I'm just trying this out for fun to see if I like the results. I have a multichannel audio interface that is connected to a DAW (Ableton Live). For the channels outputting to my main L/R channels, I'm applying a FIR filter (that I manually generated using REW and rePhase) with LAConvolver. I'm also using a 3rd channel to send an unprocessed signal to my subwoofer. When I first tried this, the mains were delayed by quite a bit and I had to introduce delays to the L/R channels (~800 ms). I listened to a song that I knew well and played around with the time delay until it sounded right. It sounds surprisingly good but the OCD part of me wants to make sure the L/R and the subwoofer are perfectly time aligned. Does anyone know how I might be able to do this?
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Time aligning subwoofer after applying FIR to mains?
- Thread starter noobie1
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ernestcarl
Major Contributor
It may be necessary to use REW's alignment tool on individual channel measurements with a timing reference. Overlayed IR, step response, and phase graphs will also be very helpful in this endeavor. You can either individually apply FIRs to each section/channel prior alignment, or alternatively apply a "general" FIR filter to the summed response after alignment (post filter linearization). I prefer the former, but have also used the latter as well esp. when linearizing active studio speakers with built-in regular minimum phase crossovers.
Depending on what you're trying to do, the process can be relatively simple to complex (e.g. splitting/allocating the DSP work separately, multiple measurements/spatial averaging as opposed to a straightforward single-point method).
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- Thread Starter
- #3
@ernestcarl Thank you for the detailed response. Am I understanding the workflow correctly?
1) Take measurements for all 3 channels with a timing reference; L/R mains will have FIR filter active during the measurements while the subwoofer channel is unprocessed (i.e., no FIR).
2) Overlay the measurements and make sure the 3 channels are time aligned.
3) Create a new filter for the subwoofer channel which will introduce the appropriate time delay.
TIA
1) Take measurements for all 3 channels with a timing reference; L/R mains will have FIR filter active during the measurements while the subwoofer channel is unprocessed (i.e., no FIR).
2) Overlay the measurements and make sure the 3 channels are time aligned.
3) Create a new filter for the subwoofer channel which will introduce the appropriate time delay.
TIA
ernestcarl
Major Contributor
Well, you can go about it that way, too. But verify afterwards.
*Oops! Turns out I mixed up the min phase filter selections I used in the rePhase image example for the subwoofer a little bit as I got confused with it and my filters for the dedicated LFE channel -- due also to JRiver's labeling where the "sub" is the LFE. My 7.1c desk setup is really a bit more complicated as I split the EQ between the convolver and JRiver wherein the sub bass managed channels (LPF BW 8) diverges from the dedicated LFE channel (LPF BW 4 and 200Hz APF is applied to the latter as well to maintain phase coherence when the separate signals are altogether electrically/digitally summed).
**convolving the SUB no EQ measurement with the rePhase filter in the attachment (AxB via trace arithmetic function) and applying a delay offset of ~1ms should essentially give out the same actual measured subwoofer equalized response example in my previous post.
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dc655321
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Perhaps you already know this but, if your FIR filter is linear phase, the delay is trivially obtained without measurement.
- Thread Starter
- #6
I did not but it worked like a charm. Thanks!
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