the background tasks with minimal effect on latency. However, unless this system also employs liquid cooling, it will be noisy, so we’ve traded one problem for another!

A second approach is to run audio specific optimizers or system tuners which disable most background tasks that are not required for music playback. This is a compromise approach that trades some usability for some improved streaming performance and is commonly employed on PCs that can serve as dedicated as media players.

However, as I have suggested, there is a better way: instead of running the media player on one computer, use multiple devices, each optimized for its task.

The device that you attach to your DAC in the listening room must be fanless, solid-state, and completely silent. This typically necessitates using a smaller, low power device, but that’s fine because its only task is to stream digital audio from a LAN connection to an attached USB or S/PDIF DAC. This device ideally behaves like an appliance…connect Ethernet, power, and a digital output cable and it just runs. It should have few configuration options and it should not be burdened with upsampling or DSP tasks. A device in this category is sometimes referred to as a NAA (Network Audio Adapter). Examples include the Sonicorbiter and microRendu from Sonore, but solid-state fanless PCs from Logic Supply, Azulle, and Minix are popular alternatives that, when combined with and OS tuners like Audiophile Optimizer or Fidelizer Pro, can produce acceptable results.

A relatively new entry into the NAA category is the humble Raspberry Pi single board computer (SBC). The Sonore products are actually based on similar technology, but until recently, getting reliable streaming performance from these inexpensive, low power devices required hours of DYI tinkering and Linux wizardry. Thankfully, the following developments have made a once difficult process trivial:

  • The Raspberry Pi foundation released the Pi 3 Model B in early 2016 (64-bit CPU with 33% faster clock and 50% faster memory bus than its predecessor)
  • Roonlabs released Roon Bridge for the Raspberry Pi shortly after
  • DietPi added Roon Bridge to their software installer in late 2016

With these developments, the tedious process of getting excellent sound via this $35 device has been reduced to a set of simple steps that just about anyone with minimal computer skills can follow. I recommend ordering a model that includes heat sinks like the B01KGMMI1A. It comes in a nice little sandwich bag:

Your choice of case and heatsinks depends on if you intend to add one of the HiFiBerry DAC Hats to the device. If you are content with only USB connectivity, the high profile heatsinks I have recommended will keep the device cooler, and the official Raspberry Pi 3 case for $7.75 will do just fine. Peel off the backing from the heatsinks and put them on the two chips of the same size, then snap the Pi 3 board into the case. Assembly is complete. If you’ve ever built your own PC, this process is bizarrely simple!

Before you can boot the Pi, you need to download the DietPi OS image and load it onto a microSD card. This will require another computer, and the process that you follow will depend on what OS that computer is running (Windows, Mac OS X, or Linux). Select the Raspberry Pi from the Download page on the DietPi site. Unlike other Pi distros that are 1GB or more, The DietPi image is under 100MB, so it should download quickly. You can find instructions for copying the image to your card on the official Raspberry Pi site. Although these instructions are for Raspian (the official OS for the Pi), they will work just fine for DietPi:

Eject the microSD card from your computer, remove it from the SD adapter, and carefully slide it into the small slot on the bottom of the Pi 3. The contacts on the card face towards the underside of the Pi’s board. With the Pi now fully assembled, connect it to a spare HDMI input on your TV or computer monitor. Connect a USB keyboard to one of the four USB ports and run a patch cord from the Ethernet jack to your switch or router. Finally, connect a beefy cell phone charger (5V, 2A minimum) to the micro USB port. If your TV is set to the correct input, you’ll be greeted with some boot messages:

The Pi will go through a couple of cycles of updating itself after you login, and then you’ll be presented with a simple setup menu. Accept all of the defaults, but go to the “Software Optimized” section and enable “Roon Bridge” under “Media Systems”.


If you don’t see this, run dietpi-software:

After another reboot, connect your DAC and your new Roon output should be ready to go. If you have not already done so, install Roon Server on another computer or laptop that’s on the same network. Ideally, this will be a computer that you can leave on all of the time. If you don’t have something like this, consider one of the small fanless PCs that I listed above, but be sure to select one that runs a 64-bit OS.

