{"id":57,"date":"2016-04-10T19:15:04","date_gmt":"2016-04-10T19:15:04","guid":{"rendered":"http:\/\/blog.dsnyder.ws-e.com\/?p=57"},"modified":"2020-03-17T16:25:15","modified_gmt":"2020-03-17T23:25:15","slug":"can-digital-make-a-room-correct","status":"publish","type":"post","link":"https:\/\/blog.dsnyder.ws-e.com\/index.php\/2016\/04\/10\/can-digital-make-a-room-correct\/","title":{"rendered":"Can Digital Make a Room Correct?"},"content":{"rendered":"

TL;DR\u00a0<\/strong>– 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\u00a0for proper room and system setup, but\u00a0give it a try!<\/p>\n

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<\/em> when you think about it!\u00a0Although a great deal of care likely went into loudspeaker selection, we leave so much performance on the table when we\u00a0ignore the room’s tremendous contribution to system performance.<\/p>\n

If we could start from scratch, we might build a\u00a0golden ratio<\/a><\/em> 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.<\/p>\n

Back to reality…few of us will have an\u00a0opportunity\u00a0to build such a room, so we’re left\u00a0to play the hand we’re dealt. Often this means our\u00a0hi-fi shares a room with other activities and associated\u00a0furniture that\u00a0limit 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\u00a0room 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.<\/p>\n

Since so much of the sound that reaches the\u00a0listening position is from room reflections, we want those reflections to be uniform, dictating a\u00a0symmetrical placement of both listening position and loudspeakers. For example, if we took an overhead map of our\u00a0room, drew a line from the listening position to a point mid-way between the speakers\u00a0and folded the map\u00a0in half along that line, all\u00a0walls should be perfectly aligned. This is not always possible since many\u00a0rooms are L-shaped or otherwise not symmetrical, but the acoustic effects of asymmetry can sometimes be reduced somewhat\u00a0via 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\u00a0d\u00e9cor permits. Investments of even a few hundred dollars in treatments can bring about dramatic performance improvements.<\/p>\n

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\u00a0accurate 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\u00a0hear, enabling us to quickly adapt\u00a0to 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\u00a0or 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.<\/p>\n

But\u00a0surely\u00a0those huge errors in amplitude response are masking important details in the music! I imagine\u00a0that our brains would\u00a0be more relaxed if we could\u00a0feed them from a loudspeaker + room system with a more accurate response. Fortunately, in recent years digital room correction<\/em> 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\u00a0when 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\u00a0what you (and your brain) are used to, but it will\u00a0be more enjoyable to listen to over longer periods of time and sounds great with a broader range of music even at lower playback levels.<\/p>\n

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\u00a0direct sound from the loudspeakers and\u00a0reflected sound from the room. If your listening room is excessively\u00a0live (hardwood or tile floors, exposed windows, etc.), DRC can’t remove those harsh\u00a0reflections; attempting DRC without treating strong reflections first will usually\u00a0make things worse! The DRC system will even out the\u00a0response at the listening position, but if there are peaks in the reflected energy, DRC may\u00a0reduce output at those\u00a0frequencies to\u00a0compensate, creating dips in the direct sound response. If your loudspeakers don’t have smooth off-axis response, DRC may\u00a0ruin 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\u00a0also 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.<\/p>\n

Naively, one might imagine the ideal amplitude response at the listening position is “flat” since this is what we\u00a0expect from amplifiers and sources in the playback system. Anyone who has used a real-time analyzer<\/em> 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<\/a>, the Harman Synthesis curve<\/a>, and Bob Katz’ flat to 1kHz,\u00a0then\u00a0-6bB at 20kHz<\/em><\/a>. However, another DRC gotcha<\/em> 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\u00a0great job of explaining reasons for this in his paper,\u00a0The Measurement and Calibration of Sound\u00a0Reproducing Systems.<\/a><\/em><\/p>\n

The approach I take to room tuning with DRC currently looks something like this:<\/p>\n

    \n
  1. Verify room setup (loudspeakers are level, symmetrically placed relative to room boundaries, toed-in properly, etc.)<\/li>\n
  2. Verify locations of absorption\/diffusion for first and second reflection points<\/li>\n
  3. Tweak listening position to minimize bass nulls<\/li>\n
  4. Measure response at the listening position using a professionally calibrated mic<\/a><\/li>\n
  5. Start with a target correction curve that is -1dB\/octave starting at 320Hz (-6dB at 20,480Hz)<\/li>\n
  6. Listen to a number of familiar tracks<\/li>\n
  7. If the sound is too thin, lower the starting point of the -1dB\/octave slope by one octave<\/li>\n
  8. If the sound is too bass heavy\/think, raise the starting point by one octave<\/li>\n
  9. If the\u00a0bass is too strong at one starting point but too weak when starting one octave higher, select a starting frequency\u00a0between the two. Attenuation\u00a0at 20,480Hz is calculated using this formula:<\/li>\n<\/ol>\n

    \"drc-tgt-eq\"<\/p>\n

    Depending on how things sound from there, I may perform more subtle parametric lifts\/dips\u00a0of 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\u00a0Q (between 0.95\u00a0and 0.99)\u00a0roll-offs\u00a0below the cutoff frequency of the loudspeakers and above 20kHz. This process has worked really well in all of the rooms I have tuned\u00a0so 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:<\/p>\n

    \"Loft<\/p>\n

    Although systems for correcting room response have been around for many years, audiophiles tend to avoid them because they often\u00a0create more problems than they solve. Common\u00a0problems include improving\u00a0amplitude 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\u00a0Response<\/a><\/em> (FIR) based systems can actually improve phase response, and even Infinite Impulse Response<\/em> (IIR) based systems can improve both frequency response and imaging, assuming room setup issues are addressed first.<\/p>\n

    The greatest obstacle remaining is working out a comfortable way to integrate DRC\u00a0technology into our playback systems. Digital room correction, by definition, occurs in the digital<\/em> domain (specifically PCM)–output of analog sources like turntables, SACD players, and open reel decks must be sampled and converted to digital before applying\u00a0DRC and then converted back to analog using a DAC. Some audiophiles will take exception to this potentially lossy process; however, I encourage you\u00a0to keep an open mind and try it anyway. Modern ADC\/DAC technology is vastly superior to\u00a0what 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:<\/p>\n