bw_osc_filt

Post-filter to decolorate oscillator waveshapers when antialiasing is on.

This linear time-invariant filter can be added in series of oscillator waveshapers that use PolyBLEP antialiasing (i.e., bw_osc_saw, bw_osc_pulse, bw_osc_tri) to compensate for high-frequency attenuation.

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_osc_filt_state

typedef struct bw_osc_filt_state bw_osc_filt_state;

Internal state and related.

bw_osc_filt_reset()

static inline float bw_osc_filt_reset_state(
	bw_osc_filt_state * BW_RESTRICT state,
	float                           x_0);

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

Returns the corresponding initial output value.

bw_osc_filt_reset_state_multi()

static inline void bw_osc_filt_reset_state_multi(
	bw_osc_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 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_osc_filt_process1()

static inline float bw_osc_filt_process1(
	bw_osc_filt_state * BW_RESTRICT state,
	float                           x);

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

bw_osc_filt_process()

static inline void bw_osc_filt_process(
	bw_osc_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 and updating state.

bw_osc_filt_process_multi()

static inline void bw_osc_filt_process_multi(
	bw_osc_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 and updating each of the n_channels states.

bw_osc_filt_state_is_valid()

static inline char bw_osc_filt_state_is_valid(
	const bw_osc_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.

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

C++ wrapper

Brickworks::OscFilt

template<size_t N_CHANNELS = 1>
class OscFilt {
public:
	OscFilt();
	
	void reset(
		float               x0 = 0.f,
		float * BW_RESTRICT y0 = BW_NULL);

# 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 = BW_NULL);

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

Changelog

• Version 1.2.2:
  • Added default value for N_CHANNELS in C++ API.
• Version 1.2.1:
  • Now using BW_NULL in the C++ API and implementation.
• Version 1.2.0:
  • Added support for BW_INCLUDE_WITH_QUOTES, BW_NO_CXX, and BW_CXX_NO_EXTERN_C.
  • Added debugging checks in bw_osc_filt_process_multi() to ensure that buffers used for both input and output appear at the same channel indices.
• Version 1.1.0:
  • Now using BW_NULL and BW_CXX_NO_ARRAY.
• Version 1.0.0:
  • Added initial input value to bw_osc_filt_reset_state().
  • Added bw_osc_filt_reset_state_multi() and updated C++ API in this regard.
  • Now bw_osc_filt_reset_state() returns the initial output value.
  • Added overloaded C++ reset() functions taking arrays as arguments.
  • bw_osc_filt_process() and bw_osc_filt_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.
  • Changed implementation topology to use less memory.
  • Removed usage of reserved identifiers.
  • Added debugging code.
• Version 0.6.0:
  • Removed dependency on bw_config.
• Version 0.5.0:
  • Added bw_osc_filt_process_multi().
  • Added C++ wrapper.
• Version 0.2.0:
  • Refactored API.
• Version 0.1.0:
  • First release.