The FIR Filter audio object implements a mechanism for time domain FIR filtering. FIR filters are more stable than IIR filters and can be designed to have linear phase response. However, they require a filter of higher order for similar response as an IIR and hence computationally intensive.
The filter operational mode can be controlled from GTT. The FIR filter coefficients can be provided through GTT custom panel from pre-stored coefficient files in .csv format.
Use Case: FIR filters are mostly used in applications that require linear phase. They are inherently more stable than IIR filters. However, FIR filters are generally computationally intensive. The applications include:
- Correction of frequency response errors in a loudspeaker.
- Phase correction in communication lines.
- Parametric and crossover filters implemented with FIRs can be implemented with or without phase shift.
FIR Filter Properties
Below table describes about the FIR Filter audio object properties and functionality.
| Properties | Description |
| # of Channels | The FIR Filter audio object has a number of input channels that is double the number of output audio channels.
|
| Number of taps for filter | Specify the number of elements which is the order of filter.
|
| Display Name | Display the name of the FIR Filter audio object in signal flow design. It can be changed based on the intended usage of the object. |
Mode
| Mode | Description |
| Normal | The FIR Audio Object shall perform the normal filter operation individually for each channel with the set of coefficients provided for each channel. The filter type can vary for each channel but the number of coefficients of all channels need to be the same. |
| Bypass | The FIR Audio Object shall copy the input signal to the output buffer bypassing the filter operations. Each channel can be selectively bypassed. |
| Off | The FIR Audio Object clears the output buffers. |
Additional Parameters
There are no additional parameters available for FIR Filter audio object.
Tuning Parameters
There are two sets of tunable parameters – mode and coefficients.
- Mode is a single variable.
- The number of coefficients depends on the tap-length value configured in GTT.
Let Nc denote the number of coefficients (taps), Ni number of channels. All filter coefficients are stored using floating point format. The filter coefficients are denoted by hi[k] where “i” is the filter’s index ranging from 0 to Ni−1 and “k” is the coefficient index (k = 0…Nc−1).
The generalized offset information of the two tunable parameters can be found below table.
FIR Tunable Parameters Offset
| Name | Description | Offset | Type | Unit | Range |
| mode[i] | Mode for filter i | UInt32 | – |
|
|
| Coefficient k for filter i | float | – | -1.0f; +1.0f |
FIR Tuneable Parameters Default Values
| Name | Description | Default Values |
| Mode | Operational Mode | 0 – Normal |
| FIR Coefficients | FIR Coefficient Array input | [1.0f, 0.0f, 0.0f, ……… 0.0f] – All pass |
Control Interface
There are no control parameters available for FIR Filter audio object.