bw_mm1

First-order multimode filter.

It implements an approximation of the Laplace-domain transfer function

H(s) = coeff_x + (2 pi fc coeff_lp) / (s + 2 pi fc)

where fc is the cutoff frequency.

Examples

Here you can download one or more example VST3 plugins for Windows, macOS and Linux. Source code of the audio engine(s) is included in the archive(s).

VST® is a trademark of Steinberg Media Technologies GmbH, registered in Europe and other countries.

API

Module type: DSP

bw_mm1_coeffs

typedef struct bw_mm1_coeffs bw_mm1_coeffs;

Coefficients and related.

bw_mm1_state

typedef struct bw_mm1_state bw_mm1_state;

Internal state and related.

bw_mm1_init()

static inline void bw_mm1_init(
	bw_mm1_coeffs * BW_RESTRICT coeffs);

Initializes input parameter values in coeffs.

bw_mm1_set_sample_rate()

static inline void bw_mm1_set_sample_rate(
	bw_mm1_coeffs * BW_RESTRICT coeffs,
	float                       sample_rate);

Sets the sample_rate (Hz) value in coeffs.

bw_mm1_reset_coeffs()

static inline void bw_mm1_reset_coeffs(
	bw_mm1_coeffs * BW_RESTRICT coeffs);

Resets coefficients in coeffs to assume their target values.

bw_mm1_reset_state()

static inline float bw_mm1_reset_state(
	const bw_mm1_coeffs * BW_RESTRICT coeffs,
	bw_mm1_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_mm1_reset_state_multi()

static inline void bw_mm1_reset_state_multi(
	const bw_mm1_coeffs * BW_RESTRICT              coeffs,
	bw_mm1_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 BW_NULL.

bw_mm1_update_coeffs_ctrl()

static inline void bw_mm1_update_coeffs_ctrl(
	bw_mm1_coeffs * BW_RESTRICT coeffs);

Triggers control-rate update of coefficients in coeffs.

bw_mm1_update_coeffs_audio()

static inline void bw_mm1_update_coeffs_audio(
	bw_mm1_coeffs * BW_RESTRICT coeffs);

Triggers audio-rate update of coefficients in coeffs.

bw_mm1_process1()

static inline float bw_mm1_process1(
	const bw_mm1_coeffs * BW_RESTRICT coeffs,
	bw_mm1_state * BW_RESTRICT        state,
	float                             x);

Processes one input sample x using coeffs, while using and updating state. Returns the corresponding output sample.

bw_mm1_process()

static inline void bw_mm1_process(
	bw_mm1_coeffs * BW_RESTRICT coeffs,
	bw_mm1_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 and updating both coeffs and state (control and audio rate).

bw_mm1_process_multi()

static inline void bw_mm1_process_multi(
	bw_mm1_coeffs * BW_RESTRICT                    coeffs,
	bw_mm1_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 and updating both the common coeffs and each of the n_channels states (control and audio rate).

bw_mm1_set_cutoff()

static inline void bw_mm1_set_cutoff(
	bw_mm1_coeffs * BW_RESTRICT coeffs,
	float                       value);

Sets the cutoff frequency value (Hz) in coeffs.

Valid range: [1e-6f, 1e12f].

Default value: 1e3f.

bw_mm1_set_prewarp_at_cutoff()

static inline void bw_mm1_set_prewarp_at_cutoff(
	bw_mm1_coeffs * BW_RESTRICT coeffs,
	char                        value);

Sets whether bilinear transform prewarping frequency should match the cutoff frequency (non-0) or not (0).

Default value: non-0 (on).

bw_mm1_set_prewarp_freq()

static inline void bw_mm1_set_prewarp_freq(
	bw_mm1_coeffs * BW_RESTRICT coeffs,
	float                       value);

Sets the prewarping frequency value (Hz) in coeffs.

Only used when the prewarp_at_cutoff parameter is off.

Valid range: [1e-6f, 1e12f].

Default value: 1e3f.

bw_mm1_set_coeff_x()

static inline void bw_mm1_set_coeff_x(
	bw_mm1_coeffs * BW_RESTRICT coeffs,
	float                       value);

Sets the input mode coefficient value in coeffs.

value must be finite.

Default value: 1.f.

bw_mm1_set_coeff_lp()

static inline void bw_mm1_set_coeff_lp(
	bw_mm1_coeffs * BW_RESTRICT coeffs,
	float                       value);

Sets the lowpass mode coefficient value in coeffs.

value must be finite.

Default value: 0.f.

bw_mm1_coeffs_is_valid()

static inline char bw_mm1_coeffs_is_valid(
	const bw_mm1_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_mm1_coeffs.

bw_mm1_state_is_valid()

static inline char bw_mm1_state_is_valid(
	const bw_mm1_coeffs * BW_RESTRICT coeffs,
	const bw_mm1_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 BW_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_mm1_state.

C++ wrapper

Brickworks::MM1

template<size_t N_CHANNELS>
class MM1 {
public:
	MM1();

	void setSampleRate(
		float sampleRate);

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

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

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

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

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

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

	void setCutoff(
		float value);

	void setPrewarpAtCutoff(
		bool value);

	void setPrewarpFreq(
		float value);

	void setCoeffX(
		float value);

	void setCoeffLp(
		float value);
...
}

Changelog

• Version 1.2.0:
  • Added support for BW_INCLUDE_WITH_QUOTES, BW_NO_CXX, and BW_CXX_NO_EXTERN_C.
  • Added debugging checks from bw_mm1_process() to bw_mm1_process_multi().
  • Added debugging checks in bw_mm1_process_multi() to ensure that buffers used for both input and output appear at the same channel indices.
  • Clarified which transfer function the module implements in the module description.
• Version 1.1.0:
  • Fixed computation of initial state in bw_mm1_reset_state().
  • Now using BW_NULL and BW_CXX_NO_ARRAY.
• Version 1.0.0:
  • Added bw_mm1_reset_state_multi() and updated C++ API in this regard.
  • Now bw_mm1_reset_state() returns the initial output value.
  • Added overloaded C++ reset() functions taking arrays as arguments.
  • bw_mm1_process() and bw_mm1_process_multi() now use size_t to count samples and channels.
  • Added more const and BW_RESTRICT specifiers to input arguments and implementation.
  • Moved C++ code to C header.
  • Added overloaded C++ process() function taking C-style arrays as arguments.
  • Removed usage of reserved identifiers.
  • Clearly specified parameter validity ranges.
  • Added debugging code.
• Version 0.6.0:
  • Removed dependency on bw_config.
• Version 0.5.0:
  • Added bw_mm1_process_multi().
  • Added C++ wrapper.
• Version 0.4.0:
  • Added initial input value to bw_mm1_reset_state().
• Version 0.3.0:
  • First release.