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-rw-r--r--apps/eq.c28
1 files changed, 22 insertions, 6 deletions
diff --git a/apps/eq.c b/apps/eq.c
index eecfc650d9..0a835d5484 100644
--- a/apps/eq.c
+++ b/apps/eq.c
@@ -217,12 +217,28 @@ void eq_hs_coefs(unsigned long cutoff, unsigned long Q, long db, long *c)
void eq_filter(long **x, struct eqfilter *f, unsigned num,
unsigned channels, unsigned shift)
{
- /* TODO: Implement generic filtering routine. */
- (void)x;
- (void)f;
- (void)num;
- (void)channels;
- (void)shift;
+ unsigned c, i;
+ long long acc;
+
+ /* Direct form 1 filtering code.
+ y[n] = b0*x[i] + b1*x[i - 1] + b2*x[i - 2] + a1*y[i - 1] + a2*y[i - 2],
+ where y[] is output and x[] is input.
+ */
+
+ for (c = 0; c < channels; c++) {
+ for (i = 0; i < num; i++) {
+ acc = (long long) x[c][i] * f->coefs[0];
+ acc += (long long) f->history[c][0] * f->coefs[1];
+ acc += (long long) f->history[c][1] * f->coefs[2];
+ acc += (long long) f->history[c][2] * f->coefs[3];
+ acc += (long long) f->history[c][3] * f->coefs[4];
+ f->history[c][1] = f->history[c][0];
+ f->history[c][0] = x[c][i];
+ f->history[c][3] = f->history[c][2];
+ x[c][i] = (acc << shift) >> 32;
+ f->history[c][2] = x[c][i];
+ }
+ }
}
#endif