2 * various filters for ACELP-based codecs
4 * Copyright (c) 2008 Vladimir Voroshilov
6 * This file is part of FFmpeg.
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23 #ifndef AVCODEC_ACELP_FILTERS_H
24 #define AVCODEC_ACELP_FILTERS_H
29 * low-pass Finite Impulse Response filter coefficients.
31 * Hamming windowed sinc filter with cutoff freq 3/40 of the sampling freq,
32 * the coefficients are scaled by 2^15.
33 * This array only contains the right half of the filter.
34 * This filter is likely identical to the one used in G.729, though this
35 * could not be determined from the original comments with certainity.
37 extern const int16_t ff_acelp_interp_filter[61];
40 * Generic FIR interpolation routine.
41 * @param out [out] buffer for interpolated data
42 * @param in input data
43 * @param filter_coeffs interpolation filter coefficients (0.15)
44 * @param precision sub sample factor, that is the precision of the position
45 * @param frac_pos fractional part of position [0..precision-1]
46 * @param filter_length filter length
47 * @param length length of output
49 * filter_coeffs contains coefficients of the right half of the symmetric
50 * interpolation filter. filter_coeffs[0] should the central (unpaired) coefficient.
51 * See ff_acelp_interp_filter for an example.
54 void ff_acelp_interpolate(int16_t* out, const int16_t* in,
55 const int16_t* filter_coeffs, int precision,
56 int frac_pos, int filter_length, int length);
59 * high-pass filtering and upscaling (4.2.5 of G.729).
60 * @param out [out] output buffer for filtered speech data
61 * @param hpf_f [in/out] past filtered data from previous (2 items long)
62 * frames (-0x20000000 <= (14.13) < 0x20000000)
63 * @param in speech data to process
64 * @param length input data size
66 * out[i] = 0.93980581 * in[i] - 1.8795834 * in[i-1] + 0.93980581 * in[i-2] +
67 * 1.9330735 * out[i-1] - 0.93589199 * out[i-2]
69 * The filter has a cut-off frequency of 1/80 of the sampling freq
71 * @note Two items before the top of the out buffer must contain two items from the
72 * tail of the previous subframe.
74 * @remark It is safe to pass the same array in in and out parameters.
76 * @remark AMR uses mostly the same filter (cut-off frequency 60Hz, same formula,
77 * but constants differs in 5th sign after comma). Fortunately in
78 * fixed-point all coefficients are the same as in G.729. Thus this
79 * routine can be used for the fixed-point AMR decoder, too.
81 void ff_acelp_high_pass_filter(int16_t* out, int hpf_f[2],
82 const int16_t* in, int length);
84 #endif /* AVCODEC_ACELP_FILTERS_H */