With Roon Bridge and Roon Server up and running on your network, all that remains is to install Roon or Roon Remote on a device that you can use to control the environment. I recommend installing Roon on a laptop to perform the setup since there are still a few options (like DSP) that are not available on all versions of the Roon Remote tablet/smartphone apps. Once you have the UI running, you’ll be asked to select a zone. Scroll down a bit, and you should see your Raspberry Pi (listed as “DietPi … Linux 4.x”) with one or more devices associated with it:

If you don’t see your DAC listed, try unplugging it and plugging it back in. Use the gears to adjust settings and be sure to give it a name that will help you to identify it. Although I did not do so in this example, it’s a good idea to include the room name in the name you assign to the zone. You may eventually have a bunch of Roon zones, so knowing which room they are in will help keep things easy to use for other family members. 🙂

I’ve found that the little Raspberry Pi Model 3 can keep up with pretty much any DAC. I had no trouble streaming native DSD128 and 352.8kHz PCM:

What’s so great about this setup, again, is that the PC running Roon Server handles all of the CPU intensive work. As you see below, I have the more powerful server PC (an HP Stream mini in my case) applying room correction filters that I generated using Acourate before streaming the results to the tiny Raspberry Pi in the listening room. CPU usage on the Pi is no greater than it would be if I was playing this album without DSP. Separating these functions provides all of the benefits from DSP with none of the noise and jitter downsides. Interacting with the system is a simple matter of reaching for a smartphone or tablet.

If any of this sounds interesting, you may be wondering specifically what bits you would need to set up something similar in your listening room. The most difficult part for most audiophiles is running a wired Ethernet connection. While the Raspberry Pi 3 Model B does have support for wifi, I have not tested it and generally find that a wired connection is faster and more reliable. Unless you really have no choice, save yourself the headaches and have an Ethernet cable run or an Ethernet jack installed.

To set up the system that I have described, you’ll need an external USB DAC that you can connect to the Pi. If you’d like to use your existing DAC but it only has an S/PDIF input, consider adding a HiFiBerry Digi+ Pro card. This $45 accessory just snaps onto the top of the Pi’s main board and adds high-quality COAX and TOSLINK S/PDIF outputs with dedicated clocks. If you don’t yet own a DAC, and you’re not sure that you want to make the investment now, the HiFiBerry DAC+ Pro is a great option with ridiculously good performance for its tiny $45 price. Again, dedicated clocks make the “Pro” model well worth the extra few bucks vs. the other models.

If you have nothing in your (intended) listening room except for electricity, an Internet connection, and a chair, here’s a sample system that I put together to help you get started:

Best Roon + TIDAL + HiFiBerry System for under $1k

Feel free to exclude parts that you already have or swap out parts based on personal preference, but this should give anyone a decent place to start.

I keep saying it, but this is a really great time to be involved with the audio hobby. Thanks to recent advancements in streaming technology (TIDAL + MQA), distributed media player software (Roon), and digital room correction (Acourate), and small, inexpensive computers (Raspberry Pi 3 Model B) it’s possible to build an audio system that, with meticulous setup, has the potential to outperform traditional HiFi systems which cost many times more. This same digital technology can also help take your existing system to the next level of performance and convenience with minimal expense and effort.

If there’s anything that I can do to help you get setup, don’t hesitate to ping me. I’m “dsnyder0cnn” at Cheers and happy listening!

HOWTO: Streaming TIDAL via JRiver Media Center

I’m so excited! I just have to share…even though chances are slim that you will have any need for a setup like this. Before I get started, let me first explain my situation and why I’m excited.

I have large loudspeakers in a small room, so to get the bass under control, my system really needed some help from a digital room correction system. After much research, I chose Acourate from AudioVero to design a target response curve and build FIR filters. See my previous blog post for details. The final step was to configure the convolution engine within JRiver Media Center to apply these filters during playback.

This system sounds great (to me, at least), and the JRemote tablet interface works really well. However, there are a few issues with this setup:

  • Real-time convolution means playback controls have a few seconds of extra lag
  • Playback is limited to PCM files (no DSD)
  • No TIDAL HiFi Streaming

The first two are no big deal; I generally listen to entire albums or playlists, so lag is a non-issue once the music starts. I also only have a tiny handful of DSD tracks which, if I cared, could be converted to high-rez PCM files. However, that last issue–no TIDAL streaming–has been a major bummer! When someone suggests new music, I can login to TIDAL and preview it on my laptop but hearing what it really sounds like in the Loft must wait until I buy the CD or download it from HDtracks. When a friend drops by for a listening session without a thumb drive containing their favorite reference tracks, they are stuck wandering aimlessly through my collection. Not cool.

Until now, my only hope has been for a TIDAL player like roon to add a convolution feature or for JRiver to add support for TIDAL streaming. Sadly, neither of these things are likely to happen anytime soon. Other alternatives like feeding JRiver’s WDM or ASIO driver from a local TIDAL streamer proved unreliable at best. I’ve spent more hours than I care to admit trying to get TIDAL lossless streaming and digital room correction working together in the Loft.

