[sdiy] Oberheim Xpander Envelopes and LFOs etc

[Tristan Upton]

Hi John, 

The Nord Modular uses 24kHz (1/4 of the 96kHz audio sampling rate) for 
control signals. It seems fairly smooth most of the time, but if you sum or 
modulate audio signals with control signals it can besome noticeable. I 
believe with the Nord G2 you can uprate control signals to run at the full 
96kHz audio rate. 

The Kurzeil K2X00 series use a 50Hz calculation rate for control signals and 
modulation. I think they then linearly (or otherwise) interpolate between 
these values to smooth them out. For most purposes it is fine but if you use 
fast LFOs, up towards to 20Hz, then the modulation waveform audibly turns to 
mush. 

Because of the 50Hz update rate the first step from 0 envelope attack time 
to 20mS on the K2000 is fairly coarse. So on the K2500 and later machines a 
variable shaped attack slope was introduced. This is only implemented on the 
amp envelope but it does give better control over the important attack 
transient. 

Regards, 

Tristan 

John Mahoney writes: 

> At 07:56 AM 9/30/2007, Tom Wiltshire wrote:
>> [snip]
>> So the question is "How low can you go?". 53Hz might be really silly,
>> but would 1KHz be enough? 5KHz? I know some of the software sound
>> languages (csound or puredata) use rates of 6KHz or so. 
>> 
>> What counts as a reasonable sampling rate for LFOs and Envelopes?
> 
> 44.1kHz would support sampled envelopes and waves as well as audio rate 
> modulation. (Might as well do sampling and wavetables, if you are going 
> that far.) Crazy, I know.
> --
> john 
> 
> "Piece of cake with an FPGA," replies Scott Gravenhorst. ;-)
> "Piece of cake with software," adds someone else.  
> 
> 
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