diff options
| -rw-r--r-- | libavcodec/acelp_filters.c | 54 | ||||
| -rw-r--r-- | libavcodec/acelp_filters.h | 77 |
2 files changed, 131 insertions, 0 deletions
diff --git a/libavcodec/acelp_filters.c b/libavcodec/acelp_filters.c index 7e33a674f1..2aedbddab3 100644 --- a/libavcodec/acelp_filters.c +++ b/libavcodec/acelp_filters.c @@ -27,6 +27,60 @@ #define FRAC_BITS 13 #include "mathops.h" +const int16_t ff_acelp_interp_filter[61] = +{ /* (0.15) */ + 29443, 28346, 25207, 20449, 14701, 8693, + 3143, -1352, -4402, -5865, -5850, -4673, + -2783, -672, 1211, 2536, 3130, 2991, + 2259, 1170, 0, -1001, -1652, -1868, + -1666, -1147, -464, 218, 756, 1060, + 1099, 904, 550, 135, -245, -514, + -634, -602, -451, -231, 0, 191, + 308, 340, 296, 198, 78, -36, + -120, -163, -165, -132, -79, -19, + 34, 73, 91, 89, 70, 38, + 0, +}; + +void ff_acelp_interpolate( + int16_t* out, + const int16_t* in, + const int16_t* filter_coeffs, + int precision, + int pitch_delay_frac, + int filter_length, + int length) +{ + int n, i; + + assert(pitch_delay_frac >= 0 && pitch_delay_frac < precision); + + for(n=0; n<length; n++) + { + int idx = 0; + int v = 0x4000; + + for(i=0; i<filter_length;) + { + + /* The reference G.729 and AMR fixed point code performs clipping after + each of the two following accumulations. + Since clipping affects only the synthetic OVERFLOW test without + causing an int type overflow, it was moved outside the loop. */ + + /* R(x):=ac_v[-k+x] + v += R(n-i)*ff_acelp_interp_filter(t+6i) + v += R(n+i+1)*ff_acelp_interp_filter(6-t+6i) */ + + v += in[n + i] * filter_coeffs[idx + pitch_delay_frac]; + idx += precision; + i++; + v += in[n - i] * filter_coeffs[idx - pitch_delay_frac]; + } + out[n] = av_clip_int16(v >> 15); + } +} + void ff_acelp_convolve_circ( int16_t* fc_out, const int16_t* fc_in, diff --git a/libavcodec/acelp_filters.h b/libavcodec/acelp_filters.h index 9e497caec6..167faf72c3 100644 --- a/libavcodec/acelp_filters.h +++ b/libavcodec/acelp_filters.h @@ -26,6 +26,83 @@ #include <stdint.h> /** + * low-pass FIR (Finite Impulse Response) filter coefficients + * + * A similar filter is named b30 in G.729. + * + * G.729 specification says: + * b30 is based on Hamming windowed sinc functions, truncated at +/-29 and + * padded with zeros at +/-30 b30[30]=0. + * The filter has a cut-off frequency (-3 dB) at 3600 Hz in the oversampled + * domain. + * + * After some analysis, I found this approximation: + * + * PI * x + * Hamm(x,N) = 0.53836-0.46164*cos(--------) + * N-1 + * --- + * 2 + * + * PI * x + * Hamm'(x,k) = Hamm(x - k, 2*k+1) = 0.53836 + 0.46164*cos(--------) + * k + * + * sin(PI * x) + * Sinc(x) = ----------- (normalized sinc function) + * PI * x + * + * h(t,B) = 2 * B * Sinc(2 * B * t) (impulse response of sinc low-pass filter) + * + * b(k,B, n) = Hamm'(n, k) * h(n, B) + * + * + * 3600 + * B = ---- + * 8000 + * + * 3600 - cut-off frequency + * 8000 - sampling rate + * k - filter order + * + * ff_acelp_interp_filter[6*i+j] = b(10, 3600/8000, i+j/6) + * + * The filter assumes the following order of fractions (X - integer delay): + * + * 1/3 precision: X 1/3 2/3 X 1/3 2/3 X + * 1/6 precision: X 1/6 2/6 3/6 4/6 5/6 X 1/6 2/6 3/6 4/6 5/6 X + * + * The filter can be used for 1/3 precision, too, by + * passing 2*pitch_delay_frac as third parameter to the interpolation routine. + * + */ +extern const int16_t ff_acelp_interp_filter[61]; + +/** + * \brief Generic interpolation routine + * \param out [out] buffer for interpolated data + * \param in input data + * \param filter_coeffs interpolation filter coefficients (0.15) + * \param precision filter is able to interpolate with 1/precision precision of pitch delay + * \param pitch_delay_frac pitch delay, fractional part [0..precision-1] + * \param filter_length filter length + * \param length length of speech data to process + * + * filter_coeffs contains coefficients of the positive half of the symmetric + * interpolation filter. filter_coeffs[0] should the central (unpaired) coefficient. + * See ff_acelp_interp_filter fot example. + * + */ +void ff_acelp_interpolate( + int16_t* out, + const int16_t* in, + const int16_t* filter_coeffs, + int precision, + int pitch_delay_frac, + int filter_length, + int length); + +/** * \brief Circularly convolve fixed vector with a phase dispersion impulse * response filter (D.6.2 of G.729 and 6.1.5 of AMR). * \param fc_out vector with filter applied |