Passing args to "do" in SynthDef

Questions
1

I’m trying to control the number of times a “do” loop is run in a SynthDef. I set an arg “passes” to do the looping.
If I hard code a “4.do” I get the result I expect.

( SynthDef( \test, {|out=0,passes=4|
	var sig=0,i;
	4.do { |i| 
		sig = sig + SinOsc.ar(200*i,0,0.05);
	};
	Out.ar(out,sig) 
}).play
)

image
image1114×634 28.9 KB

When I use “passes.do” I only get one sine wave out.

( SynthDef( \test, {|out=0,passes=4|
	var sig=0,i;
	passes.do { |i| 
		sig = sig + SinOsc.ar(200*i,0,0.05);
	};
	Out.ar(out,sig) 
}).play
)

image
image1052×598 2.34 KB

Why is that?

2

This is a very frequently asked question! It’s quite a subtle aspect of Sc. I’m not sure the best place to point you, certainly someone else will know better, but perhaps this as a starting point?

https://doc.sccode.org/Classes/SynthDef.html#Static%20versus%20Dynamic%20Elements

3

I think I get it. I’m guessing when a Synthdef is sent to the server, a static collection of commands is constructed. If I put in a “10.do”, 10 copies of the enclosed function are instanced on the server. This can’t change.

4

Yes, the server reads the file format described at http://doc.sccode.org/Reference/Synth-Definition-File-Format.html

The ugenGraphFunc argument to Synthdef>build has various special rules associated with it.

One is that the function arguments are a kind of metaphor for control parameters, they’re one way to make named controls appear in the graph.

5

Correct. Luckily in many cases it’s still possible to get what you want by replacing one synth with another while it’s running. Take a look at the help for the Ndef class.

6

Thanks,
I’ve seen Ndef as a topic in this forum. I haven’t looked at it yet. It’s akin to Pdef? I’ve used it to replace running patterns.

7

Whoa! Just looked at the Ndef doc and ran the examples. It’s going to take a while to get my head around this.