Looking the chart above, we can immediately note that the IRxFIR (the yellow curve) is much closer to
the ideal Dirac delta than the measured IR (the red curve). This is the improvement added by the FIR
filter.
The slightly difference between the IRxFIR and the Dirac delta is due to the fact that the FIR filter is
not working on the whole frequency response, but it is limited to a frequency range from about
200Hz to a MaxFreq (10kHz in this example). The lower limit depends on the IR measurement
technique (as described in the “IR Measurement” section), and on the poor resolution of the FIR filter
at low frequencies. The upper limit (MaxFreq) is a user defined parameter that will be described
afterwards.
Moreover, the time domain graph shows the latency added by the FIR filter, that is defined as the
time distance between the peak of the IR and the peak of the IRxFIR curve.
The magnitude plot here below shows the flattening effect of the FIR filter in the yellow curve, as well
as the frequency range where the filter is acting.
The graph below shows the group delay flattening effect (see the yellow curve), that is the main
achievement of the FIR filter: a flat group delay means a linear phase of the sound system (the group
delay is the derivative of the phase with respect to the frequency).
