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Discussion Starter #1
I'm trying to figure out whether there's something wrong with my connection/set up or if my DSP isn't adding delay correctly now.

I've a Sound Devices USBpre 2 sound card that has internal loopback function.

Connection is the following:
- Right channel output to DSP
- Left input to mic
- Internal loopback from left output to right input

My settings in REW are like the following:


Looking at the ETC and impulse, it looks like the timing reference works:




But there two matters:

1. Delay in DSP doesn't change anything. Might be a problem with the DSP though. After all, I'm seeing difference in delay between drivers in speakers. So can I conclude from that the DSP must be the problem?

2. If I remove the internal loopback I get a message that the level is too low, but the timing/arrival is still the same. How can that be?
 

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Your timing reference output is selected as the right output (2) though, shouldn't it be the left (1)? Crosstalk might be enough to keep it working without the loopback connection.
 

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Discussion Starter #3
Your timing reference output is selected as the right output (2) though, shouldn't it be the left (1)? Crosstalk might be enough to keep it working without the loopback connection.
The picture was wrong. I've been trying different setups and forgot to set it correctly when taking the print screen. Sorry.
Attached the correct one which was used in the previous showed measurements.

Can you elaborate on what you mean by crosstalk being able to make it work without loopback connection?

Here's from the manual concerning the internal loopback function:

Input 2 Loop Source
Input 2 has an additional source labeled LOOP. This input source does not correspond to any physical
connections on the USBPre 2. When LOOP is selected, input 2’s source is derived from the left
channel of the computer audio signal (post digital-to-analog conversion). The input 2 Gain Control
affects signal The Output Gain Control does not affect the level of the signal going in to input 2.
The LOOP source is useful for test and measurement applications where a reference signal is required
to be routed back to an input.
 

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Even if you haven't selected the loop connection there will be some internal crosstalk between the channels of the soundcard, that might be enough for the loopback code to detect a reference signal.
 

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Discussion Starter #5
Thanks John.

Seems like the issue here is the DSP, which isn't responding to delay right now. I'll experiment some more.
 
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