linuxaudio.org

On Wed, Apr 21, 2010 at 4:34 PM, Rob  wrote:

quoted text
> On Wednesday 21 April 2010 02:47 pm, micromoog wrote:

>> > It is easy to understand that this correlation between phase and

>> > correct amplitude also affects frequencies below half the

>> > sampling-rate. Might be as

>> > low as quarter of the sampling-rate, which in case of the CD is 11kHz.

>> This is a pretty bold claim, and contradicts Nyquist and other

>>  literature. Do you have a citation for the claim that frequencies "as

>>  low as a quarter of the sampling-rate" are damaged by sampling?

>

> While I consider this to be an academic discussion since I have high

> frequency hearing loss, it does seem to me that with a sample rate of

> 44.1KHz, a 22.04KHz sine wave is indistinguishable from a 22.04KHz square

> wave despite being below the Nyquist frequency,

In any good system, both are going to be silence, as they've been

entirely lowpassed away.
Choosing something a little lower (like 18kHz), they'll still be

identical, as the harmonics that make a square wave a square wave will

also have been lowpassed away.  The square wave's first harmonic (OK,

it's actually called the 'second harmonic, as the 'first harmonic' is

the fundamental) is at 36kHz, above Nyquist.
When you filter away all the harmonics of a square wave, what do you

get?  A sine wave.

When you filter away all the harmonics of a triangle wave, what do you

get?  A sine wave.
> It seems like a pretty esoteric thing to care about, but if one does care

quoted text
> about frequencies above 11KHz, I guess he really might need to consider

> sample rates higher than 44KHz.

Completely incorrect.  No shred of truth, period.
> The Nyquist frequency is the threshold

quoted text
> above which tones can't be represented at all, not the threshold below

> which tones are represented with any kind of fidelity.

I grant this is an advanced a topic that relatively few people have

studied.  But just because you personally don't understand it doesn't

make it 'not so'.
Monty

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