Brickworks > API documentation > bw_pink_filt

bw_pink_filt

Description

Pinking filter.

This is a linear time-invariant filter approximately attenuating 3 dB/oct from about 0.000046 × Nyquist frequency to about 0.9 × Nyquist frequency. It can be used to turn white noise into pink noise (hence the name).

The filter design is based on

P. P. La Pastina and S. D'Angelo, "Optimal Integer Order Approximation of Fractional Order Filters", Proc. 24th Intl. Conf. Digital Audio Effects (DAFx20in21), pp. 89-96, Vienna, Austria, September 2021.

Info

Module type: dsp

Version: 1.0.0

Requires:

API

bw_pink_filt_coeffs

typedef struct bw_pink_filt_coeffs bw_pink_filt_coeffs;

Coefficients and related.

bw_pink_filt_state

typedef struct bw_pink_filt_state bw_pink_filt_state;

Internal state and related.

bw_pink_filt_init()

static inline void bw_pink_filt_init(
	bw_pink_filt_coeffs * BW_RESTRICT coeffs);

Initializes input parameter values in coeffs.

bw_pink_filt_set_sample_rate()

static inline void bw_pink_filt_set_sample_rate(
	bw_pink_filt_coeffs * BW_RESTRICT coeffs,
	float                             sample_rate);

Sets the sample_rate (Hz) value in coeffs.

bw_pink_filt_reset_coeffs()

static inline void bw_pink_filt_reset_coeffs(
	bw_pink_filt_coeffs * BW_RESTRICT coeffs);

Resets coefficients in coeffs to assume their target values.

bw_pink_filt_reset_state()

static inline float bw_pink_filt_reset_state(
	const bw_pink_filt_coeffs * BW_RESTRICT coeffs,
	bw_pink_filt_state * BW_RESTRICT        state,
	float                                   x_0);

Resets the given state to its initial values using the given coeffs and the initial input value x_0.

Returns the corresponding initial output value.

bw_pink_filt_reset_state_multi()

static inline void bw_pink_filt_reset_state_multi(
	const bw_pink_filt_coeffs * BW_RESTRICT              coeffs,
	bw_pink_filt_state * BW_RESTRICT const * BW_RESTRICT state,
	const float *                                        x_0,
	float *                                              y_0,
	size_t                                               n_channels);

Resets each of the n_channels states to its initial values using the given coeffs and the corresponding initial input value in the x_0 array.

The corresponding initial output values are written into the y_0 array, if not NULL.

bw_pink_filt_update_coeffs_ctrl()

static inline void bw_pink_filt_update_coeffs_ctrl(
	bw_pink_filt_coeffs * BW_RESTRICT coeffs);

Triggers control-rate update of coefficients in coeffs.

bw_pink_filt_update_coeffs_audio()

static inline void bw_pink_filt_update_coeffs_audio(
	bw_pink_filt_coeffs * BW_RESTRICT coeffs);

Triggers audio-rate update of coefficients in coeffs.

bw_pink_filt_process1()

static inline float bw_pink_filt_process1(
	const bw_pink_filt_coeffs * BW_RESTRICT coeffs,
	bw_pink_filt_state * BW_RESTRICT        state,
	float                                   x);

static inline float bw_pink_filt_process1_scaling(
	const bw_pink_filt_coeffs * BW_RESTRICT coeffs,
	bw_pink_filt_state * BW_RESTRICT        state,
	float                                   x);

These function process one input sample x using coeffs, while using and updating state. They return the corresponding output sample.

In particular:

Whether sample rate scaling is enabled or not is unchecked even for debugging purposes.

bw_pink_filt_process()

static inline void bw_pink_filt_process(
	bw_pink_filt_coeffs * BW_RESTRICT coeffs,
	bw_pink_filt_state * BW_RESTRICT  state,
	const float *                     x,
	float *                           y,
	size_t                            n_samples);

Processes the first n_samples of the input buffer x and fills the first n_samples of the output buffer y, while using coeffs and both using and updating state.

bw_pink_filt_process_multi()

static inline void bw_pink_filt_process_multi(
	bw_pink_filt_coeffs * BW_RESTRICT                    coeffs,
	bw_pink_filt_state * BW_RESTRICT const * BW_RESTRICT state,
	const float * const *                                x,
	float * const *                                      y,
	size_t                                               n_channels,
	size_t                                               n_samples);

Processes the first n_samples of the n_channels input buffers x and fills the first n_samples of the n_channels output buffers y, while using the common coeffs and both using and updating each of the n_channels states.

bw_pink_filt_set_sample_rate_scaling()

static inline void bw_pink_filt_set_sample_rate_scaling(
	bw_pink_filt_coeffs * BW_RESTRICT coeffs,
	char                              value);

Sets whether the output should be scaled (value non-0) or not (0) according to the sample rate in coeffs.

In order to keep the magnitude response consistent at different sample rates, the output of this filter should be accordingly scaled. The 44100 Hz sample rate is used as a reference (that is, the scaling factor at that sample rate is 1.f).

Default value: 0 (off).

bw_pink_filt_get_scaling_k()

static inline float bw_pink_filt_get_scaling_k(
	const bw_pink_filt_coeffs * BW_RESTRICT coeffs);

Returns the sample rate scaling factor that is applied or would be applied if sample rate scaling were enabled, as stored in coeffs.

bw_pink_filt_coeffs_is_valid()

static inline char bw_pink_filt_coeffs_is_valid(
	const bw_pink_filt_coeffs * BW_RESTRICT coeffs);

Tries to determine whether coeffs is valid and returns non-0 if it seems to be the case and 0 if it is certainly not. False positives are possible, false negatives are not.

coeffs must at least point to a readable memory block of size greater than or equal to that of bw_pink_filt_coeffs.

bw_pink_filt_state_is_valid()

static inline char bw_pink_filt_state_is_valid(
	const bw_pink_filt_coeffs * BW_RESTRICT coeffs,
	const bw_pink_filt_state * BW_RESTRICT  state);

Tries to determine whether state is valid and returns non-0 if it seems to be the case and 0 if it is certainly not. False positives are possible, false negatives are not.

If coeffs is not NULL extra cross-checks might be performed (state is supposed to be associated to coeffs).

state must at least point to a readable memory block of size greater than or equal to that of bw_pink_filt_state.

C++ wrapper

Brickworks::PinkFilt
template<size_t N_CHANNELS>
class PinkFilt {
public:
	PinkFilt();

	void setSampleRate(
		float sampleRate);

	void reset(
		float               x0 = 0.f,
		float * BW_RESTRICT y0 = nullptr);

	void reset(
		float                                       x0,
		std::array<float, N_CHANNELS> * BW_RESTRICT y0);

	void reset(
		const float * x0,
		float *       y0 = nullptr);

	void reset(
		std::array<float, N_CHANNELS>               x0,
		std::array<float, N_CHANNELS> * BW_RESTRICT y0 = nullptr);

	void process(
		const float * const * x,
		float * const *       y,
		size_t                nSamples);

	void process(
		std::array<const float *, N_CHANNELS> x,
		std::array<float *, N_CHANNELS>       y,
		size_t                                nSamples);

	void setSampleRateScaling(
		bool value);

	float getScalingK();
...
}

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