AudioScience HPI Version_4.18.

The parametric equalizer control consists of a series of filters that are applied successively to the signal. More...
Enumerations  
enum  HPI_FILTER_TYPE { HPI_FILTER_TYPE_BYPASS = 0, HPI_FILTER_TYPE_LOWSHELF = 1, HPI_FILTER_TYPE_HIGHSHELF = 2, HPI_FILTER_TYPE_EQ_BAND = 3, HPI_FILTER_TYPE_LOWPASS = 4, HPI_FILTER_TYPE_HIGHPASS = 5, HPI_FILTER_TYPE_BANDPASS = 6, HPI_FILTER_TYPE_BANDSTOP = 7 } 
Equalizer filter types. More...  
Functions  
hpi_err_t  HPI_ParametricEQ_GetInfo (const hpi_hsubsys_t *phSubSys, hpi_handle_t hControl, uint16_t *pwNumberOfBands, uint16_t *pwOnOff) 
Find out the number of available bands of a parametric equalizer, and whether it is enabled or not.  
hpi_err_t  HPI_ParametricEQ_SetState (const hpi_hsubsys_t *phSubSys, hpi_handle_t hControl, uint16_t wOnOff) 
Turn a parametric equalizer on or off.  
hpi_err_t  HPI_ParametricEQ_GetBand (const hpi_hsubsys_t *phSubSys, hpi_handle_t hControl, uint16_t wIndex, uint16_t *pnType, uint32_t *pdwFrequencyHz, short *pnQ100, short *pnGain0_01dB) 
Get the settings of one of the filters in a parametric equalizer.  
hpi_err_t  HPI_ParametricEQ_SetBand (const hpi_hsubsys_t *phSubSys, hpi_handle_t hControl, uint16_t wIndex, uint16_t nType, uint32_t dwFrequencyHz, short nQ100, short nGain0_01dB) 
Set up one of the filters in a parametric equalizer.  
hpi_err_t  HPI_ParametricEQ_GetCoeffs (const hpi_hsubsys_t *phSubSys, hpi_handle_t hControl, uint16_t wIndex, short coeffs[5]) 
Retrieve the calculated IIR filter coefficients (scaled by 1000 into integers). 
The parametric equalizer control consists of a series of filters that are applied successively to the signal.
The number of filters available is obtained by calling HPI_ParametricEQ_GetInfo(), then the characteristics of each filter are configured using HPI_ParametricEQ_SetBand().
The equalizer as a whole can be turned on and off using HPI_ParametricEQ_SetState(). Filters can still be set up when the equalizer is switched off.
Equalizers are typically located on a LineIn input node or an OutStream node.
Obtain a control handle to an equalizer like this:
err = HPI_MixerGetControl( phSubSys, hMixer, HPI_SOURCENODE_LINEIN, 0, 0,0, // No destination node HPI_CONTROL_PARAMETRIC_EQ, &hControl );
enum HPI_FILTER_TYPE 
Equalizer filter types.
Used by HPI_ParametricEQ_SetBand()
hpi_err_t HPI_ParametricEQ_GetInfo  (  const hpi_hsubsys_t *  phSubSys, 
hpi_handle_t  hControl,  
uint16_t *  pwNumberOfBands,  
uint16_t *  pwOnOff  
) 
Find out the number of available bands of a parametric equalizer, and whether it is enabled or not.
phSubSys  Vestigial subsys handle (unused), may be set to NULL 
hControl  Equalizer control handle. 
pwNumberOfBands  Returned number of bands available. 
pwOnOff  Returned enabled status. 1 indicates enabled and 0 indicates disabled. 
hpi_err_t HPI_ParametricEQ_SetState  (  const hpi_hsubsys_t *  phSubSys, 
hpi_handle_t  hControl,  
uint16_t  wOnOff  
) 
Turn a parametric equalizer on or off.
phSubSys  Vestigial subsys handle (unused), may be set to NULL 
hControl  Equalizer control handle 
wOnOff  State setting, one of the HPI_SWITCH_STATES 
hpi_err_t HPI_ParametricEQ_GetBand  (  const hpi_hsubsys_t *  phSubSys, 
hpi_handle_t  hControl,  
uint16_t  wIndex,  
uint16_t *  pnType,  
uint32_t *  pdwFrequencyHz,  
short *  pnQ100,  
short *  pnGain0_01dB  
) 
Get the settings of one of the filters in a parametric equalizer.
