linuxaudio.org

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

quoted text
> > 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, and an 11025Hz sine wave is

indistinguishable from an 11025Hz triangle wave.  I just fired up Audacity

and generated a tone to verify this.
It seems like a pretty esoteric thing to care about, but if one does care

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

sample rates higher than 44KHz.  The Nyquist frequency is the threshold

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

which tones are represented with any kind of fidelity.  
Rob

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