mi niDSP Ltd, Hong Kong /
/ Features and speci fi cations subject to change wi thout pri or noti ce
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Browse
Opens a filter browser to select a file containing FIR filter coefficients. (See FIR filter file format
below).
Unload FIR
Deletes the currently loaded filter coefficients from the plugin (all coefficients are set to zero).
Bypass
Disables the FIR filter. The filter is disabled when the button is "lit."
Send to DSP
Writes the current set of filter coefficients into the DSP memory.
File Mode / Manual Mode
In File Mode, the window displays the Browse and Unload FIR buttons as shown above. In
Manual Mode, the display changes to allow direct text entry of the FIR filter coefficients, as
shown below. The coefficients can be pasted into the window from a text editor.
5.3.1
FIR filtering overview
FIR ("finite impulse response") filtering differs from the IIR ("infinite impulse response") filters used in the PEQ
and crossover blocks. Technically speaking, IIR filters are recursive, meaning that each output value is partially
calculated from earlier output values as well as from input values. An FIR filter is specified by a large array of
numbers, whereas an IIR filter requires only a fairly small of values to be specified.
These numbers are conventionally referred to as "taps." The tap allocation is asymmetric:
Output channel 1 has 2300 taps.
Output channel 2 has 300 taps.
This tap allocation is suited for typical two-way crossover applications. The longer filter on output channel 1
allows for woofer correction down to reasonably low frequencies (frequency resolution is about 21 Hz) while the
short filter on output channel 2 is suitable for typical crossover and driver correction for a tweeter.
Note that the delay on the woofer output channel will probably need to be set to allow for the different delays
created by the two filters.
5.3.2
FIR filter design software
The filter coefficients must be created with the aid of filter design software. miniDSP does not provide any such
software, instead referring you to the many software packages available for this purpose (both freeware and
commercial). Please see the
page on our website.
Be sure to set the filter design software to use a 48 kHz sample rate. If not set to 48 kHz, the filters
will not be correct.