See HPI_ParametricEQ_SetBand() for details of parameter interpretation.
phSubSys  Vestigial subsys handle (unused), may be set to NULL 
hControl  Equalizer control handle 
wIndex  Index of band to Get. 
pnType  Returned band type. 
pdwFrequencyHz  Returned band frequency. 
pnQ100  Returned filter Q * 100. 
pnGain0_01dB  Returned filter gain in 100ths of a dB. 
hpi_err_t HPI_ParametricEQ_SetBand  (  const hpi_hsubsys_t *  phSubSys, 
hpi_handle_t  hControl,  
uint16_t  wIndex,  
uint16_t  nType,  
uint32_t  dwFrequencyHz,  
short  nQ100,  
short  nGain0_01dB  
) 
Set up one of the filters in a parametric equalizer.
Set the parameters for one equalizer filter. The overall equalizer response will be a product of all its filter responses.
phSubSys  Vestigial subsys handle (unused), may be set to NULL 
hControl  Equalizer control handle. 
wIndex  Index of band to set. 
nType  The kind of filter that the band will implement has many different options. In the following descriptions, low and high frequencies mean relative to dwBandFrequency. "Elsewhere" means at frequencies different from dwBandFrequency, how different depends on Q (look at the following figures)

dwFrequencyHz  is the defining frequency of the filter. It is the center frequency of types HPI_FILTER_TYPE_ BANDPASS, HPI_FILTER_TYPE_BANDSTOP, HPI_FILTER_TYPE_EQ_BAND. It is the 3dB frequency of HPI_FILTER_TYPE_LOWPASS, HPI_FILTER_TYPE_HIGHPASS when Q=1 or resonant frequency when Q>1 and it is the half gain frequency of HPI_FILTER_TYPE_LOWSHELF, HPI_FILTER_TYPE_HIGHSHELF. The maximum allowable value is half the current adapter samplerate i.e. Fs/2. When the adapter samplerate is changed, the equalizer filters will be recalculated. If this results in the band frequency being greater than Fs/2, then the filter will be turned off. 
nQ100  controls filter sharpness. To allow the use of an integer parameter, Filter Q = dwQ100/100. In the following figure, gain is 20dB (10x) (nGain0_01dB=2000) and sampling frequency is normalized to 1Hz (10^0) and nFrequency is 0.1 x sampling frequency. Q=[0.2 0.5 1 2 4 8]. Q can also be thought of as affecting bandwidth or shelf slope of some of these filters. Bandwidth is measured in octaves (between 3 dB frequencies for BPF and notch or between midpoint (dBgain/2) gain frequencies for peaking EQ). The relationship between bandwidth and Q is: 1/Q = 2*sinh[ln(2)/2*bandwidth*omega/sin(omega)] (digital filter using BLT)
or 1/Q = 2*sinh[ln(2)/2*bandwidth]) (analog filter prototype)
Where omega = 2*pi*frequency/sampleRate
Shelf slope S, a "shelf slope" parameter (for shelving EQ only). When S = 1, the shelf slope is as steep as it can be and remain monotonically increasing or decreasing gain with frequency. The shelf slope, in dB/octave, remains proportional to S for all other values. 
nGain0_01dB  The gain is expressed in milliBels (100ths of a decibel). Allowable range is 1000 to +1000 mB. Usable range will likely be less than this. This parameter is only applicable to the equalizer filter types HPI_FILTER_TYPE_LOWSHELF,HPI_FILTER_TYPE_HIGHSHELF and HPI_FILTER_TYPE_EQ_BAND. Other filters always have unity gain in the passband. In the following figure, Q=1.0 and sampling frequency is normalized to 1Hz (10^0) and nFrequency is 0.1 x sampling frequency. dBgain=[20 10 0 10 20] For example, to produce the upper (red) curve in the "Filtertype_eq_band" graph: err= HPI_ParametricEQ_SetBand( phSubsys, hMicrophoneControl, HPI_FILTER_TYPE_EQ_BAND, 4410 // 4.41khz 100 // Q=1 20*100, // 20dB ); Effect of gain on EQ filters 
hpi_err_t HPI_ParametricEQ_GetCoeffs  (  const hpi_hsubsys_t *  phSubSys, 
hpi_handle_t  hControl,  
uint16_t  wIndex,  
short  coeffs[5]  
) 
Retrieve the calculated IIR filter coefficients (scaled by 1000 into integers).
phSubSys  Vestigial subsys handle (unused), may be set to NULL 
hControl  Equalizer control handle. 
wIndex  Index of band to Get. 
coeffs  Returned IIR filter coefficients * 1000 a1,a2,b0,b1,b2 (a0==0). 