My breakthrough came this evening when I started thinking about Signalyst’s Network Audio Adapter architecture:


Ignoring room correction convolution for a moment, JRiver acts like the “FIFO”, streaming digital music data from my Synology NAS to my DAC, so the question was, “Is there a way to stream TIDAL to JRiver?” Thankfully, the answer was yes! JRiver can be configured as a DLNA Renderer. This is just a fancy “DLNA” way of saying that JRiver can be streamed to and controlled by an external media player. All I had to do was find a TIDAL player that could act as a DLNA server/controller and I’d be set.

The answer was an Android smartphone/tablet app called BubbleUPnP UPnP/DLNA. I had avoided DLNA in the past since I imagined that using it would somehow compromise sound quality; however, once I got things configured correctly, I have yet to notice any loss in quality.

The first step was configuring JRiver to act as a DLNA renderer. If you have enabled the “Media Network” feature of JRiver (necessary for JRemote control), chances are that the DLNA renderer is already enabled, but confirm by opening settings and looking here:



Next, locate BubbleUPnP in the Google Play Store and install it on a compatible Android tablet or smartphone. Although the free version has worked for my testing, I’ll almost certainly spring for the $4.69 version to remove ads and playlist limitations.

Configuration of BubbleUPnP is just three steps:

  1. Select the Renderer (in our case, JRiver)
  2. Select the Library (TIDAL)
  3. Configure TIDAL for lossless streaming

In my case, selecting the Renderer looked like this (I chose “LOFT: ifi micro iDAC2” with the JRiver icon):


BubbleUPnP can optionally display the properties of the renderer, including supported formats:


Note that while FLAC is listed, there’s no DSD…and even if there was, the convolution engine does not support it.

You’ll find TIDAL under “Cloud” in the “Library” setup section. The first time through, you’ll be asked for your TIDAL username and password:


Before you play anything, you’ll want to make sure that TIDAL is configured to deliver the highest quality stream. By default, it’s 96kbps lossy compression…not good. To fix this, go to:

“Settings” -> “Settings” -> “Local and Cloud” -> “cloud content” -> “TIDAL”

…and make sure that “FLAC” is selected for both “Wifi/Eth audio quality” and “Mobile audio quality”.


Now you’re ready to go back to “Library” -> “Cloud” -> “TIDAL” and find some music. The TIDAL interface inside of BubbleUPnP is neither beautiful or sophisticated, but what functionality is there works well. Use the big magnifying glass at the top of the interface to search for some music. Depending on what you enter, you’ll get back a few folders on the screen that represent albums, artists, and tracks that matched what you entered. If it was an artist, pick the “Artists” folder…where hopefully, you’ll find the artist you were looking for near the top of the list. After making your selection, you’ll find more folders representing albums, top tracks, radio, etc. I usually head straight to “Albums” and then queue up what I’m looing for from there. For example:


A few seconds after initiating playback from BubbleUPnP, you should see/hear playback starting on JRiver. You can even verify this using JRemote, which shows the album art and some of the track metadata:


The thing to look for here is the “FLAC” indicator at the bottom of the screen. This is confirmation that JRiver’s DLNA Renderer is getting a lossless stream from TIDAL by way of BubbleUPnP. The “Info” button on JRemote provides more interesting details. For example:

track_metadata_1 track_metadata_2

Note that you can optionally use JRemote to pause/stop playback and skip forward/back within the track that’s currently playing. However, JRiver will only “see” one track at a time in the playlist. Also, I found that I can’t resume playback from within JRemote after I stop it; I have to go back to BubbleUPnP to resume. I can do that from either the “Playlist” or “Now Playing” views in BubbleUPnP.

I have not spent much time doing direct comparisons between local FLAC and FLAC streams of the same albums from TIDAL, but this setup really sounds great. I seriously doubt that I could tell them apart when TIDAL has the same master and release. This setup has worked flawlessly with the convolution engine within JRiver that I depend on for room correction, and although the TIDAL interface is a little clunky, once an album is queued up, I forget all about that and just enjoy the music!

This has been a major breakthrough for me since it enables lossless TIDAL streaming while applying Acourate room correction filters in our main listening room. If this had not worked, I was heading down the path of buying a microRendu, roon, and HQPlayer plus a more powerful desktop PC to run the processing…or perhaps considering the Aurender route…a few thousand bucks either way. Now it seems that I don’t have to. 🙂

Even if your use case is less complex, I hope you find some way to take advantage of a setup like this. Cheers and happy listening!

Update: If you don’t have an Android smartphone or tablet handy, it may be possible to do the same thing that I have described above on Apple IOS devices using mconnect player. If I get around to testing this, I’ll post any setup gotchas here.

