Since a data block is what is passed on (as opposed to a data sample), the DSP has access to a few future samples within the block (represented as an array), allowing time-reversal operations required for zero-phase filtering (phase cancellation).Most algorithms that we use everyday like FFT etc. Digital data is mostly processed in finite-length blocks (packets), as opposed to processing one sample at a time.The time-reversed filtering works like this (look up "block-based processing" if interested in knowing more). Berchin has written above (if you already didn't).
Happy to find out if i'm doing something/ thinking something / incorrect.Ĭlick to expand.Mark, firstly I suggest that you read what Mr. I get measured results of the two processes in series, like I think would exist in real world global FIR correction. Or getting back to the electrical example I posted. However, when I apply a global FIR filter to a processing already in place, like an IIR DSP, or a passive or active analog speaker.
#Iir filter designer how to
I don't know how to do time reversed filtering.would like to learn yep.inside rePhase I can do the same thing.when the entire final output is one filter that rePhase does all the complex filter summation along KSTR's point, I think. I do get the idea of complex transfer multiplication though. i can kinda follow your math, but not so fully that I feel i understand it gut level. Thx for your willingness to look at what i've done. yep, always the chance i did something wrong. hope I'm not leading you and others on a goose chase.i don't think so, but we'll see.
#Iir filter designer series
Let me make a series of a few quick individual replies, and then I'll lay out in better detail what I did /am doing. Hi all, thank you for the replies, offers to help, and instructional comments. Unfortunately, what cancels mathematically won't necessarily cancel acoustically. The ringing will still occur, but the highpass ringing will cancel the lowpass ringing perfectly. Last bit of math: If a perfect-reconstruction crossover is implemented, then ringing in one band will be accompanied by identical ringing of opposite polarity in the other band. You can design a frequency response that has no ripples, in which case the impulse response will ring. You can design an impulse response that does not ring, in which case the frequency response will have ripples.
More math: A Gaussian-shaped, linear-phase frequency response also results in a Gaussian-shaped impulse response.Īny other shape will result in ringing in either the time domain or the frequency domain (as ripples in the response) or both. (It may also have its polarity inverted.) If you want to minimize the activity prior to the impulse response peak, then minimum-phase is the way to go - minimum phase concentrates the energy as close to the beginning of the impulse response as possible. In other words, the impulse response before the peak will always be the mirror image of the impulse response after the peak. There are some fundamental mathematics at work here, specifically: A linear-phase (and zero-phase is a form of linear phase) frequency response always results in a symmetric impulse response, and vice-versa. I'm not sure what I'm looking at in the various graphics above, but if pre-ring is what you are trying to eliminate, then linear phase is exactly the opposite of what you want to implement. There's more reasons to avoid global, but that's the easiest one to show some quick meas. Ok, i hope that makes a pretty good case against global FIR phase correction.
#Iir filter designer free
With an essentially a step response free of pre-ring. Ok, the same two Linkwitz-Riley 24dB/oct xovers at 200Hz and 1300Hz are summed together, but now are linear phase. (slight phase drift at 20kHz.not being picky here for this simple demo) Here is after global phase correction is applied, and is as expected. Here are two Linkwitz-Riley 24dB/oct IIR xovers at 200Hz and 1300Hz that are summed together to give mag and phase traces as shown, and are as expected. Out-right pre-ring is obvious in electrical IIR xovers summed together and then phase-linearized globally in a subsequent processing stage. Question came up in another thread.thought it best to reply in a new thread.Ī big reason that I think NOT to use global FIR on top an existing speaker setup, be it passive or active,
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