BASS_BFX_BQF structure

Used with BASS_FXGetParameters and BASS_FXSetParameters to retrieve and set the parameters of a biquad filters effect.

typedef struct{
    int lFilter;  
    float fCenter;
    float fGain;
    float fBandwidth;
    float fQ;
    float fS;
    int lChannel;


lFilter BASS_BFX_BQF_xxx filter types
One of the following filter types:
  BASS_BFX_BQF_BANDPASS constant 0 dB peak gain
  BASS_BFX_BQF_BANDPASS_Q constant skirt gain, peak gain = Q
fCenter Cutoff (central) frequency in Hz [1Hz..<info.freq/2]
fGain Used only for PEAKINGEQ and Shelving filters in dB [-15dB...0...+15dB] (can be above/below these limits)
fBandwidth Bandwidth in octaves (fQ is not in use (fBandwidth has a priority over fQ))
(between -3 dB frequencies for BANDPASS and NOTCH or between midpoint
(fGgain/2) gain frequencies for PEAKINGEQ)
fQ The EE kinda definition (linear) (if fBandwidth is not in use) [0.1.............1]
fS A "shelf slope" parameter (linear) (used only with Shelving filters)
when fS = 1, the shelf slope is as steep as you can get it and remain monotonically
increasing or decreasing gain with frequency.
lChannel The affected channels using BASS_BFX_CHANxxx flags

BiQuad filters are second-order recursive linear filters.

A low-pass filter is a filter that passes low-frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the fCenter frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter when used in audio applications. A low-pass filter is the opposite of a high-pass filter, and a band-pass filter is a combination of a low-pass and a high-pass.

A high-pass filter is an LTI filter that passes high frequencies well but attenuates (i.e., reduces the amplitude of) frequencies lower than the fCenter frequency. The actual amount of attenuation for each frequency is a design parameter of the filter. It is sometimes called a low-cut filter; the terms bass-cut filter or rumble filter are also used in audio applications.

A band-pass filter is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range. An example of an analogue electronic band-pass filter is an RLC circuit (a resistor–inductor–capacitor circuit). These filters can also be created by combining a low-pass filter with a high-pass filter.

In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a specific range to very low levels. It is the opposite of a band-pass filter. A notch filter is a band-stop filter with a narrow stopband (high Q factor). Notch filters are used in live sound reproduction (Public Address systems, also known as PA systems) and in instrument amplifier (especially amplifiers or preamplifiers for acoustic instruments such as acoustic guitar, mandolin, bass instrument amplifier, etc.) to reduce or prevent feedback, while having little noticeable effect on the rest of the frequency spectrum. Other names include 'band limit filter', 'T-notch filter', 'band-elimination filter', and 'band-reject filter'.

An all-pass filter is a signal processing filter that passes all frequencies equally, but changes the phase relationship between various frequencies. It does this by varying its propagation delay with frequency. Generally, the filter is described by the frequency at which the phase shift crosses 90° (i.e., when the input and output signals go into quadrature — when there is a quarter wavelength of delay between them).

A peaking equalizer raises or lowers a range of frequencies around a central point in a bell shape. A peaking equalizer with controls to adjust the level (fGain), fBandwidth (fQ) and center frequency (Hz) is called a parametric equalizer.
Peaking Equalizer in BASS_FX can be achieved directly and efficiently by BASS_FX_BFX_PEAKEQ

A low-shelf filter passes all frequencies, but increasing or reducing frequencies below the fCenter frequency by specified amount.

A high-shelf filter passes all frequencies, but increasing or reducing frequencies above the fCenter frequency by specified amount.

See also