mirror of
https://github.com/mackron/miniaudio.git
synced 2026-04-22 00:06:59 +02:00
David Reid
96f747d3f3
Previously this would result in a glitch, however in the interest of avoiding as many sources of glitching as possible, changing the format and/or channel count of a biquad filter (and by extension, anything derived from it, such as low-pass filters) will now result in an error.
447 lines
13 KiB
C
447 lines
13 KiB
C
#ifndef ma_lpf_h
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#define ma_lpf_h
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/**************************************************************************************************************************************************************
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Biquad Filter
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=============
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Biquad filtering is achieved with the `ma_biquad` API. Example:
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```c
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ma_biquad_config config = ma_biquad_config_init(ma_format_f32, channels, a0, a1, a2, b0, b1, b2);
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ma_result result = ma_biquad_init(&config, &biquad);
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if (result != MA_SUCCESS) {
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// Error.
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}
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...
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ma_biquad_process_pcm_frames(&biquad, pFramesOut, pFramesIn, frameCount);
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```
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Biquad filtering is implemented using transposed direct form 2. The denominator coefficients are a0, a1 and a2, and the numerator coefficients are b0, b1 and
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b2. The a0 coefficient is required and coefficients must not be pre-normalized.
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Supported formats are ma_format_s16 and ma_format_f32. If you need to use a different format you need to convert it yourself beforehand. When using
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ma_format_s16 the biquad filter will use fixed point arithmetic. When using ma_format_f32, floating point arithmetic will be used.
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Input and output frames are always interleaved.
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Filtering can be applied in-place by passing in the same pointer for both the input and output buffers, like so:
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```c
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ma_biquad_process_pcm_frames(&biquad, pMyData, pMyData, frameCount);
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```
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If you need to change the values of the coefficients, but maintain the values in the registers you can do so with `ma_biquad_reinit()`. This is useful if you
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need to change the properties of the filter while keeping the values of registers valid to avoid glitching or whatnot. Do not use `ma_biquad_init()` for this
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as it will do a full initialization which involves clearing the registers to 0. Note that changing the format or channel count after initialization is invalid
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and will result in an error.
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**************************************************************************************************************************************************************/
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typedef union
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{
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float f32;
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ma_int32 s32;
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} ma_biquad_coefficient;
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typedef struct
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{
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ma_format format;
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ma_uint32 channels;
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double a0;
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double a1;
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double a2;
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double b0;
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double b1;
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double b2;
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} ma_biquad_config;
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ma_biquad_config ma_biquad_config_init(ma_format format, ma_uint32 channels, double a0, double a1, double a2, double b0, double b1, double b2);
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typedef struct
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{
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ma_format format;
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ma_uint32 channels;
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ma_biquad_coefficient a1;
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ma_biquad_coefficient a2;
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ma_biquad_coefficient b0;
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ma_biquad_coefficient b1;
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ma_biquad_coefficient b2;
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ma_biquad_coefficient r1[MA_MAX_CHANNELS];
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ma_biquad_coefficient r2[MA_MAX_CHANNELS];
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} ma_biquad;
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ma_result ma_biquad_init(const ma_biquad_config* pConfig, ma_biquad* pBQ);
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ma_result ma_biquad_reinit(const ma_biquad_config* pConfig, ma_biquad* pBQ);
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ma_result ma_biquad_process_pcm_frames(ma_biquad* pBQ, void* pFramesOut, const void* pFramesIn, ma_uint64 frameCount);
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ma_uint32 ma_biquad_get_latency(ma_biquad* pBQ);
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/**************************************************************************************************************************************************************
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Low-Pass Filter
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===============
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Low-pass filtering is achieved with the `ma_lpf` API. Example:
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```c
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ma_lpf_config config = ma_lpf_config_init(ma_format_f32, channels, sampleRate, cutoffFrequency);
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ma_result result = ma_lpf_init(&config, &lpf);
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if (result != MA_SUCCESS) {
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// Error.
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}
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...
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ma_lpf_process_pcm_frames(&lpf, pFramesOut, pFramesIn, frameCount);
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```
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Supported formats are ma_format_s16 and ma_format_f32. If you need to use a different format you need to convert it yourself beforehand. Input and output
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frames are always interleaved.
