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Thread: active crossover: fir vs iir

  1. #1
    Constant Bitrate
    Join Date
    Jan 2007

    active crossover: fir vs iir

    i'm going with an active setup using a carputer and vst software to do my crossover, and am currently planning on using a l/r vst plugin filter. it's my understanding that the disadvantage of iir filters is phase shift (90* every 6dB/oct of slope), and that fir filters have no such phase shift.

    but what if you just use a 24dB/oct (or a multiple thereof) slope? that's 360* of phase shift and thus no phase shift -- correct? even if i were to use a 12dB/oct or 36dB/oct slope (180* of phase shift), couldn't i just reverse the polarity of the mid and end up with the audio back in phase? is there anything wrong with my thinking on this? ..or is there some other benefit of a fir filter over an iir filter.



  2. #2
    Join Date
    Jan 2005
    The phase shift does not only occur at the xover point but occurs gradually throughout the affected freq range. But... you can invert the phase at 12, 36, 60, ... and get the drivers back in phase at the xover point. My experience is that at 12db per octave it makes an audible difference, at 36 it is much less audible, and at 60 it is inaudible (to me).

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