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Mode
Two different working mode is available:
1) “Magn+Phase”. When this option is selected the FIR filter will compensate both magnitude and
phase of the measured IR. For the magnitude response a target curve can be applied.
2) “Phase only”. In this mode the FIR filter works on the phase response only, leaving the IR
magnitude unchanged.
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Max Frequency
Before calculating the FIR, the first thing the user should do is to look the frequency response of the
IR, mainly to check the upper cut frequency. This is useful to set the maximum operating frequency
above which the FIR filter will be neuter leaving the original IR unchanged. Moreover, it should be
remarked that:
1) The frequency response at very high frequencies can strongly depend on microphone position,
since the most of audio transducers are very directive in this frequency range. So it is worth to try
different microphone positions moving it of few centimeters, and choosing the one which gives the
best result.
2) The frequency response at very high frequencies can be the real one or just what the microphone
captures. If you are using a shoddy microphone, results in the high frequency range can be not
affordable. This doesn't mean that a satisfactory FIR equalization can't be done on a slightly
reduced band: just choose a max frequency value and try listening the result.
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Precision
The precision parameter, ranging from 1 to 10, is a measure of how accurate the magnitude
correction should be, with respect to the target curve. In particular, if the IR shows a deep dips in
the frequency response, using high values of the precision parameter implies that the FIR filter will
totally compensate them, with corresponding peaks in the FIR frequency response, which can result
in undesired audible ringing effects (tonal components will become visible in the time domain FIR
plot). On the contrary, using low values of the precision parameter limits the FIR to accurately
compensate only little lacks of the original IR, and to be less accurate on severe dips. This
parameter should be tried empirically and results can be checked basing on plotted curves and
listening tests.
The following picture compare two magnitude plots, where the precision parameter is set to 10
(max accuracy) in the right side graph and to 1 (min accuracy) in the left side graph. Group delay
plots are not shown since the precision parameter doesn't affect the phase compensation accuracy.
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