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Filtering can be applied in-place by passing in the same pointer for both the input and output buffers, like so:
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```c
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ma_lpf_process_pcm_frames(&lpf, pMyData, pMyData, frameCount);
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```
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The low-pass filter is implemented as a biquad filter. If you need increase the filter order, simply chain multiple low-pass filters together.
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```c
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for (iFilter = 0; iFilter < filterCount; iFilter += 1) {
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ma_lpf_process_pcm_frames(&lpf[iFilter], pMyData, pMyData, frameCount);
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}
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```
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If you need to change the configuration of the filter, but need to maintain the state of internal registers you can do so with `ma_lpf_reinit()`. This may be
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useful if you need to change the sample rate and/or cutoff frequency dynamically while maintaing smooth transitions. Note that changing the format or channel
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count after initialization is invalid and will result in an error.
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**************************************************************************************************************************************************************/
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typedef struct
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{
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ma_format format;
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ma_uint32 channels;
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ma_uint32 sampleRate;
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double cutoffFrequency;
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} ma_lpf_config;
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ma_lpf_config ma_lpf_config_init(ma_format format, ma_uint32 channels, ma_uint32 sampleRate, double cutoffFrequency);
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typedef struct
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{
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ma_biquad bq; /* The low-pass filter is implemented as a biquad filter. */
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} ma_lpf;
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ma_result ma_lpf_init(const ma_lpf_config* pConfig, ma_lpf* pLPF);
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ma_result ma_lpf_reinit(const ma_lpf_config* pConfig, ma_lpf* pLPF);
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ma_result ma_lpf_process_pcm_frames(ma_lpf* pLPF, void* pFramesOut, const void* pFramesIn, ma_uint64 frameCount);
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ma_uint32 ma_lpf_get_latency(ma_lpf* pLPF);
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#endif /* ma_lpf_h */
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#if defined(MINIAUDIO_IMPLEMENTATION)
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#ifndef MA_BIQUAD_FIXED_POINT_SHIFT
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#define MA_BIQUAD_FIXED_POINT_SHIFT 14
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#endif
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static ma_int32 ma_biquad_float_to_fp(double x)
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{
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return (ma_int32)(x * (1 << MA_BIQUAD_FIXED_POINT_SHIFT));
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}
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ma_biquad_config ma_biquad_config_init(ma_format format, ma_uint32 channels, double a0, double a1, double a2, double b0, double b1, double b2)
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{
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ma_biquad_config config;
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MA_ZERO_OBJECT(&config);
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config.format = format;
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config.channels = channels;
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config.a0 = a0;
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config.a1 = a1;
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config.a2 = a2;
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config.b0 = b0;
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config.b1 = b1;
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config.b2 = b2;
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return config;
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}
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ma_result ma_biquad_init(const ma_biquad_config* pConfig, ma_biquad* pBQ)
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{
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if (pBQ == NULL) {
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return MA_INVALID_ARGS;
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}
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MA_ZERO_OBJECT(pBQ);
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if (pConfig == NULL) {
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return MA_INVALID_ARGS;
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}
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return ma_biquad_reinit(pConfig, pBQ);
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}
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ma_result ma_biquad_reinit(const ma_biquad_config* pConfig, ma_biquad* pBQ)
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{
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if (pBQ == NULL || pConfig == NULL) {
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return MA_INVALID_ARGS;
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}
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if (pConfig->a0 == 0) {
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return MA_INVALID_ARGS; /* Division by zero. */
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}
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/* Only supporting f32 and s16. */
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if (pConfig->format != ma_format_f32 && pConfig->format != ma_format_s16) {
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return MA_INVALID_ARGS;
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}
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/* The format cannot be changed after initialization. */
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if (pBQ->format != pConfig->format) {
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return MA_INVALID_OPERATION;
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}
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/* The channel count cannot be changed after initialization. */
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if (pBQ->channels != pConfig->channels) {
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return MA_INVALID_OPERATION;
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}
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pBQ->format = pConfig->format;
