[sdiy] Envelope attack smoothing for drum question

Florian Anwander fanwander at mnet-online.de
Fri Aug 21 17:49:42 CEST 2020

Hi Mattias, Didier

To be honest: one of the interesting parts of the 808 *is*, that there 
is no oscillator to sync, but that the trigger initializes the resonance 
of a T-filter. This means also: if the circuit is still resonating when 
a trigger comes in it depends heavily on in which "direction" the 
T-filter is swinging at that moment. That is how a real drum head is 
behaving: if the stick hits the drumhead, while it is moving up, then 
the resulting sound will be different from the sound of a drumhead 
moving down, while hit by the drumstick.

If you do the drum synthesis with an oscillator+VCA concept then you 
should think about provide a choice whether to sync the oscillator or not.

And another note about syncing. I remember a drumsynth (don't know which 
one - was it the 909?), which did not reset the oscillator by the 
trigger, but the trigger switched the frequency of the oscillator or 
T-filter to a higher frequency for a very short moment. This has the 
same effect as a sync, but sounds more "natural".


Am 20.08.20 um 00:01 schrieb Mattias Rickardsson:
> Hi there!
> A smoothing of the envelope will likely not be slow enough to avoid 
> your problem for low frequencies, and will affect the sound too much. 
> And the drum hits will still be inconsistent when the oscillator is at 
> random phases.
> Instead, not immediately simple but anyway:
> Implement an oscillator sync mechanism that resets the triangle wave 
> to its center value and starts in a certain direction, so that it 
> always starts in the same way when the envelope is triggered.
> It will likely not be obvious how to do this, but I've done it and I'm 
> sure it will be possible in your design too with quite few components. 
> In a drum synth it will be worth it! Unsynced oscillators are for 
> string synths. ;-)
> /mr
> Den ons 19 aug. 2020 23:41Didier Leplae via Synth-diy 
> <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> skrev:
>     We are working on an analog drum module that uses a simple
>     envelope created from a trigger to control the amplitude of a
>     triangle oscillator with a basic OTA based VCA.
>     We are having a problem with a slight clicking sound at the
>     beginning of many of the drum hits. We think this is because the
>     attack of our envelope is so sharp that the beginning of our drum
>     hit looks like a straight jump from 0V to wherever the triangle
>     wave happens to fall. Therefore the click is somewhat random in
>     that it doesn't occur when the triangle happens to be low at the
>     time of attack.
>     Can anyone suggest a simple way to deal with this, like adding a
>     slight bit of attack time to the envelope? How could this be done
>     without adding too many parts?
>     Thanks,
>     Didier
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