[sdiy] Envelope attack smoothing for drum question

Mattias Rickardsson mr at analogue.org
Fri Aug 21 23:06:32 CEST 2020


On Fri, 21 Aug 2020 at 18:54, Ian Fritz <ijfritz at comcast.net> wrote:

> MR—
>
> Your method is very interesting. Are the details up anywhere?
>

No, I'm sorry I can't spill more details since it's being used
commercially. I'll leave the rest as an exercise for the reader. O:-)


> It sounds vaguely related to the “kick sync” I developed for my Tri VCO.
>  http://ijfritz.byethost4.com/sy_cir4.htm
> This uses short pulses derived from the master osc to nudge the slave’s
> phase until a synch’ed equilibrium is reached.  Maybe a sort of softish
> version of what you do.
>

Funny that you say that, because I thought the other day "hmm, what should
this type of sync be called, I wonder if someone has come up with a name
for it already... Kick sync would be suitable - ah, this must be the same
as Ian's kick sync!" But then I looked it up and it wasn't the same after
all. Yes, perhaps like a softish version. :-)

/mr


On Aug 21, 2020, at 1:05 AM, Mattias Rickardsson <mr at analogue.org> wrote:
>
> 
> Discharging the cap to any phase could be tricky, yes. Maybe not worth it.
>
> Instead of discharging the oscillator cap in ordinary fashion,
> synchronization can be implemented by speeding up the oscillator for a
> short while until it reaches the desired start phase. It kind of
> fast-forwards or fast-reverses the waveform to the starting point.
>
> This can be done by feeding it with a high CV spike generated by a
> comparator-based circuit that uses the oscillator state and the incoming
> sync pulse to start the CV spike, end it at the right moment, and also
> handle the direction control of the oscillator during and after the spike.
> This might seem very elaborate, but the added circuitry is not that
> different from the standard mechanisms already available in a triangle
> oscillator.
>
> Can't give any pointers to schematics since I don't remember ever seeing
> this in any other construction, but it ended up quite minimal needing very
> few extra components and was well worth a couple of days of thrilling
> research. :-)
>
> /mr
>
> Den tors 20 aug. 2020 23:27Didier Leplae <didierleplae at yahoo.com> skrev:
>
>> We are experimenting with using a jfet, in the same way the sync on a VCO
>> would work, but have not gotten it to work yet.
>>
>> How would you be able to control the different start phases?
>>
>>
>> On Aug 20, 2020, at 1:16 PM, Mattias Rickardsson <mr at analogue.org> wrote:
>>
>> 
>> On Thu, 20 Aug 2020 at 18:10, Didier Leplae <didierleplae at yahoo.com>
>> wrote:
>>
>>> Yes! This makes so much more sense than what we were thinking.
>>> Thank you Matthias!
>>>
>>
>> No problem!
>> Btw, when thinking about this it might be worthwhile checking out
>> different start phases for the synced oscillator waveform, if possible.
>> Perhaps starting in the middle isn't punchy enough (cf. the TR-808 bass
>> drum initial click, for instance). :-)
>>
>> /mr
>>
>>
>>
>>
>>>
>>> On Aug 19, 2020, at 5:02 PM, Mattias Rickardsson <mr at analogue.org>
>>> wrote:
>>>
>>> 
>>> 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> 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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