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pBQ->channels = pConfig->channels;
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/* Normalize. */
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if (pConfig->format == ma_format_f32) {
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pBQ->a1.f32 = (float)(pConfig->a1 / pConfig->a0);
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pBQ->a2.f32 = (float)(pConfig->a2 / pConfig->a0);
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pBQ->b0.f32 = (float)(pConfig->b0 / pConfig->a0);
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pBQ->b1.f32 = (float)(pConfig->b1 / pConfig->a0);
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pBQ->b2.f32 = (float)(pConfig->b2 / pConfig->a0);
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} else {
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pBQ->a1.s32 = ma_biquad_float_to_fp(pConfig->a1 / pConfig->a0);
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pBQ->a2.s32 = ma_biquad_float_to_fp(pConfig->a2 / pConfig->a0);
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pBQ->b0.s32 = ma_biquad_float_to_fp(pConfig->b0 / pConfig->a0);
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pBQ->b1.s32 = ma_biquad_float_to_fp(pConfig->b1 / pConfig->a0);
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pBQ->b2.s32 = ma_biquad_float_to_fp(pConfig->b2 / pConfig->a0);
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}
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return MA_SUCCESS;
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}
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static MA_INLINE void ma_biquad_process_pcm_frame_f32__direct_form_2_transposed(ma_biquad* pBQ, float* pY, const float* pX)
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{
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ma_uint32 c;
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const float a1 = pBQ->a1.f32;
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const float a2 = pBQ->a2.f32;
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const float b0 = pBQ->b0.f32;
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const float b1 = pBQ->b1.f32;
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const float b2 = pBQ->b2.f32;
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for (c = 0; c < pBQ->channels; c += 1) {
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float r1 = pBQ->r1[c].f32;
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float r2 = pBQ->r2[c].f32;
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float x = pX[c];
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float y;
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y = b0*x + r1;
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r1 = b1*x - a1*y + r2;
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r2 = b2*x - a2*y;
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pY[c] = y;
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pBQ->r1[c].f32 = r1;
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pBQ->r2[c].f32 = r2;
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}
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}
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static MA_INLINE void ma_biquad_process_pcm_frame_s16__direct_form_2_transposed(ma_biquad* pBQ, ma_int16* pY, const ma_int16* pX)
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{
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ma_uint32 c;
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const ma_int32 a1 = pBQ->a1.s32;
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const ma_int32 a2 = pBQ->a2.s32;
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const ma_int32 b0 = pBQ->b0.s32;
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const ma_int32 b1 = pBQ->b1.s32;
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const ma_int32 b2 = pBQ->b2.s32;
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for (c = 0; c < pBQ->channels; c += 1) {
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ma_int32 r1 = pBQ->r1[c].s32;
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ma_int32 r2 = pBQ->r2[c].s32;
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ma_int32 x = pX[c];
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ma_int32 y;
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y = (b0*x + r1) >> MA_BIQUAD_FIXED_POINT_SHIFT;
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r1 = (b1*x - a1*y + r2);
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r2 = (b2*x - a2*y);
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pY[c] = (ma_int16)ma_clamp(y, -32768, 32767);
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pBQ->r1[c].s32 = r1;
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pBQ->r2[c].s32 = r2;
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}
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}
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ma_result ma_biquad_process_pcm_frames(ma_biquad* pBQ, void* pFramesOut, const void* pFramesIn, ma_uint64 frameCount)
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{
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ma_uint32 n;
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if (pBQ == NULL || pFramesOut == NULL || pFramesIn == NULL) {
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return MA_INVALID_ARGS;
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}
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/* Note that the logic below needs to support in-place filtering. That is, it must support the case where pFramesOut and pFramesIn are the same. */
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if (pBQ->format == ma_format_f32) {
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/* */ float* pY = ( float*)pFramesOut;
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const float* pX = (const float*)pFramesIn;
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for (n = 0; n < frameCount; n += 1) {
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ma_biquad_process_pcm_frame_f32__direct_form_2_transposed(pBQ, pY, pX);
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pY += pBQ->channels;
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pX += pBQ->channels;
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}
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} else if (pBQ->format == ma_format_s16) {
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/* */ ma_int16* pY = ( ma_int16*)pFramesOut;
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const ma_int16* pX = (const ma_int16*)pFramesIn;
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for (n = 0; n < frameCount; n += 1) {
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ma_biquad_process_pcm_frame_s16__direct_form_2_transposed(pBQ, pY, pX);
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pY += pBQ->channels;
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pX += pBQ->channels;
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}
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} else {
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MA_ASSERT(MA_FALSE);
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return MA_INVALID_ARGS; /* Format not supported. Should never hit this because it's checked in ma_biquad_init() and ma_biquad_reinit(). */
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}
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return MA_SUCCESS;
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}
