This object computes bi-quadratic filter coefficients and calculates the output of the input audio buffers processed through the filters that users specify.
From SFD, the user can select what type of filtering to carry out via the “Biquad Topology” field:
- Direct Form I
- Direct Form II
- Transposed Direct Form II
From SFD, the user can enable/disable the ramping for tuning via the “Tune Ramping On/Off” field:
This object operates in one of the three modes:
- Parameter Mode – This mode generates a set of filters per channel, so each channel has its own set of unique filters.
- Parameter One Mode – This mode generates a set of filter coefficients for all audio channels. The only difference between this mode and the Parameter mode is that this mode generates one set of coefficients for all channels as opposed to one set per channel.
- Parameter One Mode Set Control Frequency – This mode only uses one filter and applies the filter characteristics to all channels as does the Parameter One Mode above. It also exposes one control (accessible from the HU) variable to manipulate the cut-off frequency.
Implemented ramping strategy is based on first-order low-pass interpolation scheme. The ramping is enabled only for direct form II and transposed direct form II topologies.
In SFD, users can set the number of channels (the number of input and output channels is the same) as well as the number of filters. Users can also select the object corresponding to the required mode.
In the GTT, the object exposes several of its variables based on mode:
For each filter in each channel, the object exposes the following parameters for both tuning and state-tuning:
- Frequency (cut-off)
- Gain (in dB)
- Q-value
- Type of filter:
- Bypass
- All pass 1
- All pass 2
- High pass butterworth 1
- High pass varq 2
- Low pass butterworth 1
- Low pass varq 2
- High shelf 1
- High shelf 2
- Low shelf 1
- Low shelf 2
- Parametric 2
- Bandpass 2
- Bandstop 2
- Amplifier
- Reson
- Bypass (on/off)
Parameter One Mode – This is identical to the Parameter Mode, except, instead of presenting the variables for each filter per channel, this mode only presents a set of coefficients per filter, regardless of the number of
channels.
Parameter One Mode Set Control Frequency – This is identical to Parameter One Mode but it has only one filter.
The Biquad object does not expose any variables for control except for the Parameter One Mode Set Control Frequency, where it exposes the cut-off frequency of the filter. When this parameter is changed then ramping is applied.
In addition to the above parameters, ParameterBiquad also exposes Ramp time configuration (both in state and tuning memory). For each channel in parameter mode and in Parameter One & Parameter One Mode Set Control Frequency single Ramp Time is exposed irrespective of number of channels.