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Discussion Starter · #1 ·
My "sound card" (actually an outboard DAC connected via USB interface) has a system delay of about 500ms. This can be easily seen by looking at the "scope" graph when taking a loop-backed measurement of the DAC plugged into the computer's line-in.

However, REW is unable to detect this delay and instead sets the system delay to 0ms. This causes all the resulting measurements to be incorrect.

Is there a way to get REW to detect this relatively large system delay?

Thank you for any help in advance!

Version: Mac Version 17, beta 5
Computer: MacMini 2009
Sound Card: Mac USB audio output to NAD M51 outboard DAC
Input Mic: UMIK-1
Loopback Measurement: NAD outboard DAC to Line-in.

p.s. A second problem is that I am measuring with UMIK-1, which is a USB-interfaced microphone. A loopback measurement of the soundcard will capture the delays induced on both the outgoing and incoming signal (or in my case, the outboard DAC + the on-board DAC used to process line-in). The measured incoming delay will not be the same as the input delay of the USB-interface UMIK-1 microphone. This seems like an insoluble problem for the moment, but I thought I would mention it in case REW developers are interested in making improvements for USB interfaces.
 

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To use a loopback connection as a timing reference you need to tick a box in the Analysis preferences. A loopback can't be used with USB mics, but there is a way around that by generating a reference signal on one output channel that is connected to a reference speaker or driver and generating the test signal on the other output channel a short (and known) time later, measurements can then be made relative to the reference speaker/driver. That hasn't been implemented, but it is on the list of things to do.
 

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Discussion Starter · #3 ·
John,

Thank you for such a quick response!

My question was actually in relation to producing a sound-card calibration file, so the USB microphone was not yet in play. Does this system delay play a role in the generation sound-card calibration file, or am I mistaken?

As to the use of loopback time reference measurements with USB microphones, here is what I have done. It seems to work for me. Thoughts?

1. Using "LineIn", I route the UMIK-1 microphone to Soundflower (2ch)
2. Under "Audio MIDI Setup" I create (click + button, bottom left) an Aggregate Input Device that mixes 'Built-in Input' with 'Soundflower (2ch)'
3. Also in "Audio MIDI Setup" I then click on the "Buil-in Input" device and mute channel 2. The UMIK-1 USB mic produces input only on Channel 2. The result is the aggregate has line-in on channel 1 only, and UMIK-1 on channel 2 only.
4. Select "Aggregate Device" for the input under REW.
5. Set Input Channel to "Right"

With this configuration, If the input channel is set ti Right, the SPL meter responds to ambient noise picked up by the microphone but does not register any tone generated by the signal generator. If the input channel is set to Left, the SPL meter shows steady signal from the signal generator, but does not register any input from the microphone.

As long as the loop-back timing calibration uses the opposite channel as the measurement channel (which I presumed was the case), then I thought this would detect the system delay.
 

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System delay doesn't matter (within reason) for the soundcard calibration, it is ignored.

A loopback via an aggregate device may well work if OS X maintains relative timing of the individual devices, which is a reasonable expectation. Easiest way to check is to make a few successive measurements and see if the system delay figure is consistent.
 

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Hi

I have the same problem

I use miniDSP 2*4
Umik 1
USB DAC (beresford Caiman)
Computer
REW5
Windows 7 - (thread starter uses OSX)

can someone confirm that it is not possible to meassure time delay between drivers at the moment with this setup - any other software that can do it right know ?

John: Do you know when there would be a solution to that problem ?

Kind regards from Demark
 

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Correct, you cannot measure time delays between drivers with a UMIK-1 on Windows with REW. You might be able to do it with HolmImpulse, that has a mode that tries to keep the soundcard input active between measurements.
 
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