diff options
| author | Andreas Eversberg <jolly@eversberg.eu> | 2016-05-01 10:17:21 +0200 |
|---|---|---|
| committer | Andreas Eversberg <jolly@eversberg.eu> | 2016-05-01 15:15:19 +0200 |
| commit | 28e7f1e9d1dc0e7574c3a8db9c56af38cbca2606 (patch) | |
| tree | d328c1cac3b1867ee7949991d32cdb93b03940c8 /src | |
| parent | 0c99848120f654538334491cc1abe450b831f3f0 (diff) | |
common code: Remove DC level before using Goertzel filter
A DC level degrades the quality of the filtered result
Diffstat (limited to 'src')
| -rw-r--r-- | src/common/goertzel.c | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/src/common/goertzel.c b/src/common/goertzel.c index 2410990..5a89165 100644 --- a/src/common/goertzel.c +++ b/src/common/goertzel.c @@ -32,17 +32,18 @@ /* return average value (rectified value), that can be 0..1 */ double audio_level(int16_t *samples, int length) { - int bias; + int32_t bias; double level; int sk; int n; - /* level calculation */ + /* calculate bias */ bias = 0; for (n = 0; n < length; n++) bias += samples[n]; bias = bias / length; + /* level calculation */ level = 0; for (n = 0; n < length; n++) { sk = samples[n] - bias; @@ -71,10 +72,17 @@ double audio_level(int16_t *samples, int length) */ void audio_goertzel(int16_t *samples, int length, int offset, int *coeff, double *result, int k) { + int32_t bias; int32_t sk, sk1, sk2; int64_t cos2pik; int i, n; + /* calculate bias to remove DC */ + bias = 0; + for (n = 0; n < length; n++) + bias += samples[n]; + bias = bias / length; + /* we do goertzel */ for (i = 0; i < k; i++) { sk = 0; @@ -83,7 +91,7 @@ void audio_goertzel(int16_t *samples, int length, int offset, int *coeff, double cos2pik = coeff[i]; /* note: after 'length' cycles, offset is restored to its initial value */ for (n = 0; n < length; n++) { - sk = ((cos2pik * sk1) >> 15) - sk2 + samples[offset++]; + sk = ((cos2pik * sk1) >> 15) - sk2 + samples[offset++] - bias; sk2 = sk1; sk1 = sk; if (offset == length) |