[sdiy] Wavetable lengts during scan!

[ASSI]

On Donnerstag, 3. August 2006 21:56, karl dalen wrote:
> I wonder how long should a wavetable be to avoid
> the *gritting/grinding/stepping sound during adress
> scan trough the table?

If you are talking about scanning the wavetable at arbitrary moments in 
time, the answer is that it depends on the phase velocity and on the 
content of the wavetable.  Obviously if all waves are the same, there 
is no grinding sound from scanning the table.  If OTOH every second 
wave is the exact opposite from it's neighbour then you can make the 
wavetable as long a s you want and you still get audible artefacts from 
scanning it.  The proven method to avoid most artefacts is to switch to 
a new wave only at a zero crossing.  This is a zero decode and an M/S FF 
if the sampling rate is a multiple of your output frequency or (if 
fixed) high enough not to miss a code, otherwise you need a zero 
crossing detector (must work both ways if the oscillator can do FM with 
negative frequencies).  Still, this does not help at all if the reason 
for the stepping sound is a glitchy decode on the wavetable RAM/ROM 
coupled with an asynchroneous DAC.


Achim.
-- 
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