[A6] Rich, rich, rich

[UnderTow]

On Tue, 25 May 2004 MelloT at aol.com wrote:

> In a message dated 5/18/2004 2:42:51 PM Pacific Standard Time,
> undertow at trance.org writes:
> > With a good 192Khz system (or a DSD system or a even a 96Khz system) you
> > can record a sine wave at 20Khz and reproduce it _exactly_. Even a FFT
> > analyse won't show any differences.

> Note that you can easily hear the difference between a square wave and a sine
> wave at 10kHz. Nothing too special, it seems. Yet, the compoent that makes
> them different is harmonics - the first of which is a 30kHz tone above the 10k
> base fundamental.

It isn't that simple. According to what you say, recording a square wave
at 44.1 or 48 Khz would give us a pure sine at playback. That obviously
isn't the case. What happens is that the harmonics inter-modulate the
base waveform (which is still at it's original frequency). This is akin to
FM and AM.

What you _do_ get is digital quantisation errors (distortion) depending on
the frequency of the intermodulation and the quality of the converters.
The thing is that you always get quantisation errors to a certain degree.
Hence the oversampling DACs at the output. With an 8 times oversampling
DAC you have an anti-aliasing filter starting at arround 176 Khz or so
going down to about 20Khz.

The question is, can we perceive this?  Especially with higher sampling
rates like 88.2Khz , 96Khz etc ...

> So the body can (somehow) perceive things above 20k, just as
> we can also perceive things below 20Hz without "hearing" it.

It has nothing to do with the body perceiving stuff as explained above.
The reason why we perceive loud frequencies below 20Hz has nothing to do
with hearing. Its just the kinetic energy of the accoustic waves shaking
our bodies.

If you percieve loud frequencies above 20Khz you have to start getting
worried because they have to be very loud and they will probably be
causing damage. There are some alarm systems for instance that produce
very loud frequencies at incredibly high sound pressures that will make
the capilaries in your skin burst resulting in bleeding through the pores.
Not nice. But I am drifting from the subject ...

UnderTow