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FIR filter speedup, reduced memory usage

master
SaucySoliton 2017-01-11 03:43:37 +00:00
rodzic 41c6523fc6
commit 81570e4733
1 zmienionych plików z 22 dodań i 22 usunięć
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44
src/fm_mpx.c
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@ -36,13 +36,12 @@
#define FIR_PHASES (32)
#define FIR_SIZE (1024) // MUST be a power of 2 for the circular buffer
#define FIR_TAPS (FIR_SIZE/FIR_PHASES)
#define FIR_TAPS (32) // MUST be a power of 2 for the circular buffer
size_t length;
// 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};
@ -61,8 +60,8 @@ int audio_index = 0;
int audio_len = 0;
float audio_pos;
float fir_buffer_left[FIR_SIZE] = {0};
float fir_buffer_right[FIR_SIZE] = {0};
float fir_buffer_left[FIR_TAPS] = {0};
float fir_buffer_right[FIR_TAPS] = {0};
int fir_index = 0;
int channels;
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) );
double x=0,y=0;
for(int i=1; i<=FIR_SIZE; i++) { // match indexing of Matlab script
sincpos = i-((FIR_SIZE+1.0)/2.0); // offset by 0.5 so sincpos!=0 (causes NaN x/0 )
//printf("%d=%f ", i,sincpos);
for(int i=0; i<FIR_TAPS; i++) {
for(int j=0; j<FIR_PHASES; j++) {
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) ;
y=a0*firlowpass + a1*x + b1*y ; // Find the combined impulse response
@ -150,19 +151,20 @@ int fm_mpx_open(char *filename, size_t len) {
firpreemph=y; // y could be replaced by firpreemph but this
// matches the example in the reference material
window = (.54 - .46 * cos(2*PI * (i) / (double) FIR_SIZE )) ; // Hamming window
low_pass_fir[i-1] = firpreemph * window * gain ; // store with C indexing
}
window = (.54 - .46 * cos(2*PI * (i) / (double) FIR_TAPS*FIR_PHASES )) ; // Hamming window
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);
if( 0 )
{
printf("f = [ ");
for(int i=0; i<FIR_SIZE; i++)
{
printf("%.5f ", low_pass_fir[i]);
//printf("%i %.5f \n", i,low_pass_fir[i]);
for(int i=0; i<FIR_TAPS; i++) {
for(int j=0; j<FIR_PHASES; j++) {
printf("%.5f ", low_pass_fir[j][i]);
}
}
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
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
fir_buffer_left[fir_index] = audio_buffer[audio_index];
if(channels > 1) {
@ -232,23 +234,21 @@ int fm_mpx_get_samples(float *mpx_buffer) {
//int iphase=FIR_PHASES-1; // test override
//printf("%d %d \n",fir_index,iphase); // diagnostics
// 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"); }
int fir_start = (fir_index - FIR_TAPS);
if( fir_start < 0 ) fir_start+=FIR_SIZE;
if( channels > 1 )
{
for(int fi=0; fi<FIR_TAPS; fi++) // fi = Filter Index
{ // 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_right+=low_pass_fir[ iphase + (FIR_PHASES*fi) ]*fir_buffer_right[(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][fi]*fir_buffer_right[(fir_index-fi)&(FIR_TAPS-1)];
}
}
else
{
for(int fi=0; fi<FIR_TAPS; fi++) // fi = Filter Index
{ // 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)];
}
}