REW Loopback connection setup

[neo_2017]

I'm trying to understand how to setup the Loopback connection in REW, so i can take measurements with an accurate timing reference.
I have the following gear:

• Behringer UMC404HD
• Behringer ECM8000
• Topping PA5
• Laptop

The following image is how i would configure everything:

1. Connect Mic to UMC404HD (XLR to XLR)
2. Connect Laptop to UMC404HD by USB
3. Connect the Loopback connection on UMC404HD => Line input to Line Output => 6.35mm jack to splitter 2 x 6.35mm cable
4. Connect L/R outputs on UMC404HD to Amplifier 6.35m inputs => 2 XLR to 6.35mm cables
5. Connect Amplifier speaker outputs to speaker

Is the above Ok? Am i'm missing anything, or is anything incorrect?
Thank you in advance!

 

[Wayne A. Pflughaupt]

Re #3, you can’t use the Insert connections. They are for inserting an outboard processor into the signal chain, such as a compressor or noise gate. The loopback needs to be connected between a rear-panel output and a front-panel input.

Re #4, the 6.35 plugs need to be TRS.

Regards,
Wayne

 

[neo_2017]

Thank you very much for your reply.

On #3, you mean like this?
Using a XLR to a 6.35 splitter cable?

 

[Wayne A. Pflughaupt]

I'd just go 6.35 to XLR. Never seen anyone use a splitter like that.

BTW, the 6.35 output jack on the Behri has to be TRS - check the manual to make sure.

If not, you can just do 6.35 TS between the output and input. The inputs look like combination jacks that will accept 6.35 TS plugs as well as XLR.

Regards,
Wayne

 

[neo_2017]

I'm sorry, i'm still confused regarding the loopback connection

What is the proper way to do it?

1 - Two rear panel outputs (L/R) to 2 Front Panel inputs (Input 2 and Input 3)

2 - Two rear panel outputs (L/R) to 1 Front Panel inputs (Input 2)

3 - One rear panel output (L or R) to 1 Front Panel inputs (Input 2)

PS: Thank you for the tip on TRS vs TS, i didn't knew there were two types of 6.35 jacks

 

[sm52]

Post #3 is almost correct. From one output (for example, L) there must be a wire to the input (for example, Input 2), and the same wire must go to one channel (for example, L) of the amplifier. The microphone is correct.

 

[neo_2017]

I finally have everything working:

1. Mic to Interface => XLR to XLR cable
2. Laptop to interface => USB cable
3. Loopback => Main R OUT to Input 2 => XLR to XLR cable
4. Interface to Amplifier => Main L OUT to Amplifier Channel 1 => XLR to XLR

UMC404HD Soundcard calibration result:

Thank you for all the help !!!

 

[sm52]

1. Loopback => Main R OUT to Input 2 => XLR to XLR cable
2. Interface to Amplifier => Main L OUT to Amplifier Channel 1 => XLR to XLR

So wrong.

• Loopback => Main R OUT to Input 2 => XLR to XLR cable
• Interface to Amplifier => Main R OUT to Amplifier Channel 1 => XLR to XLR

That's right. That is, you need a Y-cable XLR-XLR-XLR

 

[jtalden]

Post 7 looks correct to me.
The left channel is the measurement channel.
The right channel is the REW loopback signal. We want that going back into REW and not out to the speakers.

 

[neo_2017]

In REW documentation, on the "Calibration Panel " section, its stated: " Calibrate... starts a process of measuring the interface response via an external loopback connection".
Given that the soundcard is configured via Loopback, and its correctly configured as the above image shows, i assume the connections are correct.

@Wayne A. Pflughaupt, could you please clarify?

 

[sm52]

The left channel is the measurement channel.
The right channel is the REW loopback signal.

On the one hand, it will work. On the other hand, if there are differences between the start time of the impulse in the output channel L from R (cheap sound cards), will the measurement be accurate?

 

[jtalden]

In REW documentation, on the "Calibration Panel " section, its stated: " Calibrate... starts a process of measuring the interface response via an external loopback connection".
Given that the soundcard is configured via Loopback, and its correctly configured as the above image shows, i assume the connections are correct.

@Wayne A. Pflughaupt, could you please clarify?

Sorry, I mistakenly assumed you were interested in loopback timing feature for your measurements.

The soundcard calibration process is a different issue. To do that just remove the mic and run a cable between output L and Input 1. No other cables are needed. After the soundcard calibration is completed, the cable is removed, and the mic is attached back into input 1 for measurements.

 

[jtalden]

On the one hand, it will work. On the other hand, if there are differences between the start time of the pulse in the output channel L from R (cheap sound cards), will the measurement be accurate?

The loopback timing is just a reference point in time that is consistent. It matters not that it may have a fixed offset between channels on very cheap soundcards. It is the only the consistency of the timing reference that matters.

 

[neo_2017]

Sorry, I mistakenly assumed you were interested in loopback timing feature for your measurements.
The soundcard calibration process is a different issue...

I'm actually interested in both:

1. Soundcard calibration
2. Loopback timing features

I assume (1) is Ok, as the soundcard measure seemed ok.

Regarding (2), are the connections correct for loopback timing feature for measurements?

 

[jtalden]

Yes.

 

[serko70]

Yes.

Sorry to jump into an old topic....If my speaker output is not directly connected to the mic audio interface i.e. using another USB port on the PC, is there still a way to utilize loopback timing reference?

 

[jtalden]

No.

 

[John Mulcahy]

Depends what you are using, if you have a spare output on whatever is driving the speakers and a spare input on whatever the mic is connected to you can have a loopback between them.