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Move library tree where it belongs
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ra
144
lib-src/libnyquist/nyquist/tran/pluck.alg
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144
lib-src/libnyquist/nyquist/tran/pluck.alg
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;; PLUCK.ALG is based on the Pluck.t instrument from M4C
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;;
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; to assist with debugging, here are some calculated parameters
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; dumped from a run of M4C:
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;
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; Setup Pluck at t= 6.000
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; DUR= 1.000, pitch= 8.060, amp= 10000, DB_drop= 60.0, rfrac=0.00
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; freq 369.995
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; freq = 369.995361
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; Final = 1000.000000, t= 0.052715, y = 0.000000, lF = 6.907755
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; tdecay = 13.430565, sT = 369.995361, rho = 0.982869, stretch = 0.500000
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; N = 59, x = 0.095342, cons = 0.825914
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; x2 0.412957 x3 0.912957 stretch 0.5 cons 0.825914 SR 22050
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; complete Pluck setup
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;;
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(PLUCK-ALG
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(NAME "pluck")
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(ARGUMENTS ("rate_type" "sr") ("double" "hz") ("time_type" "t0")
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("time_type" "d") ("double" "final_amp"))
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(SUPPORT-FUNCTIONS "
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#define MAXLENGTH 20000
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long pluck_parameters(double hz, double sr, double final, double dur,
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double *stretch, double *cons, double *rho)
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{
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double t = PI * (hz / sr);
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double y = fabs(cos(t));
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/* original m4c code used ratio of initial amp to final amp in dB
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and then converted to a ratio, e.g. you specify 60 and the
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parameter Final is 1000.0. This is counterintuitive to me (RBD)
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because I would expect the value to be -60dB or 0.001. That is
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what I implemented, so to get this back into correspondence
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with the m4c algorithm, I take the NEGATIVE log to get lf,
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whereas m4c takes the positive log:
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*/
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double lf = -log(final);
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double tdecay = -lf / (hz * log(y));
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double st;
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long len;
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double x;
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if (hz <= sr / MAXLENGTH) {
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xlfail(\"pluck hz is too low\");
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} else if (hz >= sr / 3) {
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xlfail(\"pluck hz is too high\");
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}
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/*
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* if desired decay time is shorter than the natural decay time,
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* then introduce a loss factor. Otherwise, stretch note out.
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*/
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st = hz * dur;
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if (dur < tdecay) {
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*rho = exp(-lf / st) / y;
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*stretch = 0.5;
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} else {
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*rho = 1;
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*stretch = 0.5 + sqrt(0.25 -
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(1 - exp(2 * lf * (hz - sr) / (st * sr))) /
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(2 - 2 * cos(2 * t)));
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}
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/* delay line length is */
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len = (int) ((sr / hz) - *stretch - 0.001);
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/* tuning constant is */
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x = (sr / hz) - len - *stretch;
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*cons = (1.0 - x) / (1.0 + x);
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if (len <= 1) {
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xlfail(\"internal error: pluck delay line length too short\");
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}
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return len;
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}
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static unsigned int rnext = 1;
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int krand()
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{
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rnext = rnext * 1103515245 + 12345;
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return (rnext >> 16) & 0x7fff;
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}
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void pluck_initialize(sample_type *shiftreg, sample_type *array,
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long len, double cons)
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{
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sample_type suma = 0.0F;
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long k;
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sample_type avea;
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array[1] = 0;
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for (k = len; k > 0; k--, array--) {
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/* note: the m4c code has a bug. It claims to filter
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the initial values, but it really just sets the
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values to +1 or -1. The following does the same
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thing with much less code:
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*/
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*array = (krand() & 2) - 1;
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suma += *array; /* compute sum for the average */
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}
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avea = suma / len;
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/* zero the average */
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for (k = 0; k <= len + 1; k++) shiftreg[k] -= avea;
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shiftreg[len] = 0;
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shiftreg[len + 1] = 0;
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}")
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(STATE ("double" "stretch" "0")
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("double" "cons" "0")
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("double" "loss" "0")
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("long" "len" "pluck_parameters(hz, sr, final_amp, d,
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&susp->stretch, &susp->cons,
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&susp->loss)")
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("double" "x2" "-susp->cons * (susp->stretch - 1)")
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("double" "x3" "susp->cons * susp->stretch - susp->stretch + 1")
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("sample_type *" "shiftreg"
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;; I think susp->len + 2 is the correct value, but I use +4 to be safe
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"(sample_type *) calloc (susp->len + 4, sizeof(sample_type))")
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("sample_type *" "i1" "susp->shiftreg + susp->len + 1")
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("sample_type *" "i2" "susp->shiftreg + susp->len")
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("sample_type *" "i3" "susp->shiftreg + susp->len - 1")
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("sample_type *" "i4" "susp->shiftreg + susp->len - 2")
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("sample_type *" "endptr" "susp->shiftreg + susp->len + 2;
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pluck_initialize(susp->shiftreg, susp->i3,
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susp->len, susp->cons)"))
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(CONSTANT "stretch" "cons" "loss" "len" "x2" "x3" "endptr")
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(SAMPLE-RATE "sr")
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(NOT-REGISTER shiftreg)
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(TERMINATE (AFTER "d"))
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(INNER-LOOP " sample_type sum = (sample_type)
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((*i1++ * x2) + (*i2++ * x3) +
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(*i3++ * stretch) - (*i4++ * cons));
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/* wrap pointers around shift register if necessary */
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if (i1 == endptr) i1 = susp->shiftreg;
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if (i2 == endptr) i2 = susp->shiftreg;
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if (i3 == endptr) i3 = susp->shiftreg;
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if (i4 == endptr) i4 = susp->shiftreg;
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/* store new value in shift register */
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*i4 = (sample_type) (sum * loss);
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/* deliver sample */
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output = sum;
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")
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(FINALIZATION " free(susp->shiftreg);\n")
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)
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