[sdiy] Envelope attack smoothing for drum question

rburnett at richieburnett.co.uk rburnett at richieburnett.co.uk
Fri Aug 21 18:37:43 CEST 2020

Florian, The 808 shortens the period of oscillation (raises the pitch) 
in the kick drum T-filter for a brief period immediately following the 
trigger pulse.  As you say this further enhances the attack transient.

The 909 refines this pitch modulation by providing a continuous pitch 
sweep (chirp) throughout the duration of its kick drum sound, rather 
than just switching between a high and low resonant frequency.


On 2020-08-21 16:49, Florian Anwander wrote:
> 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".
> Florian
> 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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