avir::CDSPFIREQ Class Reference

#include <avir.h>

Public Member Functions
void	buildFilter (const double *const BandGains, double *const Filter)
int	getFilterLatency () const
int	getFilterLength () const
void	init (const double SampleRate, const double aFilterLength, const int aBandCount, const double MinFreq, const double MaxFreq, const bool IsLogBands, const double WFAlpha)

Static Public Member Functions
static int	calcFilterLength (const double aFilterLength, int &Latency)

Detailed Description

FIR filter-based equalizer generator.

Class implements an object used to generate symmetric-odd FIR filters with the specified frequency response (aka paragraphic equalizer). The calculated filter is windowed by the Peaked Cosine window function.

In image processing, due to short length of filters being used (6-8 taps) the resulting frequency response of the filter is approximate and may be mathematically imperfect, but still adequate to the visual requirements.

On a side note, this equalizer generator can be successfully used for audio signal equalization as well: for example, it is used in almost the same form in Voxengo Marvel GEQ equalizer plug-in.

Filter generation is based on decomposition of frequency range into spectral bands, with each band represented by linear and ramp "kernels". When the filter is built, these kernels are combined together with different weights that approximate the required frequency response.

Member Function Documentation

void avir::CDSPFIREQ::buildFilter	(	const double *const	BandGains,
		double *const	Filter
	)

Function creates symmetric-odd FIR filter with the specified gain levels at band crossover points.

Parameters

	BandGains	Array of linear gain levels, count=BandCount specified in the init() function.
[out]	Filter	Output filter buffer, length = getFilterLength().

static int avir::CDSPFIREQ::calcFilterLength ( const double  aFilterLength, int &  Latency  )

static

Function calculates filter's length (in samples) and latency depending on the required non-truncated filter length.

Parameters

	aFilterLength	Required filter length in samples (non-truncated).
[out]	Latency	Resulting latency (group delay) of the filter, in samples (taps).

Returns

Filter length in samples (taps).

int avir::CDSPFIREQ::getFilterLatency

(

)

const

Returns

Filter's latency (group delay), in samples (taps).

int avir::CDSPFIREQ::getFilterLength

(

)

const

Returns

Filter's length, in samples (taps).

void avir::CDSPFIREQ::init	(	const double	SampleRate,
		const double	aFilterLength,
		const int	aBandCount,
		const double	MinFreq,
		const double	MaxFreq,
		const bool	IsLogBands,
		const double	WFAlpha
	)

Function initializes *this object with the required parameters. The gain of frequencies beyond the MinFreq..MaxFreq range are controlled by the first and the last band's gain.

Parameters

SampleRate	Processing sample rate (use 2 for image processing).
aFilterLength	Required filter length in samples (taps). The actual filter length is truncated to an integer value.
aBandCount	Number of band crossover points required to control, including bands at MinFreq and MaxFreq.
MinFreq	Minimal frequency that should be controlled.
MaxFreq	Maximal frequency that should be controlled.
IsLogBands	"True" if the bands should be spaced logarithmically.
WFAlpha	Peaked Cosine window function's Alpha parameter.