Subject: Re: Frequency response was Re: [linux-audio-user] Audiophile CD's
From: Ben Saylor (bsaylor_AT_macalester.edu)
Date: Mon Jan 28 2002 - 18:07:32 EET
On Mon, Jan 28, 2002 at 03:16:04AM -0500, Jason wrote:
> On Mon, 28 Jan 2002, Paul Winkler wrote:
>
> > On Mon, Jan 28, 2002 at 12:59:10AM -0500, Jason wrote:
> > > and C. Timbre however, is a function of waveshape not frequency; the
> >
> > But any periodic wave's shape can be *completely* described as the sum
> > of sines of various frequencies and phases. Therefore timbre *is* a
> > function of frequency.
>
> True, but I'm not convinced that that necessarily means that everything we
> hear is heard that way because our brains are constantly summing a bunch
> of sine waves.
IIRC, sound is broken into its component sine waves by the cochlea
(inner ear), a coil filled with fluid and lined with nerve endings.
Each nerve ending in the cochlea is stimulated by a particular
frequency. So the information the brain receives is analogous to a
set of frequency coefficients - a bunch of sine waves.
>
> >
> > > Therefore, higher sampling rates are desirable because they do improve the
> > > accuracy of the repesentation of the shape of a waveform.
> >
> > ... by extending the frequency response.
> >
> > If you can hear the difference between a 22 kHz sine wave and a 22 kHz
> > square wave, then you are hearing frequencies at 44 kHz or above.
> > Either that, or you are hearing distortions in the playback system
> > induced by ultrasonic content, which is quite possible.
>
> And this is why the distinction matters, because I certainly can't hear
> sine waves with a frequency much higher than 19.5 kHz, at least, not as of
> the last time I had my ears checked.
>
> However, I can tell the difference between a 16k sine wave and a 16k
> square wave, and I can honestly say that the 16k square wave sounds like a
> square wave, and not simply "different" from the sine wave- It's a pretty
> easy test to execute, I suggest everyone
> interested sampling frequencies conduct it at several different sampling
> rates, it was a bit of a revelation for me- Which means
> that either a.) you can hear much higher frequencies than 20kHz, and your
> brain simply ignores them when they aren't associated with a lower
> fundamental frequency (frankly, that seems a bit unlikely) or b.) The
> brain doesn't process timbre by performing lightning quick FFT on the
> input
> from the audio nerves.
Basically, the audio nerves send to the brain the *results* of an "FFT".
My guess is that the difference you hear is in aliasing or other
distortion caused by whatever systems (re)produced the waves. But I'm
no expert..
>
> I guess it doesn't really matter, because both analyses lead you to the
> same conclusion that 44.1 isn't really adequate. By the same token, it
> makes it incredibly important that the higher frequencies are correctly
> represented. In the last issue of Tape-Op there's an interview with Neve
> that's pertinent to this discussion, he relates an anecdote about Geoff
> Emerick noticing a slight brightness in three channels of the console at
> AIR montserrat and
> upon taking the thing apart, the discoved that the thing was 3dB down at
> something ridiculous like 51k. For most people, I doubt it's something
> they'd notice, and I doubt that Geoff Emerick can hear a 51k sine wave,
> but still, it makes you think.
>
> >
>
> --
> YankTheChain.com - You can pretend we're not here. That's what I do.
>
> ,
>
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