[chuck-users] pulse width modulation
Hans Aberg
haberg at math.su.se
Mon Feb 8 04:23:35 EST 2010
On 8 Feb 2010, at 04:12, Andrew C. Smith wrote:
> You'll want to use PulseOsc instead of SqrOsc. When they say "square
> wave tone" they probably mean the squared-off edges. Basically, a
> pulse width of 0.5 would be a "square" wave, while 0.2 would be a
> much shorter impulse. I'm not sure what the exact spectral content
> of the different pulse widths are, though.
A Fourier coefficients tables say that for pulse width factor k, the
series is the sum of b_i*sin(i*w*t), i = 1, 2, ..., the angular
frequency w = 2*pi*f, f the frequency, and
b_i = 4*A*sin(i*pi*k)/i*pi
where A is the amplitude (half distance between max and min). So for k
= 1/2, one just gets odd partials of relative amplitude 1/i, but when
distorted the whole spectrum starts to show up.
Hans
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