Realtime Control of Synth Parameters for Playing MIDI Sequences

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1

Hi! I'm experimenting with playing a MIDI file. I'm sorry if it's a dumb question, but I am quite confused. Is there any way to adjust the synth parameters for sequence playing at runtime?

I mean, everything is playing fine if I set the synth parameters once during the setup and apply them to the MIDI track instruments. But is there a way to control sustain, attack, and release levels at runtime using a crank or any other input? Repeating all the setup methods for instruments in the update loop doesn't work and seems like an extremely inefficient way to achieve it anyway.

2

It works if I reassign all track instruments once a button is pressed or whatever, but it looks like it stops the playing sequence for one tick while reassigning, so the first time I forgot to call play() again.

So, it's okay as a one-time trigger, but I'm wondering if it is possible to do it gradually. If I place this method to be called in the update, it would surely sound interrupted.

Maybe there is a way to pass not a synth.copy() in addVoice() every time but instead have some "static" synth? Is that even possible? If so, what should I use for it, maybe control signals or an envelope?

function GetInstrument(n)
	local inst = snd.instrument.new()
	for i=1,n do
		inst:addVoice(synth:copy())
	end
	return inst
end

function TestChangeInstruments()

    local crankPosition = playdate.getCrankPosition()
    local sustain = 0
    if crankPosition <= 180 then
        sustain = map(crankPosition, 0, 180, 0, 0.2)
    else
        sustain= map(crankPosition, 180.01, 359.9, 0.8, 1)
    end
        synth:setVolume(0.2)
        synth:setAttack(0)
        synth:setDecay(0.15)
        synth:setSustain(sustain)
        synth:setRelease(0)

    for i=1,ntracks do
        local track = s:getTrackAtIndex(i)
        if track ~= nil then
            local n = track:getPolyphony(i)
            track:setInstrument(GetInstument(n))
        end
    end
    s:play()
end
3

Ok, looks like I got it to work! I made an array of synths and assigned each to instruments instead of copying the same one. Now I just change the values of these synths in a loop instead of reassigning all instruments, so there is no need to call sequence:play() each time.

But maybe there is a much smarter way to achieve the same thing, I don't know.

function GetSynth()
    local synth = snd.synth.new(snd.kWaveTriangle)
    synth:setVolume(0.2)
    synth:setAttack(0)
    synth:setDecay(0.15)
    synth:setSustain(0.2)
    synth:setRelease(0)
    return synth
end

local synths = {}
for i = 1, 18 do 
    synths[i] = GetSynth()
end

local synthCounter = 1

function GetInstrument(n)
	local inst = snd.instrument.new()
	for i=1,n do
		inst:addVoice(synths[synthCounter])
        synthCounter = synthCounter+1
	end
	return inst
end

local ntracks = s:getTrackCount()

for i=1,ntracks do
	local track = s:getTrackAtIndex(i)
	if track ~= nil then
		local n = track:getPolyphony(i)
		track:setInstrument(GetInstrument(n))
	end
end


function ChangeInstruments()

    local crankPosition = playdate.getCrankPosition()
    local sustain = 0
    if crankPosition <= 180 then
        sustain = map(crankPosition, 0, 180, 0, 0.2)
    else
        sustain= map(crankPosition, 180.01, 359.9, 0.8, 1)
    end

    for i = 1, #synths do
        synths[i]:setSustain(sustain)
    end
end