Multi-Channel Crossfade

Questions
1

Hi all -

I’d like to cross-fade between one set of 8 channels and another set of 8 channels.
Since XFader2 seems to be specifically for sets of stereo pairs, I have been trying to find another way around this problem.

I tried to make an abstraction that would take any size input and cross-fade with the alternating channels.
This didn’t quite work as expected, so I thought I’d share it here and see if anyone had any pointers.
Thanks!

VariFade{
	  *ar {
		arg signal, pan, level;
		var out, newSig;

		signal = signal.collect{|x, index|
			index = index+1;
			if (index%2==0,
				{pan = pan;},
				{pan = 0 - pan});
			x = x*pan;
		};
		out = signal;
		^out;
	}
}

And some quick code to run it:

s.meter;
s.options.numOutputBusChannels_(4);
s.reboot;

{
	VariFade.ar(
	[SinOsc.ar(400, mul:0.1), 
		SinOsc.ar(500, mul:0.1), 
		SinOsc.ar(405, mul:0.1), 
		SinOsc.ar(505, mul:0.1)], 
	SawDPW.ar(1).range(-1, 1))}.play;
2

I think the issue is that the abstraction doesn’t know how many channels to consolidate to…but I’m not sure how to fix that.

3

If you’re synthesizing the channels yourself, there’s no need to make them into a flat array. SC supports nested arrays, and XFade2 can multichannel expand:

(
{
	var snd;
	snd = [
		[SinOsc.ar(440), SinOsc.ar(1000), SinOsc.ar(100)],
		[Saw.ar(440), Saw.ar(300), Saw.ar(440)]
	];
	XFade2.ar(snd[0], snd[1], MouseX.kr(-1, 1));
}.play(fadeTime: 0);
)

If you are receiving the channels as an interleaved flat array, you can reshape them into a 2D array using snd.clump(2).flop or snd.unlace(2).

2 Likes
4

possibly also have a look at SelectX:

The output is mixed from an array of inputs, performing an equal power crossfade between two adjacent channels.

1 Like
5

Just one other question about clump, flop, unlace, etc…
Is there a simple command to expand an array as such?
[0, 1, 2] → [0, 0, 0], [1, 1, 1], [2, 2, 2]

6

Like this?

[0, 1, 2].dupEach(3).clump(3)

or

[0, 1, 2].collect { |item| item ! 3 }

You should have asked separately. I think one of the moderators will move the last two posts to a new thread.