Help needed with the REW 'Measure' function

andyr

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I've come back to REW after about a 3 month absence and am stuck - as the 'Measure' function isn't giving me a FR graph, the way it used to. :-((

So I'm hoping someone can advise me where I've gone wrong.

Here is my 'Measure' window:


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'Check levels' has been done - and the answer back was "Level OK'.

Note that the sweep is set to a max of 1kHz only as, in my 4-way active system, I currently only have the sub amps and woofer amps switched on. (I am trying to get the delay between the L sub and the L woofer, so I can ensure I set the delay inside my miniDSP plug-in to the correct value.)

So then I clicked on 'Start'. Previously, after the timing reference 'cheep' and then the sweep ... the FR graph appeared on the screen.

This time, however, I hear the 'cheep' - but then it just hangs. After a few seconds, I see this:


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All I am able to do is press 'Cancel' - to end up with a blank screen??

Can anyone advise? My version of REW is 5.20 Beta 47.

Thanks,
Andy
 

John Mulcahy

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As the message shows, REW is waiting for the timing reference. It is a 5 kHz - 20 kHz sweep so needs to be sent to a speaker or driver capable of reproducing it. You have selected the reference output to be the same as the measurement output, both the L channel of the "default output". Since you say there is only a sub and a woofer on that output the timing signal will not be properly reproduced.

If you are measuring the sub and the woofer together rather than separately you don't need a timing reference, since you are just looking at the relative timing of content in a single measurement.

It is better to select the actual output being used rather than leave it as default, since the default may change when interfaces are connected or disconnected.
 

andyr

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As the message shows, REW is waiting for the timing reference. It is a 5 kHz - 20 kHz sweep so needs to be sent to a speaker or driver capable of reproducing it. You have selected the reference output to be the same as the measurement output, both the L channel of the "default output". Since you say there is only a sub and a woofer on that output the timing signal will not be properly reproduced.

If you are measuring the sub and the woofer together rather than separately you don't need a timing reference, since you are just looking at the relative timing of content in a single measurement.

It is better to select the actual output being used rather than leave it as default, since the default may change when interfaces are connected or disconnected.
Aah, thanks John.

I didn't realize the timing reference is a 5 kHz - 20 kHz sweep ... I thought it was a sweep whose frequency limits were set by this parameter setting:

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I can hear the sweep through the drivers whose amps I have switched on - so I guess that parameter setting is just for the sweep ... and not for the timing reference?

And are you saying that I should not select this:

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... but should select the Microphone option in the dropdown?

Finally, you said:

If you are measuring the sub and the woofer together rather than separately you don't need a timing reference, since you are just looking at the relative timing of content in a single measurement.
Do you mean (when measuring the sub and the woofer together) that I simply de-select the timing reference? What will then give me the delay between the sub and the woofer, relative to my mic (which is at the listening position)?


Thanks,
Andy
 

John Mulcahy

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And are you saying that I should not select this:

View attachment 35001


... but should select the Microphone option in the dropdown?
It would be unusual for an output to be called microphone. Select the device name shown in the output devices list in the Soundcard preferences rather than default device, the the output name shown in the list rather than default output. It doesn't matter greatly though, since you are getting signal where you want it.
Do you mean (when measuring the sub and the woofer together) that I simply de-select the timing reference? What will then give me the delay between the sub and the woofer, relative to my mic (which is at the listening position)?
A timing reference is used to compare timing between different measurements. If you are making a combined measurement of sub and woofer together you could look at the group delay plot or the peak energy trace on the wavelet spectrogram, but both will be difficult to interpret with a listening position measurement due to the room's contribution. For measuring drivers in a speaker would normally put the mic closer to the speaker (1m, say) and move the speaker into the middle of the room to keep it as far away from boundaries as possible.
 

andyr

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Thank you, John. :T

Switching off the timing reference ... produced a graph! :)

Can I impose on you again ... I'm trying to get a handle on the amount that my subs are delayed, relative to my woofers (the subs are further away from my ears) and I'm wondering which graph/setting will show this.

I assume it's the "Impulse" graph? This is shown below:


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I'm at a loss to understand what this is telling me, in terms of delay? (I was expecting a graph like the below:)


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The above is from a paper on the miniDSP site.

In your last post, you said look at the Group Delay plot - but this doesn't tell me anything, either:


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Sub/woofer XO is 24dB L-R, HP & LP @ 80Hz.

fyi, I am running REW V5.20 Beta 47.

Thanks,
Andy
 

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John Mulcahy

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The impulse response provides two Y axis options. dBFS and %. Use % as explained in that miniDSP text you pasted for a similar display format. You only have a single measurement though, so you aren't going to see two impulse responses, just one.

From the group delay plot I'd guess the sub is delayed about 9 or 10 ms relative to the woofer.

You spoke about a 4 way active system, but you are referring to the subs as if they are separate units. Are they part of the speakers or separate? If they are separate you could use the alignment tool, but you will need to step back from measurement and do some reading first to understand what the tool does.
 

andyr

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Thank you, John.

Yes, I saw that reference to "%" in the miniDSP text - but couldn't understand how to achieve it. :sad:

But I have just figured it out. So I now have % on the Y axis ... however the graph itself means nothing to me. :redgrin:

Yes, the subs are separately located to my Maggies - but the XO is set by the 10x10HD miniDSP unit which forms the heart of my system. Hence, I refer to my system as '4-way active'.

I will research the alignment tool you linked to.

Thanks again.

Andy
 
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