[sdiy] samp. freq for ADSR ?

[Magnus Danielson]

From: ASSI <Stromeko at compuserve.de>
Subject: Re: [sdiy] samp. freq for ADSR ?
Date: Sun, 4 Apr 2004 22:59:42 +0200
Message-ID: <0404042259420A.00646 at Robert>

> On Friday 02 April 2004 22:13, mark verbos wrote:
> > Creating a 500Hz sampling frequency. Nyquist's theory is that the
> > maximum sampled frequency is half the sample rate, leaving the Buchla
> > MARF with a maximum of 250Hz (real low for audio).
> 
> This is a common misinterpretation of the Nyquist Theorem.

Actually no, it is a correct interpretation of the Nyquist Theorem, but it is
not a practical interpretation of the Nyquist Theorem as you want to point out.

> The ideal reconstruction filter that would be necessary to reproduce a signal
> at fs/2 is not realizable (provided that the exact bandlimiting to fs/2 was
> possible in the first place). If the reconstruction filter is not perfect,
> frequencies well above fs/2 and of course aliasing are the result. The
> reconstruction filter is also often used to attenuate quantization noise.
> Even though the latter does not really have to do with the Nyquist theorem,
> all this means that you will often want to use oversampling of at least
> eight.

True, but these are practical engineering concerns. Stuff like oversampling
etc. helps to refine the picture of how it actually works. It is worth
mentioning that the frequency mirroring as allows us to select to filter out
some other mirror part than the base signal variant.

Cheers,
Magnus