[chuck-users] phase modulation and hard sync?

Alexandre Torres Porres porres at gmail.com
Sun Jun 4 01:35:18 EDT 2017

2017-06-04 0:47 GMT-03:00 Jean Menezes da Rocha <jean at menezesdarocha.info>:

> I managed to install SuperCollider and run your example of Phase
> Modulation. I could achieve the exact same sound with the following ChucK
> code:
> SinOsc mod => SinOsc car => dac;
> 400 => car.freq;
> 201 => mod.freq;
> mod.freq() * Math.PI => float ind => mod.gain; // this bugger works with
> much greater values as standard gain...
> 2 => car.sync; // FM instead of syncing to phase. don't know why...
> while ( true ) {
>     1::second => now;
> }

It might sound the same, or similar, but this is still frequency modulation
and not phase modulation.

> The weird thing is that I had to use 2 (FM) as a value for .sync, contrary
> to my intuition of syncing to phase.

Again, not weird, just a fact that Frequency and Phase modulation are

> Another oddity is the way to calculate the modulation index, which I admit
> was a wild guess that turned out to be correct. I am also curious if anyone
> can explain this.

It's not easy to explain, but you found the magic number/formula that makes
Frequency modulation sound like Phase Modulation.

> However, I am now the one struggling to figure out the difference between
> this phase modulation and FM

In short, they behave differently with the same parameters, but the
parameters can be "converted"/"adjusted" to sound the same.

> syncing to phase, as was my first intuition, yields a rather different
> sound (much harsher) and does not respond to changes to the carrier's
> frequency.

Yep, as I noted, and it is not actually doing phase modulation

Hence, a working phase modulation code still remains mysterious to me.

It seems that when you have a phase input to SinOsc, it'll only consider
that input and disregard any frequency input, is that possible?

Perhaps you can just feed a phase input to SinOsc and then modulate that
signal. Like, send it a phasor input and modulate it. That's gotta work.

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