A theoretical introduction into amplitude-modulation, ringmodulation and waveshaping is given in the "sound-synthesis" chapter 4.
In "sound-synthesis" the principle of AM was shown as a amplitude multiplication of two sine oscillators. Later we've used a more complex modulators, to generate more complex spectrums. The principle also works very well with sound-files (samples) or live-audio-input.
Karlheinz Stockhausens "Mixtur für Orchester, vier Sinusgeneratoren und vier Ringmodulatoren” (1964) was the first piece which used analog ringmodulation (AM without DC-offset) to alter the acoustic instruments pitch in realtime during a live-performance. The word ringmodulation inherites from the analog four-diode circuit which was arranged in a "ring".
In the following example shows how this can be done digitally in Csound. In this case a sound-file works as the carrier which is modulated by a sine-wave-osc. The result sounds like old 'Harald Bode' pitch-shifters from the 1960's.
Example: 05F01.csd
<CsoundSynthesizer> <CsOptions> -o dac </CsOptions> <CsInstruments> sr = 48000 ksmps = 32 nchnls = 1 0dbfs = 1 instr 1 ; Ringmodulation aSine1 poscil 0.8, p4, 1 aSample diskin2 "fox.wav", 1, 0, 1, 0, 32 out aSine1*aSample endin </CsInstruments> <CsScore> f 1 0 1024 10 1 ; sine i 1 0 2 400 i 1 2 2 800 i 1 4 2 1600 i 1 6 2 200 i 1 8 2 2400 e </CsScore> </CsoundSynthesizer> ; written by Alex Hofmann (Mar. 2011)
coming soon..