Another interesting use case for this JRiver DLNA Renderer setup is enabling guests to stream music from their mobile devices to your playback system without having to resort to Bluetooth. All they would have to do is install the free version of BubbleUPnP or mconnect player.

2nd Update: I’ve expanded a bit more on the ideas behind this setup on the Morrow Cables Forum. Here’s a link: Can Streaming Sound Better than CD?

3rd Update: Gapless playback with BubbleUPnP + JRiver! Yes, that’s right. Just enable “Enable gapless control” under the “UPnP Tweaks” menu in BubbleUPnP Settings:

Enable gapless control

In spite of the warning, this setting works beautifully in JRiver. With this setting enabled, I can enjoy an album from start to finish with no gaps between tracks. It’s a beautiful thing!

Can Digital Make a Room Correct?

TL;DR – modern FIR based digital room correction has a place in audiophile playback systems and within limitations can make just about any system more enjoyable; it is no substitute for proper room and system setup, but give it a try!


Ask audiophiles which part of their playback system has the greatest influence on sound quality, and most will agree it’s the room. It dominates 50 to 70% of what we hear. That’s staggering when you think about it! Although a great deal of care likely went into loudspeaker selection, we leave so much performance on the table when we ignore the room’s tremendous contribution to system performance.

If we could start from scratch, we might build a golden ratio based room that’s 16.2ft x 26.2ft with a 10ft ceiling, MDF walls and ceiling, bass traps in the corners, and an appropriate mix of absorption and diffusion to achieve an ideal mix of direct and reflected sound. Loudspeakers with well-behaved off-axis response would help to ensure that reflections do not emphasize any particular band of frequencies.

Back to reality…few of us will have an opportunity to build such a room, so we’re left to play the hand we’re dealt. Often this means our hi-fi shares a room with other activities and associated furniture that limit listening position, loudspeaker placement, and room tuning options. At best, we may have a dedicated room but one that is of less than ideal size, proportions, and materials. In either scenario, anything that we can do to improve the performance of our room will still affect 50-70% of our system’s sound, so even if options are limited, they are worth exploring and re-exploring as technology changes.

Since so much of the sound that reaches the listening position is from room reflections, we want those reflections to be uniform, dictating a symmetrical placement of both listening position and loudspeakers. For example, if we took an overhead map of our room, drew a line from the listening position to a point mid-way between the speakers and folded the map in half along that line, all walls should be perfectly aligned. This is not always possible since many rooms are L-shaped or otherwise not symmetrical, but the acoustic effects of asymmetry can sometimes be reduced somewhat via creative positioning of absorbing and diffusing furniture such as couches and bookshelves and keeping the greatest misalignment behind the listening position. Purpose-built room treatment devices such as corner bass traps, stand or wall mounted absorption panels, and diffusers should be considered if décor permits. Investments of even a few hundred dollars in treatments can bring about dramatic performance improvements.

However, even after we’ve set up and treated the room to the greatest practical extent, frequency response at the listening position likely shows amplitude swings in excess of 20dB. All of that care put into selecting audio components with an accurate response to fractions of a dB across the entire audible range and loudspeakers with on-axis response accurate to +/- a few dB would seem to be wasted given the vast inaccuracies of room response. Fortunately, our brains are remarkably adept at processing what we hear, enabling us to quickly adapt to the uneven response caused by our listening environment. When you go to a friend’s house for a listening session, you may have found that it takes a track or two for you to fully wrap your head around what you are hearing, but after that, the music becomes much more enjoyable. That’s your internal DSP kicking in to make sense of what you’re hearing in the new environment.

But surely those huge errors in amplitude response are masking important details in the music! I imagine that our brains would be more relaxed if we could feed them from a loudspeaker + room system with a more accurate response. Fortunately, in recent years digital room correction systems have become both affordable (in Audiophile terms) and effective at substantially improving system response at the listening position without the awkward phase shifts, noise, and other issues associated with old-school EQ. The better DRC systems address both amplitude and phase response, which can be helpful when using loudspeakers with multiple drivers and complex crossovers. A system setup correctly within a treated room and calibrated using digital room correction may sound different from what you (and your brain) are used to, but it will be more enjoyable to listen to over longer periods of time and sounds great with a broader range of music even at lower playback levels.

