38 lines
1.1 KiB
C++
38 lines
1.1 KiB
C++
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/* IIR filter
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Fp = 20000.62
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os = 6; N = 8*2; Gp = 0.0135; Gs = 120;
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overall delay: ~5 samples
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*/
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#define BQSHIFT(i) \
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h[i*2 + 1] = h[i*2 + 0]; \
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h[i*2 + 0] = x;
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// b0 and b2 are equivalent and factored out
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// b0 and a0 are factored out as overall gain
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#define LOWPASS(i, b1, a1, a2) \
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y = x + b1*h[i*2 + 0] + h[i*2 + 1] \
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- a1*h[i*2 + 2] - a2*h[i*2 + 3]; \
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BQSHIFT(i); \
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x = y;
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static double
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oversample(double *h, double x)
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{
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// h[] should be at least 18 doubles long
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double y;
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LOWPASS(0,-1.7310964991540,-1.7686201550064,+0.9924894080401);
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LOWPASS(1,-1.7228987922703,-1.7591070571963,+0.9756664940293);
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LOWPASS(2,-1.7030928294094,-1.7508784553758,+0.9530819894740);
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LOWPASS(3,-1.6623628189757,-1.7420481292930,+0.9206849371458);
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LOWPASS(4,-1.5767803723821,-1.7314029454409,+0.8755898544307);
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LOWPASS(5,-1.3754954625889,-1.7189289035735,+0.8193999703446);
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LOWPASS(6,-0.7934216412437,-1.7066722500921,+0.7627918423024);
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LOWPASS(7,+1.1176227011686,-1.6987049565355,+0.7256338727337);
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BQSHIFT(8);
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return y*0.000005162322938;
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}
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#undef BQSHIFT
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#undef LOWPASS
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