Re: Vary the volume and duty cycle over time

["Dr. Thomas Tensi" <t.tensi@gmx.de>]

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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