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FIR filter speedup, reduced memory usage

This commit is contained in:
SaucySoliton 2017-01-11 03:43:37 +00:00
parent 41c6523fc6
commit 81570e4733
1 changed files with 22 additions and 22 deletions
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42
src/fm_mpx.c
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@ -36,13 +36,12 @@
#define FIR_PHASES (32) #define FIR_PHASES (32)
#define FIR_SIZE (1024) // MUST be a power of 2 for the circular buffer #define FIR_TAPS (32) // MUST be a power of 2 for the circular buffer
#define FIR_TAPS (FIR_SIZE/FIR_PHASES)
size_t length; size_t length;
// coefficients of the low-pass FIR filter // coefficients of the low-pass FIR filter
float low_pass_fir[FIR_SIZE]; float low_pass_fir[FIR_PHASES][FIR_TAPS];
float carrier_38[] = {0.0, 0.8660254037844386, 0.8660254037844388, 1.2246467991473532e-16, -0.8660254037844384, -0.8660254037844386}; float carrier_38[] = {0.0, 0.8660254037844386, 0.8660254037844388, 1.2246467991473532e-16, -0.8660254037844384, -0.8660254037844386};
@ -61,8 +60,8 @@ int audio_index = 0;
int audio_len = 0; int audio_len = 0;
float audio_pos; float audio_pos;
float fir_buffer_left[FIR_SIZE] = {0}; float fir_buffer_left[FIR_TAPS] = {0};
float fir_buffer_right[FIR_SIZE] = {0}; float fir_buffer_right[FIR_TAPS] = {0};
int fir_index = 0; int fir_index = 0;
int channels; int channels;
float left_max=1, right_max=1; // start compressor with low gain float left_max=1, right_max=1; // start compressor with low gain
@ -140,9 +139,11 @@ int fm_mpx_open(char *filename, size_t len) {
b1=( 2.0*bp + 1/(in_samplerate*FIR_PHASES) )/(2.0*bp + 1/(in_samplerate*FIR_PHASES) ); b1=( 2.0*bp + 1/(in_samplerate*FIR_PHASES) )/(2.0*bp + 1/(in_samplerate*FIR_PHASES) );
double x=0,y=0; double x=0,y=0;
for(int i=1; i<=FIR_SIZE; i++) { // match indexing of Matlab script for(int i=0; i<FIR_TAPS; i++) {
sincpos = i-((FIR_SIZE+1.0)/2.0); // offset by 0.5 so sincpos!=0 (causes NaN x/0 ) for(int j=0; j<FIR_PHASES; j++) {
//printf("%d=%f ", i,sincpos); int mi=i*FIR_PHASES + j+1;// match indexing of Matlab script
sincpos = (mi)-(((FIR_TAPS*FIR_PHASES)+1.0)/2.0); // offset by 0.5 so sincpos!=0 (causes NaN x/0 )
//printf("%d=%f \n",mi ,sincpos);
firlowpass = sin(2 * PI * cutoff_freq * sincpos / (in_samplerate*FIR_PHASES) ) / (PI * sincpos) ; firlowpass = sin(2 * PI * cutoff_freq * sincpos / (in_samplerate*FIR_PHASES) ) / (PI * sincpos) ;
y=a0*firlowpass + a1*x + b1*y ; // Find the combined impulse response y=a0*firlowpass + a1*x + b1*y ; // Find the combined impulse response
@ -150,8 +151,9 @@ int fm_mpx_open(char *filename, size_t len) {
firpreemph=y; // y could be replaced by firpreemph but this firpreemph=y; // y could be replaced by firpreemph but this
// matches the example in the reference material // matches the example in the reference material
window = (.54 - .46 * cos(2*PI * (i) / (double) FIR_SIZE )) ; // Hamming window window = (.54 - .46 * cos(2*PI * (i) / (double) FIR_TAPS*FIR_PHASES )) ; // Hamming window
