| Message ID | CAG5mAdzweX=mEPE+eHSeYhoutiY=0zpZ8kH3ttBiZ0WiypAFCQ@mail.gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, 2015-09-18 at 09:50 -0700, Caleb Crome wrote: > Hi Han, Liam, all, > > It looks like you have run into the old problem that the math library > actually stinks at generating sine waves right :-) > > > + for (k = 0; k < length; k++) { > > + for (c = 0; c < bat->channels; c++) { > > + idx = k * bat->channels + c; > > + out[idx] = sinf(val[c] * i) * factor; > > + } > > + i++; > > + if (i == bat->rate) > > + i = 0; /* Restart from 0 after one sine wave period */ > > + } > > If I'm reading this right, you're resetting the argument to the sinf > function. This can generate unwanted distortion in the sine wave if > the frequency isn't an exact fraction of the sample rate. > > Here's a little library (along with a test program) I just whipped up > using a phasor as the sine wave generator. > The test program runs it for a simulated 3 days, then prints a python > script to stdout that you can then run and plot to see the generated > wave. > > This will work for any frequency sine wave, and as far as I know, it's > the best way to generate sine waves. (Not for calculating the sin of a > value though!) > > Here is the generator and test program. Sorry If this isn't the right > way to submit a file/patch, but I have no idea how to do it properly > :-/ > No worries, I dont think Han has put a link to his public git repo so it will be a bit more difficult to create proper patches. > BTW, this isn't actually integrated into the bat program, it's just > the little library for generating the sine waves. > Thanks, we can integrate and add to the codebase for resending V2 patches. :) Liam > Author: Caleb Crome <caleb@signalessence.com> > Date: Fri Sep 18 09:45:43 2015 -0700 > > added sin_generator > > diff --git a/bat/sin_generator.c b/bat/sin_generator.c > new file mode 100644 > index 0000000..e67f376 > --- /dev/null > +++ b/bat/sin_generator.c > @@ -0,0 +1,120 @@ > +#include "math.h" > +#include "sin_generator.h" > +/* > + * Copyright (C) 2015 Caleb Crome > + * > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License as published by > + * the Free Software Foundation; either version 2 of the License, or > + * (at your option) any later version. > + * > + * This program is distributed in the hope that it will be useful, > + * but WITHOUT ANY WARRANTY; without even the implied warranty of > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > + * GNU General Public License for more details. > + * > + */ > + > +/* > + * This is a general purpose sine wave generator that will stay stable > + * for a long time, and with a little renormalization, could stay stay > + * stable indefinitely > + */ > + > + > +/* Initialize the sine wave generator. > + * sin_generator: gets initialized by this call. > + * frequency: the frequency for the sine wave. must be < 0.5*sample_rate > + * sample_rate: the the sample rate... > + * returns 0 on success, -1 on error. > + */ > +int sin_generator_init(struct sin_generator *sg, float magnitude, > float frequency, float sample_rate) > +{ > + // angular frequency: cycles/sec / (samp/sec) * rad/cycle = rad/samp > + float w = frequency/sample_rate*2*M_PI; > + if (frequency >= sample_rate/2) > + return -1; > + sg->phasor_real = cos(w); > + sg->phasor_imag = sin(w); > + sg->magnitude = magnitude; > + sg->state_real = 0.0; > + sg->state_imag = magnitude; > + sg->frequency = frequency; > + sg->sample_rate = sample_rate; > + return 0; > +} > + > +/* > + * Generates the next sample in the sine wave. > + * should be much faster than calling a sin function > + * if it's inlined and optimized. > + * > + * returns the next value. no possibility of error. > +*/ > +float sin_generator_next_sample(struct sin_generator *sg) > +{ > + // get shorthand to pointers > + const double pr = sg->phasor_real; > + const double pi = sg->phasor_imag; > + const double sr = sg->state_real; > + const double si = sg->state_imag; > + // step the phasor -- complex multiply > + sg->state_real = sr * pr - si * pi; > + sg->state_imag = sr * pi + pr * si; > + return sr; // return the input value so sine wave starts at > + // exactly 0.0 > +} > +/* fills a vector with a sine wave */ > +void sin_generator_vfill(struct sin_generator *sg, float *buf, int n) > +{ > + int i; > + for (i = 0; i < n; i++) { > + *buf++ = sin_generator_next_sample(sg); > + } > +} > + > +#ifdef TEST_PHASOR > +#define TESTSIZE (48000/1000) > +// compile with this command to create executable that will > +// auto-generate a self plotting plot :-) > + > +// gcc -g sin_generator.c -o sin_generator -lm -DTEST_PHASOR > + > +#include <stdio.h> > + > +void dumpbuffer(const char *name, float *buffer, int n) > +{ > + int i; > + printf("%s = [\n", name); > + for (i = 0; i < n; i++) { > + printf(" %f,\n", buffer[i]); > + } > + printf("]\n"); > + printf("plot(%s)\n", name); > +} > + > +int main(int argc, char *argv[]) > +{ > + float buffer[TESTSIZE]; > + long int i; > + struct sin_generator sg; > + > + // test the first few. > + sin_generator_init (&sg, 3.0, 1000, 48000); > + sin_generator_vfill(&sg, buffer, TESTSIZE); > + printf("from pylab import *\n"); > + dumpbuffer("s", buffer, TESTSIZE); > + > + // now wind the phasor for 3 days worth of samples