[Don Pearce[_3_]]

On Sat, 9 Feb 2019 06:46:35 -0500, Mike Rivers
wrote:

On 2/9/2019 4:06 AM, Don Pearce wrote:
nickbatz wrote:

what is the argument for storing audio files post-converter at anything over 44.1/48 if the filtering is being done way above the audible spectrum anyway?

OK, now I get you. Very little point at all, unless you are doing
something other than reproduce sound. The response of even the best
microphones will go horribly peaky above 20kHz, and it is as well to
get rid of it. All that extra spectrum can possibly do is waste power,
and possibly cause intermodulation distortion down into the actual
audible range.

Ages ago, it seems, a sample company came up with 96 kHz and 192 kHz
sample sets for their pipe organs. Nick probably remembers them. I asked
why, and the reply wasn't absurdly silly. They sample individual pipes.
There are mics that can indeed capture sound above 20 kHz fairly
accurately. What they're sampling has overtones higher than 20 kHz. They
don't travel very far, but they can interact with other overtones and
fundamentals. Call it IM distortion (it is) but that's the way the
instrument works.

When they play back the samples, they have to reproduce those ultrasonic
frequencies, and they do (they sold complete electronic organ systems).
At the time, they needed a rack of about 8 computers to build an organ
playback system. I suspect that after selling two or three systems, they
went out of business or changed their business. But it was an
interesting concept from back in the day when samples were something you
used to make beats, before they were called beats.

Well, intermodulation is a distortion problem, but beats are linear -
just superposition. And no tone is actually generated at the beat
frequency.

And of course if the original high tones have already generated
audible tones by way of intermod, then you only need the audible
spectrum recorded to reproduce them. It may be that the interaction
happens later - the ear is the only place that can happen as air is
not non-linear at these levels. But the interaction will depend on
absolute volume levels, and accurate re-creation is very unlikely.

d