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ma_uint32 ma_biquad_get_latency(ma_biquad* pBQ)
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{
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if (pBQ == NULL) {
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return 0;
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}
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return 2;
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}
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ma_lpf_config ma_lpf_config_init(ma_format format, ma_uint32 channels, ma_uint32 sampleRate, double cutoffFrequency)
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{
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ma_lpf_config config;
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MA_ZERO_OBJECT(&config);
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config.format = format;
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config.channels = channels;
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config.sampleRate = sampleRate;
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config.cutoffFrequency = cutoffFrequency;
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return config;
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}
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static MA_INLINE ma_biquad_config ma_lpf__get_biquad_config(const ma_lpf_config* pConfig)
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{
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ma_biquad_config bqConfig;
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double q;
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double w;
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double s;
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double c;
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double a;
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MA_ASSERT(pConfig != NULL);
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q = 1 / sqrt(2);
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w = 2 * MA_PI_D * pConfig->cutoffFrequency / pConfig->sampleRate;
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s = sin(w);
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c = cos(w);
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a = s / (2*q);
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bqConfig.a0 = (double)( 1 + a);
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bqConfig.a1 = (double)(-2 * c);
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bqConfig.a2 = (double)( 1 - a);
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bqConfig.b0 = (double)((1 - c) / 2);
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bqConfig.b1 = (double)( 1 - c);
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bqConfig.b2 = (double)((1 - c) / 2);
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bqConfig.format = pConfig->format;
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bqConfig.channels = pConfig->channels;
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return bqConfig;
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}
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ma_result ma_lpf_init(const ma_lpf_config* pConfig, ma_lpf* pLPF)
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{
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ma_result result;
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ma_biquad_config bqConfig;
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if (pLPF == NULL) {
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return MA_INVALID_ARGS;
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}
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MA_ZERO_OBJECT(pLPF);
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if (pConfig == NULL) {
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return MA_INVALID_ARGS;
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}
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bqConfig = ma_lpf__get_biquad_config(pConfig);
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result = ma_biquad_init(&bqConfig, &pLPF->bq);
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if (result != MA_SUCCESS) {
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return result;
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}
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return MA_SUCCESS;
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}
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ma_result ma_lpf_reinit(const ma_lpf_config* pConfig, ma_lpf* pLPF)
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{
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ma_result result;
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ma_biquad_config bqConfig;
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if (pLPF == NULL || pConfig == NULL) {
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return MA_INVALID_ARGS;
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}
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bqConfig = ma_lpf__get_biquad_config(pConfig);
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result = ma_biquad_reinit(&bqConfig, &pLPF->bq);
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if (result != MA_SUCCESS) {
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return result;
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}
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return MA_SUCCESS;
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}
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static MA_INLINE void ma_lpf_process_pcm_frame_s16(ma_lpf* pLPF, ma_int16* pFrameOut, const ma_int16* pFrameIn)
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{
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ma_biquad_process_pcm_frame_s16__direct_form_2_transposed(&pLPF->bq, pFrameOut, pFrameIn);
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}
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static MA_INLINE void ma_lpf_process_pcm_frame_f32(ma_lpf* pLPF, float* pFrameOut, const float* pFrameIn)
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{
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ma_biquad_process_pcm_frame_f32__direct_form_2_transposed(&pLPF->bq, pFrameOut, pFrameIn);
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}
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ma_result ma_lpf_process_pcm_frames(ma_lpf* pLPF, void* pFramesOut, const void* pFramesIn, ma_uint64 frameCount)
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{
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if (pLPF == NULL) {
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return MA_INVALID_ARGS;
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}
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return ma_biquad_process_pcm_frames(&pLPF->bq, pFramesOut, pFramesIn, frameCount);
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}
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ma_uint32 ma_lpf_get_latency(ma_lpf* pLPF)
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{
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if (pLPF == NULL) {
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return 0;
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}
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return ma_biquad_get_latency(&pLPF->bq);
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}
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#endif |