---------------------------- Original Message ---------------------------- Subject: Re: [music-dsp] Time-variant 2nd-order sinusoidal resonator From: "Andrew Simper" <a...@cytomic.com> Date: Wed, February 20, 2019 9:20 pm To: "Robert Bristow-Johnson" <r...@audioimagination.com> "A discussion list for music-related DSP" <music-dsp@music.columbia.edu> -------------------------------------------------------------------------- > This looks pretty good to me, and I like the amplitude adjustment g[n] term > :) well, then let's integrate that into your code. > > Depending on the situation you may want to modulate the frequency of the > oscillator pretty fast, so it can help to use a tan approximation function > and then a division and a few other operations to get your cos (w) and sin > (w) rotation terms from that single approximation. I've called the rotation > terms g0 and g1, and c and s are the output cos and sin quadrature > oscillator values > > init: > c = cos(2*pi*startphase) > s = sin(2*pi*startphase) � �gain = 1 � �adaptationspeed = 0.5� � �// this could be made smaller, but must be positive > > set frequency: > g0 = cos(2*pi*frequency/samplerate) > g1 = sin(2*pi*frequency/samplerate) > > or > > g = tan(pi*frequency/samplerate); > gg = 2/(1 + g*g) > g0 = gg-1 > g1 = g*gg > > tick: > t0 = g0*c - g1*s > t1 = g1*c + g0*s � c = gain*t0 � s = gain*t1 � gain = 1 + adaptationspeed*(1 - c*c - s*s) � -- r b-j� � � � � � � � � � � � �r...@audioimagination.com "Imagination is more important than knowledge." � � � �
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