Basic Synthesis: Subtractive, AM, FM, Waveshaping



This week we explored the production of harmonic and non-harmonic spectra using modulation synthesis techniques, specifically amplitude modulation (AM) and frequency modulation (FM).

Links

AM synthesis: FM synthesis:

Applications and Examples

Here are the AM and FM examples shown in class: The following is from a demo done for a potential landscape/soundscape project, showing a slightly more complex use of FM in a patch:


Both AM and FM work by creating spectral components using sidebands, or frequencies resulting from the modulation of the "carrier" oscillator by a "modulator" oscillator. The sideband components appear at the carrier frequency +/- integer multiples of the modulator frequency (see the tutorials above for a better explanation). The interesting thing is that this can work to produce non-harmonic spectra, always a fun thing to do! AM only produces a single set of sidebands -- FM produces a range of sidebands.

In our initial discussion of FM, we didn't do "real" frequency modulation, but instead did phase modulation. Shifting the phase while reading a wavetable oscillator is how we change the frequency of the oscillator, so essentially these two techniques are equivalent. There are some subtle differences, however, see the article by James McCartney above if you're interested. "fm3.pat" is a demonstration of actual FM.

We won't do subtractive synthesis until we get to the filter class, and I forgot about waveshaping. Silly me. We'll hit it later...