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What is "estimate IR delay" in REW?
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- čas přidán 6. 08. 2024
- Use estimate IR delay to the adjust the zero time reference to make the phase graph readable.
From the REW manual:
Using a timing reference allows REW to eliminate the variable propagation delays within the computer and interface so that separate measurements have the same absolute timing. A Timing offset can be set that will shift the response relative to the timing reference, allowing the time of flight delay to be removed if using a loopback connection, for example. The timing offset can be set manually or from the figure calculated using the Estimate IR Delay function.
And: For speakers the delay estimate is based on the location of the peak of the impulse response. Subwoofers have a broad peak and a delayed response due to their limited bandwidth so the delay is instead measured relative to the start of the impulse response. The start of the impulse response cannot be located as precisely as the peak, however, so delay values are less accurate for subwoofer measurements.
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I love to geek out about the physics of sound. This channel focuses on the growing opportunity for live sound engineers to improve their confidence and consistency through the understanding of the principles of sound system design and optimization. My goal is to make this channel upfront and honest about my success and failure, so you can learn from both.
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![How to phase align main+sub in Smaart® [GSwSST34.1]](http://i.ytimg.com/vi/5leb1k4LUA0/mqdefault.jpg)
*Thanks for the great video.*
Andre from Hamburg, Germany
This was helpful to me as I am trying to compare the phase traces for two bookshelf speakers. One is a coaxial design and the other is a traditional two driver speaker. I noticed that the estimated IR offset is nearly identical to the loop back timing reference value for the measurement. Why shouldn't we just use that value? FWIW, while my two phase traces are smoother now, I still can't really understand what they're showing me! The unwrapped phase plot for the traditional 2 driver design is flatter from 700 Hz to 24 kHz than the line for the coaxial speaker which is the opposite of what I was expecting. I'll conclude by saying that I enjoy all of your videos Nathan. Thank you for providing so much good content on all things audio for us.
Hey John, good to hear from you.
> Why shouldn't we just use that value?
You can use any value. The simplest would be to just leave it at zero. The main reason to adjust this value is to make the phase graph human readable. If we estimate sound velocity at ~1ft/ms, then there should be about 1ms of delay for every foot between your mic and speaker.
> I still can't really understand what they're showing me!
For our purposes, a single solo phase trace without anything to compare it to is pretty useless. Usually we are either comparing it to a manufacturer's specification or comparing it to another speaker response that we want to combine it with. If you're interested, I have a workshop on the phase graph coming up in a few days: www.sounddesignlive.com/intro-phase-graph/
> Thank you for providing so much good content on all things audio for us.
You're welcome! Any requests?
@@nathanlively Hi Nathan, I do have a "How To in REW" request for you. Over on the Audio Science Review forums they use REW a lot with gating or windowing, to obtain pseudo-anechoic speaker measurements indoors. I've read the help page on this feature in REW, but would love to see a how-to video on it that walks me through the steps. Cheers.
excellent, thank you
Glad it helped
thank you
thank you~^^
Welcome!
Hi Nathan, i want to ask a question: I measure independent each way, lows and highs, only 1 channel. ¿I must apply estimate delay in the measured highs and put the delay for next measurement (bass)? i can remove the xover in bass to measure well but later i have to put it ona and filters PEQ too and phase will move. i want to estimate delay between bass and fullrange. 0.5 ms physically.
with initial delay is easy to align with alignment tool the problem is to know if the delays are ok. thanks
Hey Raul, The estimate delay feature is primarily used to make the phase trace human readable. It's optional. You could do all of your measurements without if you like. But yes, if you want to compare the relationship between two things, the measurements need to use the same time delay.
Also, I do not recommend defeating the low pass filter on your sub. This may lead to inaccurate alignment decisions.
@rlopezrb i would say you can use this technique to "time align" your sub w/ the mains...
regarding the phase shifting, any kind of filter, be it crossover, EQ, etc influences the phase.
that being said, with subs in general time alignment and phase alignment are easier to do by watching for the greatest output. meaning when the bass is the loudest, things are aligned as best as possible.
in rew you can use either incremental measurements or use the RTA tab to monitor the fq response in real time by using periodic pink noise.
Does anyone else have trouble with REW retaining the Timing Offset value even after starting a new session? This caused me at least 20 minutes of "what the heck" when I was trying to time align some front fills to the mains at a gig. I kept getting a negative time, which wasn't possible given the relative positions of the speakers. I finally realized that there was an old value in the Timing Offset box and once I zero'd that out, everything proceeded normally. Is there a config setting to not retain this value?
Hey John, thanks for sharing this experience. From my perspective this is an important feature that shouldn't be changed in order to keep everything with the same time reference, but I'd recommend that you reach out to John (REW founder) and ask him. He's great!
Hi Nathan, i have an issue and no clear explanations.
I would like use the Merlijn Van Veen's absolute/relative method to do the aligment between my subs and Tops. I use for this method the REW software with a USB mik-1.
During the absolute step: the top is plugged on the left side and the sub on the right side. The timing reference is the left side (the top speaker).
I measure first the top and then use to "estimate IR delay" and correct the delay. Then I mesure the sub (timing reference Left side).
Now is the issue...... By using the REW alignement tool without sub IR estimation delay the delay i have to apply to the sub is -16,8 ms! With sub IR estimation delay and shift, the delay to apply on sub is only 5.03 ms which make more sense to me.
What is your opininon?
Hello from France.
Hi Guillaume! Can I assume your measurement mic is equidistant from both main and sub?
16.8ms is a lot, but is totally possible. When you measure main + sub combined, do you get summation through the crossover region?
Feel free to send me your measurments.
@@nathanlively Hi Nathan, yes tke Umik-1 mic was on the ground equidistant from the sub and main.
The measurements (Top+sub) was not unfortunatly not done to check the summation That's for sure a mistake.
I will send you the measurement file by email so you can have a look on it.
Thanks for your reply.
Is it fair to say this is a similar function to “delay locate” in smaart?
Yes, it’s the exact same… I prefer to use the rise not the peak though so I adjust smaart a touch manually after ‘find delay’
Gradient a bit high here, what does IR stand for, what is it and then finally why would you need to correct for the delay.
Hi Clive! en.wikipedia.org/wiki/Impulse_response
> why would you need to correct for the delay.
You don't. Only if you want to make the phase trace easier ot read.
How does REW compare to Smaart, Systune etc?
Different workflow: Smaart most commonly used for its continuous mode workflow where you do everything in real time. REW is known for its offline workflow.
I don't know what I'm doing wrong but my impulse response doesn't look anything like it should. What you have at 2:10 looks fairly normal like what I would see using ARTA but what I'm getting in REW is not an impulse response. I don't know what it is.
Hey mfk, can you upload your mdat file or an image?
@@nathanlively I figured it out, use "%" instead of "dBFs" in the upper left. REW looks to have some really nice features but a bit of a clunky user interface. Thanks, mk
Is there any REW instruction for Dummies? :D Thanks for your efforts Mr Lively.
From what I've seen, there are lots of REW video on YT. No?
@@nathanlively Yes there are. I have now checked many and more of yours. Great Work.