Sounds great, right? But DRC has significant limitations that you should be aware of before diving in. Room tuning is about achieving a pleasing balance between direct sound from the loudspeakers and reflected sound from the room. If your listening room is excessively live (hardwood or tile floors, exposed windows, etc.), DRC can’t remove those harsh reflections; attempting DRC without treating strong reflections first will usually make things worse! The DRC system will even out the response at the listening position, but if there are peaks in the reflected energy, DRC may reduce output at those frequencies to compensate, creating dips in the direct sound response. If your loudspeakers don’t have smooth off-axis response, DRC may ruin direct response for the same reason. DRC corrections to low-frequency response are primarily effective only for one listening position. Finally, DRC can’t fix bass nulls due to room modes since these are the result of the destructive interference of long waves affecting specific locations in the room. Increasing output at those frequencies increases the interference also resulting in the same cancellation while overworking your amps and loudspeakers. Bass traps and adjusting the locations of your listening position and loudspeakers are the only way to minimize these nulls. You can, however, use DRC measurement tools to find out if the changes you are making are improving nulls or making them worse.

Naively, one might imagine the ideal amplitude response at the listening position is “flat” since this is what we expect from amplifiers and sources in the playback system. Anyone who has used a real-time analyzer and graphic or parametric EQ can tell you from experience that flat response at the listening position sounds thin, tinny, and generally awful. Since flat doesn’t work, there are a number of proposals for ideal target curves that have more energy at low frequencies and gradually taper off the highs. Popular curves include the B&K curve, the Harman Synthesis curve, and Bob Katz’ flat to 1kHz, then -6bB at 20kHz. However, another DRC gotcha is the notion that there is a single target response curve that is applicable to all rooms. These curves provide a nice starting point, but additional voicing is almost always required to make the system sound natural and really sing. Dr. Floyd E. Toole does a great job of explaining reasons for this in his paper, The Measurement and Calibration of Sound Reproducing Systems.

The approach I take to room tuning with DRC currently looks something like this:

  1. Verify room setup (loudspeakers are level, symmetrically placed relative to room boundaries, toed-in properly, etc.)
  2. Verify locations of absorption/diffusion for first and second reflection points
  3. Tweak listening position to minimize bass nulls
  4. Measure response at the listening position using a professionally calibrated mic
  5. Start with a target correction curve that is -1dB/octave starting at 320Hz (-6dB at 20,480Hz)
  6. Listen to a number of familiar tracks
  7. If the sound is too thin, lower the starting point of the -1dB/octave slope by one octave
  8. If the sound is too bass heavy/think, raise the starting point by one octave
  9. If the bass is too strong at one starting point but too weak when starting one octave higher, select a starting frequency between the two. Attenuation at 20,480Hz is calculated using this formula:


Depending on how things sound from there, I may perform more subtle parametric lifts/dips of fractions of a dB to suit my personal tastes or those of the person who’s room I’m helping to tune. Center frequencies that I tend to focus on include 256Hz, 2,560Hz, and 12,500Hz. I also typically add moderate Q (between 0.95 and 0.99) roll-offs below the cutoff frequency of the loudspeakers and above 20kHz. This process has worked really well in all of the rooms I have tuned so far; however, I am always looking for ways to refine both the process and results and hope to update this page with new findings. The target curve for my main listening room currently looks something like this:

Loft Target Curve

Although systems for correcting room response have been around for many years, audiophiles tend to avoid them because they often create more problems than they solve. Common problems include improving amplitude response at the expense of phase response and correcting room response while ruining direct response. However, I would argue that the technology, while still not particularly user-friendly, is finally mature enough to overcome most audiophile objections. Modern Finite Impulse Response (FIR) based systems can actually improve phase response, and even Infinite Impulse Response (IIR) based systems can improve both frequency response and imaging, assuming room setup issues are addressed first.

The greatest obstacle remaining is working out a comfortable way to integrate DRC technology into our playback systems. Digital room correction, by definition, occurs in the digital domain (specifically PCM)–output of analog sources like turntables, SACD players, and open reel decks must be sampled and converted to digital before applying DRC and then converted back to analog using a DAC. Some audiophiles will take exception to this potentially lossy process; however, I encourage you to keep an open mind and try it anyway. Modern ADC/DAC technology is vastly superior to what was in use back in the twentieth century, and any losses are generally far less significant than distortions introduced by an uncorrected room! Examples of single-box hardware DRC solutions include:

Computer audiophiles have more integration options available to them since their music sources are already in digital form. Popular playback software, including JRiver, HQPlayer, etc. can actually apply FIR based room correction filters on-the-fly during playback. Fans of lossless streaming services like TIDAL will want to look into adding a network audio adapter (NAA) to their playback system. This NAA architecture employs a powerful PC, typically placed in another room, to apply room correction, upsampling, format conversion, etc. on the audio stream. The stream is then transmitted over a local network to the tiny, quiet, solid-state NAA device that is in the playback system and attached to a DAC. The more powerful PC also runs media management and playback software which is operated via a tablet/smartphone-based remote control app. Another option is to simply create a copy the music files with room correction baked into them using an offline process. While applying correction offline will take time (requires about a week for my library), offline convolution can be slightly higher quality, CPU demands on playback hardware are dramatically reduced, and playback latency introduced by real-time convolution is eliminated.

