Quote:I don't (yet) have a miniDSP, but I understand how their filters work.
It sounds to me as Don is referring to the fact that IIR (Infinite-Impulse-Response) filters have a non-linear phase response. In other words, different frequencies are delayed by different amounts of time. FIR (Finite-Impulse-Response) filters, on the other hand, can have a linear phase response: a constant delay for all frequencies. This constant delay, called "group delay", is equal to the time between each sample, multiplied by half the size of the filter. This means that, if you use the same size FIR filter for each channel, everything comes out at the same relative phase as it went in, although delayed by the group-delay.
The biquad filters used by the miniDSP are a specific form of IIR filter, and therefore they will suffer from unequal delays for different frequencies. But the phase-shift is small, and some say its of no consequence (I cannot speak to that issue - I just don't know). It can also be mitigated somewhat, and a Linkwitz–Riley crossover is an excellent example of how to repair the phase delay.
Note that the time-domain adjustments in Audyssey or the miniDSP might not be useful unless they can be made to effect the delay with the inverse relationship to frequency as the FIR filter's effect.
Edited by MarkHotchkiss - 2/4/13 at 1:11pm