to see > + // if magnitude drifts. > + for (i = 0; i < (3L*24*60*60*48000); i++) > + sin_generator_next_sample(&sg); > + > + sin_generator_vfill(&sg, buffer, TESTSIZE); > + // and let's see what that one looks like > + dumpbuffer("o", buffer, TESTSIZE); > + printf("show()\n"); > + > + return 0; > +} > +#endif > diff --git a/bat/sin_generator.h b/bat/sin_generator.h > new file mode 100644 > index 0000000..2ab7561 > --- /dev/null > +++ b/bat/sin_generator.h > @@ -0,0 +1,23 @@ > +/* > + * Here's a generic sine wave generator that will work indefinitely > for any frequency. > + * > + * Note: the state & phasor are stored as doubles (and updated as > + * doubles) because after a million samples the magnitude drifts a > + * bit. If we really need floats, it can be done with periodic > + * renormalization of the state_real+state_imag magnitudes. I was > + */ > + > +struct sin_generator; > +struct sin_generator { > + double state_real; > + double state_imag; > + double phasor_real; > + double phasor_imag; > + float frequency; > + float sample_rate; > + float magnitude; > +}; > + > +int sin_generator_init(struct sin_generator *sg, float magnitude, > float frequency, float sample_rate); > +float sin_generator_next_sample(struct sin_generator *sg); > +void sin_generator_vfill(struct sin_generator *sg, float *buf, int n);
diff --git a/bat/sin_generator.c b/bat/sin_generator.c new file mode 100644 index 0000000..e67f376 --- /dev/null +++ b/bat/sin_generator.c @@ -0,0 +1,120 @@ +#include "math.h" +#include "sin_generator.h" +/* + * Copyright (C) 2015 Caleb Crome + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + */ + +/* + * This is a general purpose sine wave generator that will stay stable + * for a long time, and with a little renormalization, could stay stay + * stable indefinitely + */ + + +/* Initialize the sine wave generator. + * sin_generator: gets initialized by this call. + * frequency: the frequency for the sine wave. must be < 0.5*sample_rate + * sample_rate: the the sample rate... + * returns 0 on success, -1 on error. + */ +int sin_generator_init(struct sin_generator *sg, float magnitude, float frequency, float sample_rate) +{ + // angular frequency: cycles/sec / (samp/sec) * rad/cycle = rad/samp + float w = frequency/sample_rate*2*M_PI; + if (frequency >= sample_rate/2) + return -1; + sg->phasor_real = cos(w); + sg->phasor_imag = sin(w); + sg->magnitude = magnitude; + sg->state_real = 0.0; + sg->state_imag = magnitude; + sg->frequency = frequency; + sg->sample_rate = sample_rate; + return 0; +} + +/* + * Generates the next sample in the sine wave. + * should be much faster than calling a sin function + * if it's inlined and optimized. + * + * returns the next value. no possibility of error. +*/ +float sin_generator_next_sample(struct sin_generator *sg) +{ + // get shorthand to pointers + const double pr = sg->phasor_real; + const double pi = sg->phasor_imag; + const double sr = sg->state_real; + const double si = sg->state_imag; + // step the phasor -- complex multiply + sg->state_real = sr * pr - si * pi; + sg->state_imag = sr * pi + pr * si; + return sr; // return the input value so sine wave starts at + // exactly 0.0 +} +/* fills a vector with a sine wave */ +void sin_generator_vfill(struct sin_generator *sg, float *buf, int n) +{ + int i; + for (i = 0; i < n; i++) { + *buf++ = sin_generator_next_sample(sg); + } +} + +#ifdef TEST_PHASOR +#define TESTSIZE (48000/1000) +// compile with this command to create executable that will +// auto-generate a self plotting plot :-) + +// gcc -g sin_generator.c -o sin_generator -lm -DTEST_PHASOR + +#include <stdio.h> + +void dumpbuffer(const char *name, float *buffer, int n) +{ + int i; + printf("%s = [\n", name); + for (i = 0; i < n; i++) { + printf(" %f,\n", buffer[i]); + } + printf("]\n"); + printf("plot(%s)\n", name); +} + +int main(int argc, char *argv[]) +{ + float buffer[TESTSIZE]; + long int i; + struct sin_generator sg; + + // test the first few. + sin_generator_init (&sg, 3.0, 1000, 48000); + sin_generator_vfill(&sg, buffer, TESTSIZE); + printf("from pylab import *\n"); + dumpbuffer("s", buffer, TESTSIZE); + + // now wind the phasor for 3 days worth of samples to see + // if magnitude drifts. + for (i = 0; i < (3L*24*60*60*48000); i++) + sin_generator_next_sample(&sg); + + sin_generator_vfill(&sg, buffer, TESTSIZE); + // and let's see what that one looks like + dumpbuffer("o", buffer, TESTSIZE); + printf("show()\n"); + + return 0; +} +#endif diff --git a/bat/sin_generator.h b/bat/sin_generator.h new file mode 100644 index 0000000..2ab7561 --- /dev/null +++ b/bat/sin_generator.h @@ -0,0 +1,23 @@ +/* + * Here's a generic sine wave generator that will work indefinitely for any frequency. + * + * Note: the state & phasor are stored as doubles (and updated as + * doubles) because after a million samples the magnitude drifts a + * bit. If we really need floats, it can be done with periodic + * renormalization of the state_real+state_imag magnitudes. I was + */ + +struct sin_generator; +struct sin_generator { + double state_real; + double state_imag; + double phasor_real; + double phasor_imag; + float frequency; + float sample_rate; + float magnitude; +}; + +int sin_generator_init(struct sin_generator *sg, float magnitude, float frequency, float sample_rate);