Sample based synth sustain region produces clicks

[Orllewin]

If you create a synth using a sample and set the sustain frames there's an audible click when the sustain region loops:

local path = "Samples/pcm/sandman_pad", 
self.sample = playdate.sound.sample.new(path)
self.sampleSynth = playdate.sound.synth.new(self.sample, 40804, 125326)

Then play a long note.

To test I've exageratted the sustain boundary - fading in from 40804, and out to 125326 - so it should be looping at a silent point back to a silent point.

Looping this selection in Audacity is smooth, and the frame/sample values come from those loop points, but Playdate produces an audible click at most notes - some lower notes sometimes sustain smoothly (and sound great!).

I may be missig something here, but I think this is an issue in the synth implementation.

Cheers,
Orllewin

[Orllewin]

Actually, it turns out any sample based synth produces clicks when playing notes... there's something very broken here.

[dave (Dave Hayden)]

By "any sample based synth" do you mean regardless of looping? Where is the clicking happening?

Regarding the looping, is the file encoded with ADPCM, by chance? For some reason I don't remember now I commented out the code that sets the position inside of the ADPCM block when it loops, so it's always jumps to the beginning of the block instead. I'll take a look at that now, see if I can figure out if that was intentional or not and get it working correctly again.

[Orllewin]

No, I was sure to use PCM for these. You can hear the clicks and pops in this video: https://www.youtube.com/watch?v=KvH9JL0IWqw

It doesn't always happen, but if you retrigger a lot you get lots of pops. This is all manual so it's repeat calls to playMidiNote. The underlying audio implementation is really simple, just your basic Lua API wrapped in a fancy UI!

So the pops are either happening at the start of playing a new note, or when terminating a currently playing note.

The sustain region too, same deal when it loops (I've turned that off for now)

[Orllewin]

I've managed to mitigate this (in a quite expensive manner) by fading out the playing note before triggering the new note:

self.releaseTimer = playdate.timer.new(100, 1.0, 0.0)
self.releaseTimer.updateCallback = function(timer)
	self.sampleSynth:setVolume(timer.value)
end
self.releaseTimer.timerEndedCallback = function(timer)
	self.sampleSynth:setVolume(1)
	self.sampleSynth:playMIDINote(math.floor(event:getValue()), 1)
end	

So the pops and clicks are happening when terminating the currently playing note.

(This is all unrelated to the sustain region issue of course!)

[dave (Dave Hayden)]

I'm not totally clear on how this is put together, but could you use the envelope to fade it out instead?

self.sampleSynth:setRelease(0.1)
self.sampleSynth:setFinishCallback(function(s) s:playMIDINote(math.floor(event:getValue()) end)

About the clicking: I've got a fix for the looping, wasn't chopping the frame up correctly. This looks like another place where I roughed in the code and forgot to go back and finish it. Explains the lack of docs, too. The click when triggering a note while it's already playing is a bit trickier, since it jumps immediately back to the start of the data.

A crossfade would be ideal but a bit of work. The simplest workaround I can think of is to use two synths there and ping-pong between them so you can play the note for the next event while letting the previous finish on its own.

[Orllewin]

Aaah brilliant, thank you for looking into it, glad it wasn't me doing something silly. I did notice some improvement with sustain when I turned off dithering when exporting hits from Ableton but it still had noticeable artefacts.

I'll find the lightest way of working around things when retriggering a note, this timer solution is far too heavy (sounds great though: https://www.youtube.com/watch?v=KKrzh5pRDTo ), having a release with callback would be better if I can get it to work - only one synth per 'synth' then... but two synths better than spawning a timer every note!

[Orllewin]

if self.sampleSynthA:isPlaying() then
	self.sampleSynthA:noteOff()
	self.sampleSynthB:playMIDINote(math.floor(event:getValue()))
elseif self.sampleSynthB:isPlaying() then
	self.sampleSynthB:noteOff()
	self.sampleSynthA:playMIDINote(math.floor(event:getValue()))
else
	self.sampleSynthA:playMIDINote(math.floor(event:getValue()))
end

This works beautifully.