Thoughts About Ring Modulation

Ring Modulation is easy to make technique in a program such as Max/MSP that yields fun and interesting results.  This sound synthesis technique uses a bi-polar modulation signal.  The frequencies produced can be calculated by saying Carrier Frequency + Modulation Frequency and Carrier Frequency – Modulation Frequency

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Even When the modulation frequency is below 20 Hz  the C+M and C-M frequencies are produced but are critical bands because they are perceived as a beating pattern and not two separate signals.  In the above example the two frequencies are 439 and 441.  They are close enough together to produce a pulse without much change in pitch.

Now the modulator is 2000 Hz.  Two distinct pitches are produced at 2440 and 1560. This relationship will always occur until two distinct pitches are heard that seem to not influence one another.

With complex sounds the result is more interesting.  When the modulation frequency is higher than 20 Hz each frequency in the sound will produce 2 frequencies in the C+M and C-M relationship.

This shows a regular square wave with the modulation frequency of 1 Hz.  It looks like a regular square and the C+M, C-M relationship is not seen because the frequencies are too close.

Now that the modulation frequency is 2000 Hz each frequency in the square is producing 2 frequencies and the spectrum doubles in size and the sound changes.

Ring modulation can be used live as well to create vibrato and also exploited (modulator with higher frequencies) to alter the sound drastically and create interesting pitch relationships.