The only way to find out if DRC can significantly improve the sound of your playback system is to give it a try. Here’s a basic parts list that’s relatively inexpensive yet adequate for evaluating the solution in your own room:

Ignoring the cost of the Windows PC, the total cost of the kit is about $226, which is relatively inexpensive in audiophile terms, and the equipment can be used for measuring and tuning your room even if you don’t ultimately decide to keep DRC in your system. Here are several walkthroughs describing how to use this equipment along with software from AudioVero called Acourate:

Although Acourate is not free, Uli does provide a free application for performing the initial pulse measurements required to analyze the room called AcourateLSR2 Logsweep Recorder, which you can download from:

If you assemble the equipment listed above and follow the instructions to record the pulses, Uli has offered to build room correction filters and apply them to a couple of your music files so that you can evaluate the solution in your own room. My Acourate license does not permit me to share the actual filters that the software creates, but I’m happy to apply the filters to a few of your tracks as well to help you evaluate the solution in your own system. Feel free to contact me if I can answer questions or help you get started.

Update: I saw an interesting discussion of target curves for rooms and headphones on Inner Fidelity. Certainly worth taking the time to read. Here’s a link:

Purifying USB

Audiophiles love system tweaks. They are an essential part of the hobby. Get a playback system sounding just the way you like and pretty soon there’s nothing left to do but listen to music. Granted, that’s what the system is for, so there’s nothing wrong with that! But you know what’s even more fun than listening to music on a system that you like and know very well? Rediscovering your music collection after a subtle improvement to said system. Welcome to the audiophile’s hobby!

Now there are a number of ways to approach tweaking that vary widely in cost. Often the best tweaks are free; for example, fine tuning loudspeaker location by shifting them a few more inches away from a wall or adjusting toe-in to maximize soundstage size while maintaining a sharply focused center-fill. Almost endless fun, but eventually you’ll get things dialed in pretty well. From there, you could consider upgrading components, but that’s an expensive way to get your system tweak fix. Fortunately, the industry has responded to the tweaker’s itch with a nearly endless variety of products that promise to enhance our listening experience at a fraction of the cost of a typical high-end component. These range from standard fare like power filtering electrical outlets, isolation platforms, and shielded cables to the rather bizarre, like magic stones, discs, resonators, harmonizers, transducers, and pendulums that claim to do stuff  like channel subtle energy within the human brain aura. I have no idea, but I try not to knock something until I’ve tried it even if I don’t understand how it works or even could work.

Careful though. There is something called placebo effect; applied to this hobby, it’s essentially convincing ourselves that a system sounds different when the actual output has not changed. Listening intently to detect the impact of a change can have a very real effect on how we perceive and process what we’re hearing. Did that new power cable actually improve macro-dynamics, or are we just paying more attention to the percussion solo? Who knows, and to some extent, who cares? If that garden hose sized kevlar wrapped power cable inspires us to pay more attention to our music and enjoy it more as a result, it may be worth the cost–even if the effect is not lasting.

Of course, when it comes to spending my own money or especially making recommendations for friends, I want to be fairly certain that a commercially available tweak is worth its salt and will make a genuine, lasting change for the better. The old audiophile adage, trust your ears sounds nice, but our perceptions are easily fooled. Some claim that rigorous double-blind ABX tests are the surest route, but I don’t personally put much stock in them either; aural memories are just not that reliable. So, like a number of other audiophiles and reviewers, my approach is simple but time consuming: introduce a change and live with it for a number of weeks or months–ideally spending some time listening everyday and at different times of the day since mood can affect how I listen. Once I’m fairly comfortable with the sound, I revert the change. After a few more days, if I find that I don’t miss it, the product is probably not worth buying.

This brings me to my latest tweak evaluation, iFi Audio’s latest USB signal purifying device: the iPurifier2 that Avatar Acoustics sent me to try out. Before getting into what this thing does, I should explain who it is for; USB audio is a Computer Audiophile thing. (in the tone of Jeff Foxworthy)…You might be a computer audiophile if you have ever argued online that playing FLAC is superior to spinning shiny discs. Or, if you have a PC, Mac, tablet, media player, or network audio adapter connected to an external USB DAC in your main playback system, you probably are one. If you have self-identified as a computer audiophile, feel free to skip to the next paragraph. Computer audiophiles use a computer or computer-like device as a digital transport (similar to the CD transports from a decade or two ago). The transport streams digital music, either bit-perfect or intentionally manipulated, to an attached USB DAC, similar to the external S/PDIF connected DACs from years ago. If you are more familiar with vinyl, the PC acts sort-of like the turntable while the USB DAC is kind-of like the phono stage. A bit of a stretch, but hopefully you get the idea.

