Thursday, April 3, 2014

Do we need audio bandwidth above 20kHz?

Previous post linked to articles related to what has been called "audio objectivism" that all we need is audio equipment with 20Hz - 20kHz bandwidth and other similar easily measurable and long accepted "high fidelity" requirements.  Now, with audio downloads going to 24bit/96kHz and 24bit/192kHz PCM formats and DSD (which also has significantly higher bandwidth than 20kHz, though the upper bandwidth may be more corrupted by noise than PCM formats), a particular question is whether we specifically need audio bandwidth extended beyond 20kHz, and if so, how far?  Here's the article I linked previously which is primarily concerned with this question specifically, and it may be worth reading despite the incredible one-sidedness, condescending tone and over simplistic diagrams.  It is the discussion on digital audio sampling here which is comparatively well presented.


Now I've found a wealth of other information about the bandwidth topic.  And more test material!  Unfortunately, not enough to reach any sort of conclusion, but enough to know this is a serious issue and that many people taking the "higher bandwidth" side are indeed very serious audio engineers and scientists, not the starry eyed kooks and charlatans you would think they were from only reading audio objectivists--who would like you to believe this is an open and shut case and no qualified audio engineer would think otherwise for a second.

Here is one of the best summaries I've found, written by the famous audio reviewer Martin Colloms.  I must say I was very surprised to find him ultimately taking the lower bandwidth side, but his paper is very useful  because he takes the issue seriously and documents many important studies with contradictory results.  I was surprised because of my previous knowledge of reviews written by Colloms, and if you take a look at other articles in his archive, you find that has often not been on the side of the audio objectivists with regards to things like the need for special capacitors (above and beyond what would be required to achieve 20-20kHz bandwidth--for which almost any available capacitors would do fine) and exotic Class A power amplifiers (audio objectivists claim all reasonably well designed audio power amplifiers today, with THD less than 1%, 20-20kHz bandwidth and flat frequency response sound identical, so one might has well have Class AB or D amplifier that meets these specifications than an extremely expensive and high quiescent power consuming equivalent Class A amplifier whose advantages over a well designed Class AB amplifier might not even be measurable in the ways suggested by audio objectivists).

I discovered the Colloms article reading this long and argumentative blog about 192kHz downloads at Steve Hoffman's forums.  This blog is very good reading, once you get past the useless posts, it is full of arguments and evidence on both sides, and having links to articles on both sides.  Unlike many others long blogs I've seen that are often more heat than light.  Just to specifically link some of the things it links, famous audio engineer and scientist (Cal Tech professor) James Boyk has long taken the higher bandwidth side.  In this paper, he merely shows that musical instruments produce significant acoustical energy above 20kHz, and then he simply refers to experiments by others showing this has effects on humans, some of the same studies discussed by Colloms.

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