filter.h File Reference

Digital filter. More...

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Typedefs
typedef struct _aubio_filter_t	aubio_filter_t
	Digital filter. More...

Functions
void	aubio_filter_do (aubio_filter_t *f, fvec_t *in)
	filter input vector (in-place) More...
void	aubio_filter_do_outplace (aubio_filter_t *f, const fvec_t *in, fvec_t *out)
	filter input vector (out-of-place) More...
void	aubio_filter_do_filtfilt (aubio_filter_t *f, fvec_t *in, fvec_t *tmp)
	filter input vector forward and backward More...
lvec_t *	aubio_filter_get_feedback (const aubio_filter_t *f)
	returns a pointer to feedback coefficients \( a_i \) More...
lvec_t *	aubio_filter_get_feedforward (const aubio_filter_t *f)
	returns a pointer to feedforward coefficients \( b_i \) More...
uint_t	aubio_filter_get_order (const aubio_filter_t *f)
	get order of the filter More...
uint_t	aubio_filter_get_samplerate (const aubio_filter_t *f)
	get sampling rate of the filter More...
uint_t	aubio_filter_set_samplerate (aubio_filter_t *f, uint_t samplerate)
	get sampling rate of the filter More...
void	aubio_filter_do_reset (aubio_filter_t *f)
	reset filter memory More...
aubio_filter_t *	new_aubio_filter (uint_t order)
	create new filter object More...
void	del_aubio_filter (aubio_filter_t *f)
	delete a filter object More...

Detailed Description

Digital filter.

This object stores a digital filter of order \(n\). It contains the following data:

• \( n*1 b_i \) feedforward coefficients
• \( n*1 a_i \) feedback coefficients
• \( n*c x_i \) input signal
• \( n*c y_i \) output signal

For convenience, the samplerate of the input signal is also stored in the object.

Feedforward and feedback parameters can be modified using aubio_filter_get_feedback() and aubio_filter_get_feedforward().

The function aubio_filter_do_outplace() computes the following output signal \( y[n] \) from the input signal \( x[n] \):

\begin{eqnarray*} y[n] = b_0 x[n] & + & b_1 x[n-1] + b_2 x[n-2] + ... + b_P x[n-P] \\ & - & a_1 y[n-1] - a_2 y[n-2] - ... - a_P y[n-P] \\ \end{eqnarray*}

The function aubio_filter_do() executes the same computation but modifies directly the input signal (in-place).

The function aubio_filter_do_filtfilt() version runs the filter twice, first forward then backward, to compensate with the phase shifting of the forward operation.

Some convenience functions are provided:

• new_aubio_filter_a_weighting() and aubio_filter_set_a_weighting(),
• new_aubio_filter_c_weighting() and aubio_filter_set_c_weighting().
• new_aubio_filter_biquad() and aubio_filter_set_biquad().

Definition in file filter.h.

Typedef Documentation

aubio_filter_t

typedef struct _aubio_filter_t aubio_filter_t

Digital filter.

Definition at line 72 of file filter.h.

Function Documentation

aubio_filter_do()

void aubio_filter_do	(	aubio_filter_t *	f,
		fvec_t *	in
	)

filter input vector (in-place)

Parameters

f	filter object as returned by new_aubio_filter()
in	input vector to filter

Examples:

temporal/test-biquad.c, and temporal/test-filter.c.

aubio_filter_do_filtfilt()

void aubio_filter_do_filtfilt	(	aubio_filter_t *	f,
		fvec_t *	in,
		fvec_t *	tmp
	)

filter input vector forward and backward

Parameters

f	aubio_filter_t object as returned by new_aubio_filter()
in	fvec_t input vector to filter
tmp	memory space to use for computation

Examples:

temporal/test-biquad.c, and temporal/test-filter.c.

aubio_filter_do_outplace()

void aubio_filter_do_outplace	(	aubio_filter_t *	f,
		const fvec_t *	in,
		fvec_t *	out
	)

filter input vector (out-of-place)

Parameters

f	filter object as returned by new_aubio_filter()
in	input vector to filter
out	output vector to store filtered input

Examples:

temporal/test-biquad.c, and temporal/test-filter.c.

aubio_filter_do_reset()

void aubio_filter_do_reset

(

aubio_filter_t *

f

)

reset filter memory

Parameters

f	filter object as returned by new_aubio_filter()

aubio_filter_get_feedback()

lvec_t* aubio_filter_get_feedback

(

const aubio_filter_t *

f

)

returns a pointer to feedback coefficients \( a_i \)

Parameters

f	filter object to get parameters from

Returns

a pointer to the \( a_0 ... a_i ... a_P \) coefficients

aubio_filter_get_feedforward()

lvec_t* aubio_filter_get_feedforward

(

const aubio_filter_t *

f

)

returns a pointer to feedforward coefficients \( b_i \)

Parameters

f	filter object to get coefficients from

Returns

a pointer to the \( b_0 ... b_i ... b_P \) coefficients

aubio_filter_get_order()

uint_t aubio_filter_get_order

(

const aubio_filter_t *

f

)

get order of the filter

Parameters

f	filter to get order from

Returns

the order of the filter

aubio_filter_get_samplerate()

uint_t aubio_filter_get_samplerate

(

const aubio_filter_t *

f

)

get sampling rate of the filter

Parameters

f	filter to get sampling rate from

Returns

the sampling rate of the filter, in Hz

Examples:

temporal/test-filter.c.

aubio_filter_set_samplerate()

uint_t aubio_filter_set_samplerate	(	aubio_filter_t *	f,
		uint_t	samplerate
	)

get sampling rate of the filter

Parameters

f	filter to get sampling rate from
samplerate	sample rate to set the filter to

Returns

the sampling rate of the filter, in Hz

del_aubio_filter()

void del_aubio_filter

(

aubio_filter_t *

f

)

delete a filter object

Parameters

f	filter object to delete

Examples:

temporal/test-a_weighting.c, temporal/test-biquad.c, temporal/test-c_weighting.c, and temporal/test-filter.c.

new_aubio_filter()

aubio_filter_t* new_aubio_filter

(

uint_t

order

)

create new filter object

This function creates a new aubio_filter_t object, given the order of the filter.

Parameters

order

order of the filter (number of coefficients)

Returns

the newly created filter object

Examples:

temporal/test-a_weighting.c, temporal/test-c_weighting.c, and temporal/test-filter.c.