Why use USB to transfer digital audio? Well, I suppose because it’s there. Early implementations were a mess because the clock used by the DAC came from the PC and was plagued with jitter. Nowadays, virtually all modern USB DACs use an asynchronous protocol to minimize or eliminate the effect of PC transport borne jitter in the audio stream. So, if async DACs are immune to jitter, why not use a standard Belkin USB cable? Hmmm…I suppose you could do that just like you could use lamp cord for speaker wire. If you don’t hear a difference that justifies the incremental spend and you don’t care about having audiophile jewelry in your system, save your money! Thus, if you’re a computer audiophile who has found that purpose-built speaker cables sound better than lamp cord and you are reasonably confident that some USB cables sound better than others, you may be someone who will appreciate the iPurifier2. Others may exit here.

iFi iPurifiers

Okay. Now that it’s just the two of us, I can start talking about the iPurifier2. Far more details are on the iFi website; however, essentially, in most setups, the iPurifier2 (about the size of a big thumb drive) slips onto the end of the USB cable that you currently have plugged into your DAC. Unlike iFi’s previous generation iPurifier, which as far as I can tell just did passive filtering of the data signal, the iPurifier2 is an active device that re-clocks the signal, electrically balances it, and re-generates it before sending it to the DAC. It also includes some clever technology apparently borrowed from the French military to eliminate the effect of noise on the data signal by generating an inverted noise signal and adding that to the power feed. Sounds reasonable, and the claim is up to a 100x reduction in noise. You can tell that this is an active device because, unlike the original, it runs slightly warm to the touch. Far from hot, it’s more like how warm it would be if you walked around for a while with it in your pocket. My understanding is that it re-clocks the USB data signal–not the digital audio stream that’s encapsulated within the USB data stream. Still, feeding the DAC a nice balanced, clean, and properly clocked USB signal seems like a good idea and should make the job easier for the USB receiver chip in the DAC. Now, de-encapsulating, buffering and re-clocking (to femtosecond accuracy) the actual digital audio signal before passing it along to the DAC would be some trick and would enable this device to dramatically elevate the performance of older USB DACs. Don’t get too excited, since I don’t think the iPurifier2 (or any USB purifying device that I’ve heard of) goes that far.

This does make me wonder about the impact of this device for non-audio USB applications though. For example, can I copy data from my USB v2.0 blu-ray drive faster with one of these attached? Possibly, since cleaning up the signal should eliminate re-transmits–if I’m having any to begin with. Since the iPurifier2 re-generates the signal, I wonder what might happen if I took a dozen 5m USB Type-B cables and plugged them all together with iPurifier2’s between them. I assume there would not be enough bus power to run them all, but ignoring that, would it work? Would the resulting signal be as clean or cleaner than what’s at the end of just one of these cables? I wish I had a USB analyzer, oscilloscope, and the necessary gear to try stuff like this.

Back to audio, one thing you may be wondering is if the iFi iPurifier, iPurifier2, and similar products are addressing any real audio problems? I mean, bits are bits, right? I don’t have to worry about USB errors when I save my tax return to a backup drive; that either works or it doesn’t, so why should I have to worry about streaming audio to my DAC? Good question, and I wish I could give you an authoritative answer. I’m just not an expert in this area, so if you are, feel free to comment! What I have discovered is that with fine audio playback, just about everything matters. Mechanical vibrations, radio frequency and electromagnetic interference (RFI and EFI), acoustics, caffeine consumption, if I’m wearing glasses, window treatments, lighting, and even my mood. So, it’s certainly reasonable to expect a device that does all that iFi claims the iPurifier2 does to make an audible improvement in most systems.

The folks at iFi announced the original iPurifier back in December, 2013, and if I recall correctly, it was one of the first products of its kind. Since then, Schiit Audio, Audioquest, UpTone Audio, and Wyred 4 Sound, and iFi again have introduced USB purifying devices, joining rather more obscure products from Empirical Audio and Ultra Fi. But while most vendors are content to have just one product in their line to address USB maladies, iFi at present offers no fewer than five devices plus their own split USB cable to separate USB power and data signals. Among the first to market and having by far the greatest breadth and depth in products makes iFi the undisputed market leader in USB purification for consumer audio applications. The fact that there are now at least a dozen products designed to clean up USB signals in one way or another also suggests that the USB purifier is coming of age and should be considered a standard component in any system with a computer audio source.

