[sdiy] Digital pots for polyphonic portamento..

[Andrew Simper]

I can definitely vouch for calculating digital RC at control rate and 
doing linear interpolation between those values. If you have a slow 
moving signal this gives very good results with minimal cpu. I've used 
this throughout the D-CAM: Synth Squad product and it is very effective.

Andy


Antti Huovilainen wrote:
> On Thu, 5 Mar 2009, Jean-Pierre Desrochers wrote:
>
>> i need these 2688 steps in a 5 sec portamento to hear
>> a glide without staircase effect..
>> But doing so,  the worst case in my example is min portamento which is
>> 2 msec overall glide time --> 2msec. / 2688 steps = 744nanosec. per 
>> DAC steps!!!!
>>
>> Do you have a solution on that?
>
> Yes. You keep a constant update rate and stick an RC smoothing filter 
> after the dac. The RC filter time constant should be about the same as 
> your update rate. So for 1 kHz update rate the TC would be 1ms.
>
> If you don't have enough cpu to calculate RC glide at 1 kHz rate, you 
> can lower that rate to say 1/10th and use linear interpolation 
> in-between.
>
> Antti
>
> "No boom today. Boom tomorrow. There's always a boom tomorrow"
>   -- Lt. Cmdr. Ivanova
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