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FIR Filters offer the Halogen system designer additional flexibility that is not easily obtainable with the standard IIR filters offered in Halogen.
It is assumed that the FIR Filter will be designed by a means external to the Halogen software. The FIR filter block simply provides a mechanism to import the FIR filter coefficients, select the number of channels and display the result in a meaningful way once imported. The HAL DSP engine executes the imported filter.
The delay associated with the FIR block is obviously controlled by the coefficient design of the filter. Using a linear phase design will add delay equal to approximately half the number of FIR taps processed at our 48 kHz sampling rate. You may view this by selecting the group delay response graph in the FIR Filter properties dialog. In addition to the designed delay, the FIR block adds one sample of processing delay.
The file of FIR Taps to be imported should use one of the following formats:
Each Tap may be numerically formatted in one of three ways:
The file selected for importing may have either a .csv extension or a .txt extension. All FIR filter Taps are stored internally and in the DSP using a single precision IEEE floating point format.
note: The maximum number of Taps supported by the FIR filter block is 1024.
|Input nodes||Connection point for wiring inputs to the FIR filter block|
|Output nodes||Connection point for wiring the FIR filter outputs to other blocks|
|<Add> nodes||Click to add another Input/Output pair of nodes, or wire to the <Add> node to automatically create a new channel.|
(Hover over the thumbnail below to view the properties dialog box.)
|Graphical representation of the FIR filter that was last imported. Use View options to change graph content.|
Selecting Magnitude (selected by default) displays the FIR filter's Magnitude response on the graph.
Selecting Group Delay displays the filter's group delay on the graph.
Selecting Impulse displays the filter's impulse response on the graph.
|FIR Size (# taps imported)||Contains the number of taps of the FIR filter (as imported by the user). If you have not imported any Taps, the FIR Size box displays ---.|
|Import FIR Taps||Click this button to select and import an external file of FIR Taps. See Configuring the Block above for file format details.|
|Export FIR Taps||Click this button to export the current set of Taps to an external file. Exported Taps are saved in scientific notation (e.g. 1.154E-6)|
|Bypass||Check this box to bypass the FIR filter, which effectively turns the filter into a wire.|
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