Bipolar or Unipolar Modulator in Ring Modulation ?

Quote: Cheng Chien-Wen wrote on Thu, 28 August 2008 15:52
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> In ring modulation patches, I have noticed that some people use the windowing function to make the signal from modulator all positive instead of orginal alternation of positive and negative values. I did some experiments with both and found that the resulted sound with bipolar modulator "vibrates" twice faster as the one with unipolar modulator but don't know why.
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> Could any one let me know the purpose of making unipolar modulator in ring modulation patches instead of bipolar ?
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> I also would like to know what happens with the carrier signal when the signal value of modulator goes below 0. Please explain.
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> Thank you so much.
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Ok, let's see.. How was it again...

Ring modulation is a form of amplitude modulation. AM can be done with either unipolar or bipolar signals. The term RM is more or less reserved for amplitude modulation with audiorate (>20Hz) bipolar signals. If you do AM with a slower bipolar signal, it will just be perceived as AM with a unipolar signal, but modulating twice as fast. So you modulate with a 5Hz bipolar sine, but you hear a 10 Hz modulation.

An important difference between modulating with unipolar and bipolar signals at faster rates it that the original signal disappears with bipolar and you'll hear only the sidebands.

So, RM is a form of AM. We normally call it AM when using either slow or fast unipolar signals for a modulator, and RM when using a fast bipolar modulator. There is no reason to use slow bipolar modulators, it is more convenient to use unipolar for slow modulation since then the perceived mod freq will be equal to the frequency of the modulating oscillator.

Hope this helps?
Fellow maxers please correct where I messed/mixed something up - this was typed in a hurry.

regards,
kjg