miniDSP Ltd, Hong Kong /
/ Features and specifications subject to change without prior notice
39
7.3.1
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 numbers for each plugin are given in Table 1.
•
In the OpenDRC 2x2 plugin, each channel has a fixed number of taps (6144).
•
In the case of the miniSHARC 4x8 plugins, taps can be distributed across the eight output channels, with the
limitation that each output channel must have 6 or more taps and can have no more than 2048 taps. The
decision on how many taps to allocate to each channel up to you, and should be determined after working
with an FIR filter design program (see below). The number of taps is set in the lower right corner (click on the
text entry box and type the desired number of taps, then press
Tab
or
Return
):
7.3.2
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
7.3.3
Filter file format
The filter coefficient file loaded in
File Mode
uses
IEEE 754 single-precision binary floating-point format
. The
number of entries in the file must not exceed the allocated number of taps.
In Manual Mode, the coefficients must be plain text in this format:
b0 = 1,
b1 = -1,
b2 = 0.5,
b3 = -0.5,
b4 = 0.2,
b5 = 1,
7.3.4
Loading filter coefficients
In
File Mode
:
1.
Click
Browse
, navigate to the file containing the filter coefficients, and open it. A dialog will appear
confirming the number of coefficients loaded.
2.
Confirm that the response curve is as you expect.
3.
Press
Send to DSP
. This will write the coefficients into the DSP's memory.
4.
To clear the filter coefficients, click
Unload FIR
and then
Send to DSP
.
