Audio Glitching with VCA Velocity

[erroms11]

Been playing the P-10 a whole lot, and first off wanted to say what absolutely incredible sounding synth. Kudos to everyone at Cherry Audio, amazing work!

Wanted to reach out, because I am experiencing audio glitching / popping, and from what I can tell from my testing it's all linked to when the Velocity control is on for the VCA. Just the VCA, Velocity control on the VCF does not cause this issue. And this happening across a variety of different patches.

If the Velocity is set to zero, I'm getting no audio glitching at all from the synth. But when it's turned on to any degree, I am getting audio popping / glitches every few notes at the very start of playing a note. I've experimented with adjusting the oversampling, changing the buffer size on my ASIO, as well as a host of other settings in my DAW (I'm using REAPER) but I can tell it's coming directly from the plugin itself, as the audio glitches are affected by other FX on the track.

Let me know if there's any other info I can provide, curious to know if anyone else has experienced this issue?

Thanks!

[utdgrant]

This might be due to the way velocity affects the overall amplitude of each voice's envelope generator.

If the velocity immediately jumps to a new value, you will hear a discontinuity in the audio output - i.e. a 'click'.

This effect is illustrated in this Voltage Modular patch:

YouTube video of rapid velocity changes.

In contrast, if you make the velocity affect the 'target' values of the VCA's envelope generator, then clicks are eliminated:

YouTube video of smoothed velocity when using the MRB Laboratory Velocity Envelope.

[utdgrant]

Dealing with velocity as applied to VCAs is something which can cause clicking problems in the analogue hardware world, too.

See this discussion on ModWiggler.

Hardware (and software) envelopes which do a hard return to zero whenever a new note is played can also cause nasty clicks, even when velocity isn't used. This effect occurs if the previous note is still executing its Release Phase towards 0V (and silence). A new note resets the envelope generator's output immediately back to 0V and re-enters the Attack Phase, which causes a sharp discontinuity in the audio output.

And yes, RTZ envelopes are something of an unhealthy obsession of mine!

[erroms11]

Thank you for this incredible information @utdgrant!
I think this may be exactly what I have been experiencing.
In doing more and more testing, this is happening on my other Cherry Audio synth, the Elka-X.
The popping at the start of playing a note is most noticeable when the envelope is pretty closed (having it open masks the popping quite a bit, but it's definitely still there)
I noticed several things that make me think you are correct.
The popping happens more frequently with:
1 - Longer release times on the amplifier envelope
2 - LESS voices selected: The lower the voices, the more frequent the popping!

I've also continued to try multiple combinations of buffer sizing and sample rates on my ASIO, plus oversampling on the synth itself. No combination of any of these seem to affect the frequency of the popping at the start of playing on note on my CA synths. So I believe it may be safe to rule out any CPU load issues, which I didn't think was the case, I'm using an AMD Ryzen 9 7600x on a machine dedicated to music production.

Should also note I have tested the CA synths in Reaper, their stand-alone players, and Ableton. All with the same exact results.

So I wonder, can anyone else replicate this issue then? Is anyone else experiencing this on their CA synths?

Again to summarize: Popping at the start of notes whenever there is any amount of velocity sensitivity on the amplifier envelope, exacerbated by lower voice counts and longer release times on the amplifier envelope.

[utdgrant]

The popping happens more frequently with:
1 - Longer release times on the amplifier envelope
2 - LESS voices selected: The lower the voices, the more frequent the popping!

So I wonder, can anyone else replicate this issue then? Is anyone else experiencing this on their CA synths?

Yeah, it happens on Mercury 4 (YouTube link), too. Particularly in mono mode (1 voice selected).

That's not to rag on Cherry Audio synths specifically. All synths which apply velocity to the final output VCA will be affected by this issue, whether they be hardware analogue, hardware digital or software plug-in. As you point out, the effect becomes much more prominent with restricted voice count and [ETA] long release times.

It's impossible to mitigate this phenomenon with one generic solution, so I do have sympathy for all synth designers. It's up to us as users of these tools to understand why the effect happens in each specific situation, and to work around it in an intelligent way.