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<blockquote data-quote="Mark Wilkinson" data-source="post: 147973" data-attributes="member: 8989">Re: FIR filtersOK guys, please don&#039;t shoot me for dumbing things down....you have a wonderful discussion going....But thinking about aligning subs to mains and and FIR latency..... it seems that FIR latency has to be at least equal to the group delay of the subs at LP crossover frequency as per IIR........???When we phase align subs to mains, I keep getting that means using a group delay implicit within the phase alignment freq range.&nbsp; Correct?&nbsp; (BTW, on an impulse response the group delay timing looks to me to be found on the second peak, not on the first peak where all the energy and no phase lag exists, yes?)&nbsp; (And is there a hotkey way to toggle between phase and group delay in Smaart?Anyway, in case I&#039;m barking anywhere near the right tree........say I&#039;ve got a sub high passed at 30hz 4th order, and LP&#039;ed at 100hz 4th order... the filters alone give a group delay of about 7ms at 100hz, and 20ms or so at 40hz....plus there&#039;s the inherent increasing delay of the driver as it goes lower... could easily end up with 30 or more ms delay at lowest freq.Seems like FIR has to account for this group delay however low we choose to try to flatten phase.So if we want to flatten phase much below sub LP, doesn&#039;t latency become unacceptable for almost any app except maybe pure playback?Do we just ignore this increasing sub lag below x-over?&nbsp; Whether IIR or FIR?If we could live with the latency to get phase flat to 20-30 hz, how many dang taps would it take?&nbsp; THX</blockquote>

[QUOTE="Mark Wilkinson, post: 147973, member: 8989"] Re: FIR filters OK guys, please don't shoot me for dumbing things down....you have a wonderful discussion going.... But thinking about aligning subs to mains and and FIR latency..... it seems that FIR latency has to be at least equal to the group delay of the subs at LP crossover frequency as per IIR........??? When we phase align subs to mains, I keep getting that means using a group delay implicit within the phase alignment freq range. Correct? (BTW, on an impulse response the group delay timing looks to me to be found on the [I]second[/I] peak, not on the first peak where all the energy and no phase lag exists, yes?) (And is there a hotkey way to toggle between phase and group delay in Smaart? Anyway, in case I'm barking anywhere near the right tree........say I've got a sub high passed at 30hz 4th order, and LP'ed at 100hz 4th order... the filters alone give a group delay of about 7ms at 100hz, and 20ms or so at 40hz....plus there's the inherent increasing delay of the driver as it goes lower... could easily end up with 30 or more ms delay at lowest freq. Seems like FIR has to account for this group delay however low we choose to try to flatten phase. So if we want to flatten phase much below sub LP, doesn't latency become unacceptable for almost any app except maybe pure playback? Do we just ignore this increasing sub lag below x-over? Whether IIR or FIR? If we could live with the latency to get phase flat to 20-30 hz, how many dang taps would it take? THX [/QUOTE]

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