Ring Modulator is not ring modulating

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honki-bobo
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Ring Modulator is not ring modulating

Post by honki-bobo »

I was using the Cherry Audio Ring Modulator module today and I found that it actually isn't ring modulating.

From what I understand, a ring modulator takes two input signals x(t) and y(t) and outputs z(t) = x(t) * y(t), but the Ring Modulator module definitely has a different output.

signals.jpg
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Frequency-wise (if the input is a sine wave) a ring modulator should output the sum and the difference of the frequencies of the input. This isn't happening, either.

frequencies.jpg
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Correct me if I'm wrong or if I'm missing something here, but the Ring Modulator module does not actually ring modulate the input signals. And I haven't found anything special being mentioned in the documentation at https://docs.cherryaudio.com/cherry-aud ... -modulator.

Best regards,
Martin
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huggermugger
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Re: Ring Modulator is not ring modulating

Post by huggermugger »

Agreed. Whatever their RingMod is doing, it's not ring modulation. Two sinewaves should produce a similarly pure, dull tone when ring modded, not that buzzy, overdriven sound that RingMod produces.

I tested a few ring modulators in VCV Rack, and generally got the expected results, although three of them (the three on the bottom) didn't retain the sine wave purity, perhaps I just don't know how to use them properly.
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UrbanCyborg
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Re: Ring Modulator is not ring modulating

Post by UrbanCyborg »

I wondered about this, too. Maybe they've just tapped into the confusion there seems to be in general about what a ring modulator is, and coded up something that does what one of the "musical" interpretations has it to be. I do notice that elsewhere in the docs there's some confusion about just what AM and FM do (in the description of FM, as I recall), although I don't think in that instance the code actually does the wrong thing.
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ColinP
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Re: Ring Modulator is not ring modulating

Post by ColinP »

Well spotted Martin.

It's a bit weird as the code for true ring modulation is utterly simple. Yet CA seem to have made it complicated by adding a non-linear transfer curve.

To get true ring modulation just use the Formula module and enter the formula x*y.

I knocked up the following patch to compare the waveforms and sounds.

The green trace shows ring modulation.

The cyan trace shows CA's Ring Modulator output.
ringmod trial.png
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Cherryaudio Danny
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Re: Ring Modulator is not ring modulating

Post by Cherryaudio Danny »

Hello,

The Cherry Audio Ring Modulator essentially multiplies the signals together as expected. For example, feeding +2v and -2v into the ring modulator outputs -4 volts. However, as you'd find in hardware, there is a maximum voltage range of -5 to +5 volts. The ring modulator will distort as you approach the maximum voltage range, which is a part of its character and sound.

If a 'true' ring modulator is desired, attenuating the voltage range to be around or below -4 to +4 volts to avoid engaging the distortion will do the trick!


Danny
anonyrat
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Re: Ring Modulator is not ring modulating

Post by anonyrat »

Looking at the CA blue line I think it should be called a drum modulator. Anyone else see drum music there - bum.titty.Bum.titty ? 😁
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honki-bobo
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Re: Ring Modulator is not ring modulating

Post by honki-bobo »

Cherryaudio Danny wrote: Tue Feb 01, 2022 8:58 pm For example, feeding +2v and -2v into the ring modulator outputs -4 volts.
Sorry, but no, it doesn't. If I feed it -2V on the x input and 2V on the y input, it outputs about -3.1241267V when both "levels" are set to 50% (which is the default) and -4.06798014V when they are set to 100%.

I also get the same "distorted" output when I scale the oscillator signals down to -1..1V with an Attenuverter set to 20% and it also doesn't make a difference if I use the "Level" knobs directly.
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Cherryaudio Danny
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Re: Ring Modulator is not ring modulating

Post by Cherryaudio Danny »

Hello,

Interesting. I'll reproduce and log a bug report if that's the case. By design, I believe it's supposed to be 'pure' until the threshold mentioned.
Thanks for taking the time to look into this!

Danny
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honki-bobo
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Re: Ring Modulator is not ring modulating

Post by honki-bobo »

Thanks, Danny, for passing this to the developers.

FWIW, I found that if I set the levels to 0.01 % and scale the output back up by about 120 db I get the expected ring modulation results.

ringmod_with_scaling.jpg
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Steve W
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Re: Ring Modulator is not ring modulating

Post by Steve W »

Interesting effect as two sine waves go in and out of phase.
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Last edited by Steve W on Wed Feb 02, 2022 2:58 pm, edited 5 times in total.
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