low_pass_fir[i-1] = firpreemph * window * gain ; // store with C indexing low_pass_fir[j][i] = firpreemph * window * gain ;
}
} }
printf("Created low-pass FIR filter for audio channels, with cutoff at %.1f Hz\n", cutoff_freq); printf("Created low-pass FIR filter for audio channels, with cutoff at %.1f Hz\n", cutoff_freq);
@ -159,10 +161,10 @@ int fm_mpx_open(char *filename, size_t len) {
if( 0 ) if( 0 )
{ {
printf("f = [ "); printf("f = [ ");
for(int i=0; i<FIR_SIZE; i++) for(int i=0; i<FIR_TAPS; i++) {
{ for(int j=0; j<FIR_PHASES; j++) {
printf("%.5f ", low_pass_fir[i]); printf("%.5f ", low_pass_fir[j][i]);
//printf("%i %.5f \n", i,low_pass_fir[i]); }
} }
printf("]; \n"); printf("]; \n");
} }
@ -215,7 +217,7 @@ int fm_mpx_get_samples(float *mpx_buffer) {
} }
fir_index++; // fir_index will point to newest valid data soon fir_index++; // fir_index will point to newest valid data soon
if(fir_index >= FIR_SIZE) fir_index = 0; if(fir_index >= FIR_TAPS) fir_index = 0;
// Store the current sample(s) into the FIR filter's ring buffer // Store the current sample(s) into the FIR filter's ring buffer
fir_buffer_left[fir_index] = audio_buffer[audio_index]; fir_buffer_left[fir_index] = audio_buffer[audio_index];
if(channels > 1) { if(channels > 1) {
@ -232,23 +234,21 @@ int fm_mpx_get_samples(float *mpx_buffer) {
//int iphase=FIR_PHASES-1; // test override //int iphase=FIR_PHASES-1; // test override
//printf("%d %d \n",fir_index,iphase); // diagnostics //printf("%d %d \n",fir_index,iphase); // diagnostics
// Sanity checks // Sanity checks
if ( iphase < 0 ) {iphase=0; printf("low\n"); } if ( iphase < 0 ) {iphase=0; printf("low\n"); }// Seems to run faster with these checks in place
if ( iphase >= FIR_PHASES ) {iphase=FIR_PHASES-2; printf("high\n"); } if ( iphase >= FIR_PHASES ) {iphase=FIR_PHASES-2; printf("high\n"); }
int fir_start = (fir_index - FIR_TAPS);
if( fir_start < 0 ) fir_start+=FIR_SIZE;
if( channels > 1 ) if( channels > 1 )
{ {
for(int fi=0; fi<FIR_TAPS; fi++) // fi = Filter Index for(int fi=0; fi<FIR_TAPS; fi++) // fi = Filter Index
{ // use bit masking to implement circular buffer { // use bit masking to implement circular buffer
out_left +=low_pass_fir[ iphase + (FIR_PHASES*fi) ]*fir_buffer_left[(fir_index-fi)&(FIR_SIZE-1)]; out_left+= low_pass_fir[iphase][fi]* fir_buffer_left[(fir_index-fi)&(FIR_TAPS-1)];
out_right+=low_pass_fir[ iphase + (FIR_PHASES*fi) ]*fir_buffer_right[(fir_index-fi)&(FIR_SIZE-1)]; out_right+=low_pass_fir[iphase][fi]*fir_buffer_right[(fir_index-fi)&(FIR_TAPS-1)];
} }
} }
else else
{ {
for(int fi=0; fi<FIR_TAPS; fi++) // fi = Filter Index for(int fi=0; fi<FIR_TAPS; fi++) // fi = Filter Index
{ // use bit masking to implement circular buffer { // use bit masking to implement circular buffer
out_left+=low_pass_fir[ iphase + (FIR_PHASES*fi) ] * fir_buffer_left[(fir_index-fi)&(FIR_SIZE-1)]; out_left+=low_pass_fir[iphase][fi] * fir_buffer_left[(fir_index-fi)&(FIR_TAPS-1)];
} }
} }