[sdiy] samp. freq for ADSR ?

[phillip m gallo]

If you are phase locked to the waveform you are sampling then yes a square
wave will result.

The Nyquist Theorem, which states that the highest frequency which can be
accurately represented is less than one-half of the sampling rate, is often
mis-understood to say "must be exactly 1/2 of the sample rate".  It is the
"less than 1/2" that allows succesive samples to not occur at the same
location of the wave being sampled and thus successive cycles being
represented by a succesion of different "moments" across the full wave form
reconstructs nicely.  The more samples per cycle (higher S.Rate), the more
accurate the representation, of course.

So the Buchla Example would be best re-stated  .."Creating a 500Hz sampling
frequency... leaving the Buchla MARF with a maximum of" 249.99Hz ....

regards,
p

-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Robert Holmström
Sent: Sunday, April 04, 2004 2:59 PM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] samp. freq for ADSR ?


> > > 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).
> >

I am not an expert in this so maybe somebody can explain it (simple) but
this is how I understand it.

As written above the maximum sampled frequency is half the sample rate. This
means that if I want a 1Hz (low, just as an example) signal sampled, the
minimum samplingfrequency should be 2Hz.

That sampled signal would be a 1Hz "square waveform" because only two
samples are taken in one full wave cycle. If I need any precision in the
sampled signal (like if the source was a saw waveform), I need higher
samplerate.

If the above is a correct explanation (?) that would explain why bass sounds
sound "good" on lower sample rates while high frequencys sounds "metallic".
The bass frequency waveforms are so long that a lower sample rate still
gives us an "accurate" sampled wave.

Maybe I went a bit outside the ADSR subject, but I have wanted to ask this
for soo long that I thought it was good.


Robert

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