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# File 'lib/audio_stream/fx/low_shelf_filter.rb', line 5
def update_coef(freq:, q:, gain:)
if Decibel===gain
gain = gain.db
end
omega = 2.0 * Math::PI * freq / @samplerate
alpha = Math.sin(omega) / (2.0 * q)
a = 10.0 ** (gain / 40.0)
beta = Math.sqrt(a) / q
a0 = (a+1) + (a-1) * Math.cos(omega) + beta * Math.sin(omega)
a1 = -2.0 * ((a-1) + (a+1) * Math.cos(omega))
a2 = (a+1) + (a-1) * Math.cos(omega) - beta * Math.sin(omega)
b0 = a * ((a+1) - (a-1) * Math.cos(omega) + beta * Math.sin(omega))
b1 = 2.0 * a * ((a-1) - (a+1) * Math.cos(omega))
b2 = a * ((a+1) - (a-1) * Math.cos(omega) - beta * Math.sin(omega))
@coef = Vdsp::Biquad::Coefficient.new(b0/a0, b1/a0, b2/a0, a1/a0, a2/a0)
@biquads.each {|biquad|
biquad.coefficients = @coef
}
end
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