Sample based synth sustain region produces clicks

SDK Bug Reports
1

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.

Screenshot 2023-10-23 at 14.07.57
Screenshot 2023-10-23 at 14.07.571762×398 93.3 KB

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

2 Likes
3

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

4

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.

5

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)

6

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!)

7

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. :confused: 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.

Screen Shot 2023-10-24 at 4.38.49 PM

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.

1 Like
8

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!

9 
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.

2 Likes
11

Hey @Orllewin, was this working for you before you started this thread? Since updating to 2.1.1 I noticed many of my sample-based synths are now playing distorted sounds or clicking and popping all over the place, I'm trying to figure out if this is related.

And @dave, you mentioned you had a fix, and given 2.1.0 came out a day after this thread, is it safe to say the next OS release should have that fix?

12

Not checked lately - if you have distorted sound, including the system sounds when you hit the menu button, you'll need to restart the Playdate - something's leaking somewhere in the audio engine.

13

Nah, I wish it was that simple, this also happens in the simulator and only for certain sample-based synths that I create and manage, which were working before and haven't changed since. I'll continue to investigate and open a separate bug if needed.