I listened to the iPurifier2 everyday for about a month with three different DACs:

  • iFi nano iDSD (stock USB cable)
  • iFi micro iDSD (with iUSBPower, Gemini, and Mercury cables)
  • Schiit Audio Yggdrasil (with iUSBPower, Gemini, and Mercury cables)

Loudspeakers were the very revealing Legacy Audio FOCUS SE, and headphones were Audio Technica ATH-M50x and Sennheiser HD650. PC transports were Quantum Byte Fanless PC powered by a 12V iFi iPower adapter and running Windows 10, JRiver v21, and Fidelizer Pro and a Macbook Pro running JRiver and roon.

When using the iPurifer2 with the iUSBPower, I followed iFi’s recommendation, connecting the iPurifer2 to the input of the iUSBPower rather than the input of the DAC. For comparison, I also had my old first generation iPurifier and UpTone Audio’s USB REGEN which was powered by a bench 5v linear regulated power supply.

The effect that the iPurifer2 had on these different systems was consistent. In all cases, backgrounds were darker and stereo imaging was more focused than setups without it. Vocals on the USB REGEN seemed to have slightly more weight in the lower mids, but soundstage lost focus compared to the iPurifeir2. After listening to these systems for several weeks with the iPurifier2 and then removing it for a while, there was no question that I missed what it did for each of them, making the iPurifier2 a bonafide tweak that adds real value–at least in my systems. Needless to say, I requested an invoice instead of a packing slip for the review sample!

With my wife assisting, I was able to run an unscientific half-blind comparison between the iPurifier and iPurifier2; and with almost perfect accuracy, she was able to detect which one was in the system. While the difference is subtle, it’s not difficult to tell these devices apart once you know what to listen for. The nano iDSD DAC with Macbook Pro combo seems to benefit most from the iPurifier2; however, even the top-flight Yggdrasil’s performance was noticeably improved, with even greater transient attack and focus.

I tried stacking devices but generally did not like the results. For example, the USB REGEN going into the iPurifier2 and then into the iUSBPower sounded a little muddy compared to using either device separately. I suspect the effect is highly system dependent since I have read accounts from others who found combining these devices to be beneficial.

This experience has made me curious about iFi’s new iUSB3.0 products which seem to combine USB data signal purification from the iPurifier2 with USB power replacement from the older iUSBPower. Making the most of an iUSB3.0 requires a split USB cable, like iFI’s Gemini (~$200 USD), which brings up the cost of entry from a little over $100 USD for the iPurifer2 to nearly $400 for the nano iUSB3.0 + Gemini combo or $600 for the micro version. Still these are small figures in audiophile terms. My recommendation? Start with the iPurifier2. If you like what it does, upgrade to one of the iUSB3.0 devices later and shift the iPurifier2 to your mobile rig. Taking this path will maximize the value of your system tweak dollars by giving you two fresh new opportunities to discover greater nuance and detail in your music collection.

Cheers and happy listening!

How we listen

Most of us were brought up with music as a sort-of “soundtrack for our lives”–something that was on while we did other things. We might give it our full attention for a few moments or sing along during our favorite parts, but the concept of sitting completely still and giving attention to nothing other than what’s entering our ears for an extended period of time is a foreign concept to most of us.

Many years ago, before smart phones, the Internet, and cable TV, music playback was less ubiquitous and therefore more appreciated–even a luxury. Playback of recorded music was a special occasion; families and groups of friends would assemble around the record player and listen to entire album sides together without interruption. Odd as this seems in today’s multitasking culture, there are still some who regularly set aside time exclusively for listening to music.

There are many ways to enjoy music playback just like there are many different ways to appreciate most things in life. However, appreciation is almost always enhanced with greater attention. You may have discovered this with other interests like enjoying craft beer, fine wine, single malt scotch, gardening, photography, golf, video games, or just spending time with someone you love. Music is so ubiquitous that it’s easy to forget that this principle applies to enjoying music playback as well.

Deeply appreciating music playback does not require particularly great hearing. Just time and focused attention–being present for the event while limiting distractions. If it’s been a while since you’ve tried this, I encourage you to move your favorite chair to a spot that’s equidistant to your best pair of loudspeakers forming something close to an equilateral triangle. Adjust speakers and/or chair height so that your ears and the tweeters are the same distance from the floor, and toe-in the speakers until most vocals seem to come convincingly from a spot midway between the two speakers. Queue up an album you have not heard in a while and try to listen intently to it from start to finish with no interruptions. Chances are high that you’ll hear things in familiar music that you’ve never noticed before. You may even discover a new perspective on how we listen.