Hello Darryl,
you wrote:
> I’m trying to simulate a square wave signal. So far I have this,
> which should be a 400Hz square wave.
> play -V -r48000 -n synth square 400 0 0
This looks quite realistic to me.
> Is there
> 1. A way to make the amplitude rise and fall over time?
This is easy: you can either use another synth modulation or a tremolo:
play -r48000 -n synth square 400 0 0 synth sine amod 0.5
or
play -r48000 -n synth square 400 0 0 tremolo 0.5 50
where tremolo also allows to set the modulation depth via its second
parameter.
> 2. Vary the duty cycle over time, from say 300Hz to 600Hz and back down
> to 300Hz then repeat?
I am not sure whether you mean a pulse width modulation or a frequency
modulation (the latter sounds like a frequency modulation...)? In
principle some sort of frequency modulation is possible via fmod instead
of amod above, but it is a double-sideband suppressed-carrier amplitude
modulation and not a real frequency modulation as you request.
I do not know of a genuine frequency modulation in real-time.
But when real-time is not required, you could define a sweep parameter
for the synth like e.g.
sox -r 48000 -n part1.wav synth 5 square 300-600
sox -r 48000 -n part2.wav synth 5 square 600-300
play part1.wav part2.wav
The kind of sweep can be specified by giving either '+' '-' '/' or ':'
as the separator between frequencies.
Hope this helps!
Best regards,
Thomas
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