# Setting Loopback Timing Reference Correctly



## Twolions (May 21, 2014)

Hi all,

I'm currently stuck at trying to get my drivers time aligned using REW. I have setup the system in the following manner:

1.) ECM8000 is connected to Steinberg UR22 preamp/audio interface on the right intup channel.
2.) Steinberg is connected via USB to the Mac Mini. 
3.) Mac Mini is connected to the Unico CD Primo DAC via USB.
4.) I have a loopback cable going from left in to left out of the Steinberg UR22.
5.) I have the RIGHT channel selected in REW for making measurements.
6.) I don't have any connection going from Steinberg right out to my DAC or any other device in the chain.

For reference, the Unico CD Primo goes into a Conrad Johnson PV12, which then goes into Dynacord DSP600 and the stereo 3-way is then fed to the power amps/subs.

For some reason, when I take the impuls measurements in REW, make the changes as suggested in the overlay graph on my DSP600 and re-measure again in REW, the distance for the IRs remains the same, nothing changes when I increase the distance on any given output channel on my DSP600 by any amount of ms. 

What am I doing wrong here? 

Thanks in advance.


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## JohnM (Apr 11, 2006)

For the timing reference to be meaningful it needs to be following the same path as the measurement and just shortcut it at the soundcard output/input (or some later path that excludes the acoustic part). For your setup the UR22 left input would need to be connected to the left output of your DAC (and you need to tick the box in REW's Analysis preferences to use loopback as timing reference). Best would be to use the UR22 for output as well, that way you don't have the complication of running two different devices with unsynced clocks.


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## Twolions (May 21, 2014)

Hey John,

Thanks, yes, loopback is checked. Got it on having the left input of UR22 connected to the left DAC output. 

Can you please clarify real quickly how I'd use the UR22 as the output in my setup (from a connection standpoint)?

Thanks,
Uros


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## AudiocRaver (Jun 6, 2012)

Don''t know your experience level on the topic, but if you need more background, it has been discussed in detail in the following threads. We have a couple of resident experts who have documented their experiences and helped others. It is heavy reading, but if you can get through it, you will have had the equivalent of a university-level course.

Aligning Driver Phase

Understanding Phase Graphs

Filtered Impulse Response

Time Alignment


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## Twolions (May 21, 2014)

Thanks Wayne. Been using HolmsImpulse mostly for time alignment, new to REW in that regard. Anyway, yes, went through most of these threads. Almost there on a lot of these things but quite hard to digest everything. 

Thanks for your help, guys.


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## JohnM (Apr 11, 2006)

Twolions said:


> Can you please clarify real quickly how I'd use the UR22 as the output in my setup (from a connection standpoint)?


Connect the left or right channel of your system (depending on which you are measuring) to the UR22 right line output instead of to the Unico output.


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## Twolions (May 21, 2014)

Understood, excellent, this was very helpful. I'll follow up with measurements come weekend; maybe someone finds it useful. Thanks again for your help.


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## Twolions (May 21, 2014)

Hi guys,

So as per your advice (or how I've interpreted it) I have the left and right outputs of my UR22 feeding the left/right AUX IN on the preamp. Steinberg UR22 is being used for output.

To set the loopback however with correct timing am I right to assume that I would now have to connect ONE of my six channel outs on the DSP to the left IN of UR22? 

My problem right now is that I don't have a classic setup, meaning just a preamp going to the power amps and instead have the preamp going into the DSP with 6 outs (each feeding different amps/drivers).

So to make this short:

1.) Is it correct to set the loopback where I take ANY of the six channel outs on my DSP and connect it with UR22 left IN?

Would it perhaps be sufficient just to connect the preamp left out? I am assuming not.

Thanks.


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## jtalden (Mar 12, 2009)

Yes, for timing studies there needs to be a loopback cable on a loopback channel. 

The measurement channel can be changed without changing the loopback channel. So the outputs of the soundcard can be initially set to channel 1 for measurement and channel 6 for loopback.

The measurement channel can then be changed to channel 2, 3, etc., while still using channel 6 for loopback timing.

The loopback timing channel cannot bypass the DAC. The timing would be lost that way. So the cable would connect output 6 of the DAC to the input 1 of the UR22. Of course output 1 (or 2) of the UR22 needs to be passing though to the DAC 6 output for all measurements.


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## Twolions (May 21, 2014)

J thanks for the clarification and confirmation. I think I'm almost set


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## Twolions (May 21, 2014)

Hey J,

So, quickly, what I'm doing right now is I have UR22 right output going into the right aux in of the Conrad Johnson preamp, Conrad's left and right output go into the left and right input of the DSP. 

I then loop back the OUT1 of the DSP to the left in of UR22. Is this setup correctly now?

I then mute different OUTs on the DSP while leaving the OUT 1 loopback channel always on. To measure different drivers. 

For some reason I am unable to set the levels correctly to make the measurements in this setup, the tweeters are especially problematic since REW keeps reporting that my ref in is way too low. 

Hoping you can shed some light on what I'm not connecting correctly here. Thanks.


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## JohnM (Apr 11, 2006)

I would take the loopback directly from the left output of the CJ, not sure what the DSP might be doing to the channels.


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## Twolions (May 21, 2014)

Very true. That's the puzzling part for me too. It has A and B channels. I guess if I'm going right aux in on CJ and then left CJ out to channel A input on DSP and right CJ out to channel B of the DSP, I should be good as long as I have channel B selected for OUT 1, but things don't seem to be working out well with that. I will try left out of CJ as you suggested. Thanks.


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## JohnM (Apr 11, 2006)

Don't forget you need to connect both the left and right UR22 outputs to the CJ left and right inputs.


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## Twolions (May 21, 2014)

Done. Making measurements, think I'm all set. Thanks so much for everyone's help on this.


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