Impulse response to set delay?

[atledreier]

Hello!

I've been toying with the idea of using Impulse Response graphs to time-delay my speakers properly.
My pre/pro have analog 7.1 inputs, and I plan on using these to do each speaker in turn. I will use the closest speaker as 'reference' as that will then always be the first impulse to arrive, and run two-channel sweeps and look at the impulse response to set timing.

My problem is this: My 7.1 channel input is analog bypass, so my regular distance, bass management and other settings don't apply to that input. So any distance settings I use would have to be calculated based on the impulse response. Will this be accurate enough?

So I plan to do this:
Run a sweep with my reference speaker and one of the others. The impulse graph will show a 'doube peak'. The time difference between these peaks will be the difference in distance between the speakers. So I take the time difference in ms and add a foot for each ms. Then add the distance of the reference speaker. Will this be correct?
I then use the same reference speaker, and do the same for the next speaker.

The problem is that I can't check my corrections, as my input doesn't use the distance settings in my OSD. Any tips on how to do this?

REW should be able to output 5.1 or 7.1 to digital with selected channels. Now that'd be sweet!

[brucek]

look at the impulse response to set timing.

The Energy/Time display would be more suited for this task. Even so, it's quite difficult to use this method.

brucek

[atledreier]

brucek wrote:

The Energy/Time display would be more suited for this task. Even so, it's quite difficult to use this method.

How so? Accuracy?
In my experience, acoustic delay and physical delay can vary some, so I want to get the timing right. I know how good it sounds when it's correct. Maybe I should just borrow some receiver with autosetup and use that delay...

[brucek]

Well, REW uses relative time, so you do indeed need a reference as you've said already - (actually the next release of REW is rumoured to have a loopback on the other channel to solve that problem, so you might want to wait a bit).

I found it a bit difficult to identify peaks from reflections, and certainly when doing one of the most important distance setups that is between the sub and mains, it becomes very tough. The sub has an extremely broad peak due to its limited bandwidth, so it can be hard to see the individual peaks of the sub and main on a single plot.

My telling you won't convince you that it's tough - you'll have to try it once and you'll see what I mean.

brucek

[atledreier]

I think I have the sub/front delay nailed, as close as I need it anyway. I'm more concerned with front/rear integration, really. Although I think maybe I just figured out the 'manual' way of doing it. By ear, and not very scientific, but still...

Somehow create a sound file that plays in the LF and LR, mono, and adjust by ear until the noise comes from where I want center to be. Level matching first, then adjust delay until I nail it.
Rinse and repeat for the right side.

Now to find a program that will generate a 5.1 stream on a disc....

[brucek]

Although I think maybe I just figured out the 'manual' way of doing it. By ear, and not very scientific, but still...

What about feeding the REW mono signal to the AUX (left and right) input of your receiver, then put the receiver in stereo mode so the LF and RF speakers are in play, then leave the LF hooked up normally, but disconnect the RF speaker and replace it with the LR.

Now the Energy/Time graph in REW will show two speakers at the listening position. LF and LR. The distance betwen them is the difference in time to the listening postion - or something like that anyway....

brucek

[atledreier]

hm.... clever... I might just have to try that! Didn't think to change the hookup after the pre/pro out to the power-amp... Cool, thanks!