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PM with Phaser?
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author PM with Phaser?
maybe a stupid question: but is it possible to do audio rate phase modulation (pm) of any given audio signal with a phaser? (Like the pm of the Malekko Richter oscillator for example?)
Yes, but it probably won't sound the way you expect. I've tried this with Doepfer and Cwejman phasers and the result is too frequency-dependent. If you think of the phaser as multiple all-pass filters, it becomes clear why. Strangely, I did get closer to the depth of modulation I wanted with the Nord Modular phaser, but that has a PM VCO anyway ...

If you want to experiment with the Richter method, get a comparator and follow the block diagram in the manual to Doepfer's A-137-2. This module is essentially the Richter x4, but you need to provide the wave-shaping if you want something other than a saw or square.
Wow, thank you so much for the info about the "comparator" trick. That's exactly what I was looking for!

So, by doing this, you can turn every VCO into an analog phase modulation VCO like the Richter one? (Ok, not for squares as pointed out at the Doepfer site). In fact I'm looking for phase modulation of sine signals (unfortunately something the Richter is not capable of).

By doing this, I could phase modulate a sine signal with a sine modulator which will in fact be identical to thru-zero frequency modulation.... It's motherfucking bacon yo

... or am I'm missing something important here (because you mentioned, it wouldn't sound the way I expect)? hmmm.....
You start with a sawtooth and 'measure' the phase offset against that. Then you would convert the phase shifted saw into a sine. That is the tricky part.

I have built a DIY module that does this. A soon-to-be-released commercial module (not mine) uses another approach to offer much deeper modulation.
Sorry, I didn't really get it. I wanted to start with "real" sines (from a self-resonating filter for example). The only difficult part I could imagine would be to find the right level of the output of the comparator...
Dave Peck
Here's a link to a thread I started over at Gearslutz about the Hordijk dual phaser module. There are lots of audio clips in the thread, including one in post #11 that gives an example of using the phaser for audio-rate phase modulation of a sine wave. -music-production/389492-wonderful-new-phase-shifter-module.html
Looking closer at the pic on the Doepfer site, I recognize that it might only work with saw signals. With sines it will produce "something", but definitely not a phase shifted copy.

At least, I know now why the Richter has no shifted sine output. ;-)

However, your example, Dave, sounds great!
Dave Peck
Thanks, proturboplus. I highly recommend the Hordijk Dual Phaser module. It sounds great and it is far more versatile and capable than a typical phase shifter module.
Yes, this method requires a saw input to generate the phase modulation. I don't think that's why the Richter VCO doesn't have a sine though. It has a triangle, after all.

Dave, that sounds great. With the sine as both carrier and modulator, it might be closer to AM or non-linear distortion though hmmm.....
Yes, but the Richter VCO has a saw core, so I think it will only do the "phase trick" for the saw core and them transform it afterwards into the other waveforms.

Regarding Dave's example, self modulation is no problem when doing phase modulation instead of frequency modulation (as far as I know)... that's one of the beauties of pm. :-)
There's always the WMD PDO. It's made for phase modulation according to the product description.
Yes, but it's digital. That's cheating wink
Ive been using the Doefer A-125 phase shifter to produce classic phase modulation effects to great effect. It does sound a bit different from true PM and not as deep as say a hertz donut mk2 but its in the same sonic realm and much cleaner and more versatile than folding options like FM Aid. The Plaits harmonic oscillator with pseudo phase mod is mind blowing!
perhaps a frequency shifter might work better. I've had some success using the fsh1 to get the pm effect at non audio rate levels. I haven't tried with higher rates.
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