miniDSP Ltd, Hong Kong /
/ Features and specifications subject to change without prior notice
34
8.9
FIR
FILTERING
FIR ("finite impulse response") filtering allows construction of equalization filters with independent control of
amplitude and phase. The HA-DSP has an FIR filtering block on each channel as the last processing block prior to
the headphone output. There is an additional FIR filtering block on each cross-feed channel.
The parameters of each FI
R filter are viewed by clicking on the appropriate block e.g. “Left FIR & Output”:
FIR filtering should be considered an advanced topic. However, it is not difficult to “translate” a frequency
response from the PEQ block into FIR form, and this is covered on page 36.
8.9.1
FIR filtering overview
FIR filtering differs from the IIR ("infinite impulse response") filters used in the PEQ 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 non-recursive, and is specified by a large array of numbers.
These numbers are conventionally referred to as "taps." The HA-DSP can compute a total of 7168 taps. These
taps can be distributed as you wish across the four FIR blocks, with the limitation that each block must have 6 or
more taps and can have no more than 4096 taps. The number of taps allocated to a processing block is set in its
lower right corner:
