"Prior art synthesizers often select a small interval d to detune. For
example, if the nominal oscillator frequency was 1000 Hz, then applying
a detune parameter of 10 cent would result in a detuned oscillator
frequency of 1006 Hz. However, at the next octave, the nominal frequency
would be 2000 Hz with the detuned oscillator frequency of 2012 Hz.
Accordingly, a detuned oscillator has a frequency deviation which is
proportional to its nominal frequency. Hence, when mixing detuned
oscillators, the resulting signal has a beat frequency which varies with
the pitch and doubles with each octave. An aim of the present invention
is to provide a music synthesizer whereby sounds are generated with a
constant optimum beat across a large range of tones.The present
invention relates to a music synthesizer comprising a first and second
oscillator and a signal generator which applies a constant
beat parameter to a pitch signal to derive the input for said second
oscillator, thereby enabling a synthesizer output to be generated at a
substantially constant beat."
In Csound this can be done with the following highly abstruse and
non-obvious code:
a1 oscil 1, ipch, 1
a2 oscil 1, ipch + 3, 1
amix = a1 + a2
Or more generally, by amplitude-modulating with an LFO at e.g. 3Hz.
So, what on earth are Apple up to here, trying to patent tremolo? Prior
Art? Decades...
Richard Dobson
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