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Diffstat (limited to 'third_party/resample/src/windowfilter.c')
| -rw-r--r-- | third_party/resample/src/windowfilter.c | 114 |
1 files changed, 0 insertions, 114 deletions
diff --git a/third_party/resample/src/windowfilter.c b/third_party/resample/src/windowfilter.c deleted file mode 100644 index b2b67690..00000000 --- a/third_party/resample/src/windowfilter.c +++ /dev/null @@ -1,114 +0,0 @@ -/* makefilter.c */ - -#include <stdio.h> -#include <math.h> -#include "stdefs.h" -#include "filterkit.h" -#include "resample.h" -#define MAXNWING 8192 /* FIXME: flush */ - -/* LIBRARIES needed: - * - * 1. filterkit - * makeFilter() - designs a Kaiser-windowed low-pass filter - * writeFilter() - writes a filter to a standard filter file - * GetUShort() - prompt user for a UHWORD with help - * GetDouble() - prompt user for a double with help - * - * 2. math - */ - -char NmultHelp[] = - "\n Nmult is the length of the symmetric FIR lowpass filter used" - "\n by the sampling rate converter. It must be odd." - "\n This is the number of multiplies per output sample for" - "\n up-conversions (Factor>1), and is the number of multiplies" - "\n per input sample for down-conversions (Factor<1). Thus if" - "\n the rate conversion is Srate2 = Factor*Srate1, then you have" - "\n Nmult*Srate1*MAXof(Factor,1) multiplies per second of real time." - "\n Naturally, higher Nmult gives better lowpass-filtering at the" - "\n expense of longer compute times. Nmult should be odd because" - "\n it is the length of a symmetric FIR filter, and the current" - "\n implementation requires a coefficient at the time origin.\n"; - -char FrollHelp[] = - "\n Froll determines the frequency at which the lowpass filter begins to" - "\n roll-off. If Froll=1, then there is no 'guard zone' and the filter" - "\n roll-off region will be aliased. If Froll is 0.90, for example, then" - "\n the filter begins rolling off at 0.90*Srate/2, so that by Srate/2," - "\n the filter is well down and aliasing is reduced. Since aliasing" - "\n distortion is typically worse than loss of the high-frequency spectral" - "\n amplitude, Froll<1 is highly recommended. The default of 0.90" - "\n sacrifices the upper 10 percent of the spectrum as an anti-aliasing" - "\n guard zone.\n"; - -char BetaHelp[] = - "\n Beta trades the rejection of the lowpass filter against the" - "\n transition width from passband to stopband. Larger Beta means" - "\n a slower transition and greater stopband rejection. See Rabiner" - "\n and Gold (Th. and App. of DSP) under Kaiser windows for more about" - "\n Beta. The following table from Rabiner and Gold (p. 101) gives some" - "\n feel for the effect of Beta:" - "\n" - "\n BETA D PB RIP SB RIP" - "\n 2.120 1.50 +-0.27 -30" - "\n 3.384 2.23 0.0864 -40" - "\n 4.538 2.93 0.0274 -50" - "\n 5.658 3.62 0.00868 -60" - "\n 6.764 4.32 0.00275 -70" - "\n 7.865 5.0 0.000868 -80" - "\n 8.960 5.7 0.000275 -90" - "\n 10.056 6.4 0.000087 -100" - "\n" - "\n Above, ripples are in dB, and the transition band width is " - "\n approximately D*Fs/N, where Fs = sampling rate, " - "\n and N = window length. PB = 'pass band' and SB = 'stop band'." - "\n Alternatively, D is the transition widths in bins given a" - "\n length N DFT (i.e. a window transform with no zero padding." - "\n"; - - -int main(void) -{ - HWORD Imp[MAXNWING]; /* Filter coefficients */ - HWORD ImpD[MAXNWING]; /* ImpD[i] = ImpD[i+1] - ImpD[i] */ - double Froll, Beta; - UHWORD Nmult, Nwing, LpScl; - int err; - - Froll = 0.90; - Beta = 9; - Nmult = 65; - while (1) - { - Froll = GetDouble("Normalized Roll-off freq (0<Froll<=1)", - Froll, FrollHelp); - Beta = GetDouble("Beta", Beta, BetaHelp); - Nmult = GetUHWORD("Odd filter length 'Nmult'", Nmult, NmultHelp); - if ((Nmult&1) == 0) { - Nmult++; - printf("Filter length increased to %d to make it odd.\n",Nmult); - } - Nwing = Npc*(Nmult-1)/2; /* # of filter coeffs in right wing */ - printf("\n"); - if (!(Nmult % 2)) - printf("Error: Nmult must be odd and greater than zero\n"); - else if ((err = makeFilter(Imp, ImpD, &LpScl, Nwing, Froll, Beta))) { - printf("*** Error: Unable to make filter.\n"); - if (err == 1) - printf("\tNmult=%d too large for MAXNWING=%d\n",Nmult,MAXNWING); - else if (err == 2) - printf("\tNormalized roll-off freq Froll must be between 0 and 1\n"); - else if (err == 3) - printf("\tHeisenberg says Beta must be greater or equal to 1\n"); - else if (err == 4) { - printf("\tUnity-gain scale factor overflows 16-bit half-word\n"); - printf("\tFilter design was probably way off. Try relaxing specs.\n"); - } - } else if ((err = writeFilter(Imp, ImpD, LpScl, Nmult, Nwing))) - printf("Error: Unable to write filter, err=%d\n", err); - else - break; - } - return(0); -} |