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44 lines
2 KiB
C
44 lines
2 KiB
C
/* Configurable fixed point resampling SINC filter for mono and stereo audio.
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*
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* (C) 2022 irixxxx
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*
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* This work is licensed under the terms of any of these licenses
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* (at your option):
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* - GNU GPL, version 2 or later.
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* - MAME license.
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* See COPYING file in the top-level directory.
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*/
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struct resampler {
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int stereo; // mono or stereo?
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int taps; // taps to compute per output sample
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int interpolation; // upsampling factor (numerator)
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int decimation; // downsampling factor (denominator)
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int ratio_int; // floor(decimation/interpolation)
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u32 interp_inv; // Q16, 1.0/interpolation
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s16 *filter; // filter taps
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s32 *buffer; // filter history and input buffer (w/o zero stuffing)
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int buffer_sz; // buffer size in frames
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int buffer_idx; // buffer offset
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int phase; // filter phase for last output sample
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};
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typedef struct resampler resampler_t;
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/* Release a resampler */
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void resampler_free(resampler_t *r);
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/* Create a resampler with upsampling factor :interpolation and downsampling
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* factor :decimation, Kaiser windowed SINC polyphase FIR with bank size :taps.
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* The created filter has a size of :taps*:interpolation for upsampling and
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* :taps*:decimation for downsampling. :taps is limiting the cost per sample and
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* should be big enough to avoid inaccuracy (>= 8, higher is more accurate).
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* :cutoff is in [0..1] with 1 representing the Nyquist rate after decimation.
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* :beta is the Kaiser window beta.
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* :max_input is the maximum length in a resampler_update call */
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resampler_t *resampler_new(unsigned taps, unsigned interpolation, unsigned decimation,
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double cutoff, double beta, unsigned max_input, int stereo);
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/* Obtain :length resampled audio frames in :buffer. Use :get_samples to obtain
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* the needed amount of input samples */
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void resampler_update(resampler_t *r, s32 *buffer, int length,
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void (*generate_samples)(s32 *buffer, int length, int stereo));
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