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My First Loop Back with REW on a Mac. It doesn't look right!

HionHiFi

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#1
So I'm embarking on measuring components in my audio system. I'm using a Macbook Pro, MOTU M4 as the audio interface and REW as the measurement software.

I've watched several loop back test, and setup videos, but my results aren't coming out right but I don't know what I'm doing wrong.

When I do the "Soundcard Calibration" I get this error msg.

REW_Screenshot.jpg


My loopback chain is:
Output Right 4 on M4 into Input Right 4 on M4. Connected with TRS Balanced connectors. I believe these are stereo. Could that be the problem?

1528989651_828467.jpg


When I run the calibration test I don't see any input level on my M4. I can see the output though. Any thoughts on how to get a proper loopback done on a Mac?
 
Last edited:

JohnPM

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#2
If there are 4 input channels and your loopback is on channel 4 then you should probably select channel 4 as the REW input channel, currently looks like channel 2 is selected.
 
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HionHiFi

HionHiFi

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Thread Starter #3
Yes there are 4 channel inputs.

Output Device: M4
Input Device: M4
That is what is selected.

Here's what I see.

Input device: M4
Input: To Computer (In 1)
Channel: Right
Output device: M4
Output: From Computer
Input RMS target: -12.0 dB
Actual RMS at 1 kHz: -121.8 dB
Sample rate: 44100 Hz
Input volume: no control, Sweep level: -12.0 dB
20 Hz .. 20 kHz flatness: +20.5, -47.7 dB
-3 dB points: 995.9 Hz, 1.003 kHz

Should I be modifying the Loopback Input? It only shows L or R, but those are piped to input 1 and 2 respectively.

Untitled.jpg



Here's what I see.

Input device: M4
Input: To Computer (In 1)
Channel: Right
Output device: M4
Output: From Computer
Input RMS target: -12.0 dB
Actual RMS at 1 kHz: -121.8 dB
Sample rate: 44100 Hz
Input volume: no control, Sweep level: -12.0 dB
20 Hz .. 20 kHz flatness: +20.5, -47.7 dB
-3 dB points: 995.9 Hz, 1.003 kHz

65565875-3E47-4987-8B24-F1B9D12DE023_4_5005_c.jpeg
 
Last edited:

JohnPM

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#4
That is just noise, you are capturing an input with nothing on it. If there are two input selections (In1 and In2, for example) then the rear panel is probably In2. Also worth checking that there is a signal on the output you are using, by connecting it to your system, for example.
 
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HionHiFi

HionHiFi

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Thread Starter #5
That is just noise, you are capturing an input with nothing on it. If there are two input selections (In1 and In2, for example) then the rear panel is probably In2. Also worth checking that there is a signal on the output you are using, by connecting it to your system, for example.
Ok. I have 2 Mic inputs (1L & 2R) on the front panel and 2 line inputs (3L & 4R) on the back panel. Nothing is plugged into the front Mic inputs.

I have my powered speakers connected to the MONITOR outputs via TRS. I can hear the tone being generated by REW on my monitor speakers.

I found the MIDI Mixer on my Mac which might have something to offer.

Screen Shot 2020-09-29 at 8.09.38 AM.png


Screen Shot 2020-09-29 at 8.09.28 AM.png
 

JohnPM

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#6
So is there a "To computer (In4)" input in the REW list? What input choices are there? Have you tried them all?
 
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HionHiFi

HionHiFi

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Thread Starter #7
Ok, I think I've made some headway. The graph looks hideous, but at least I'm getting Output and Input levels which means my I/O chain in being routed properly. Now I need to manipulate the graph to display better...

Test0005_96kHz_OM4_IM4_OFrmCPULFE_IToCPUin1-4.png


Here is the correct setup for a Mac.

Question: How to get more level out of the input, or bring the output volume down? When I increase the sweep level, the input doesn't increase much and remains 6-12db lower than the Output level. How do you increase the input sensitivity?

Screen Shot 2020-09-30 at 8.16.33 AM.png



REW_Measurement_DB Headroom.png
 
Last edited:
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HionHiFi

HionHiFi

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Thread Starter #9
Thanks to your help I finally got it.

I had to adjust the input volume on Output 4 on my Mac, MIDI Audio Devices to match or get close to the Output volume of the Sweep level.

Screen Shot 2020-09-30 at 2.44.04 PM.png


Anyway, here's what I got so far.

MOTU_M4_Distortion2.png
 
Last edited:

Blumlein 88

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#10
Just thought I'd say it is great to have John here to help out with his software. And some delicious software it is too.
 
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HionHiFi

HionHiFi

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Thread Starter #11
Just thought I'd say it is great to have John here to help out with his software. And some delicious software it is too.
Totally. He's dependable. I'm appreciative. Now I'm getting into the electronic component measurements piece of the software, for Streamers, DAC's, Amplifier, Preamplifiers, etc.
 

restorer-john

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#12

RayDunzl

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#14
I'll retest and see if I can recreate it? In the meantime though, how does one fix this issue?
Run the sweep tone to 22kHz and see what happens at 20kHz.
 

RayDunzl

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#16

JohnPM

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#18
If the sample rate selected in Audio Midi Setup is different to the rate selected in REW the OS will resample the data to match the REW rate.
 
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HionHiFi

HionHiFi

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Thread Starter #19
I tried the test again this evening and couldn’t get the frequency response past 20kHz. There’s a >10db drop off after about 15kHz.

I changed the frequency range to 10-22000kHz. Same results.
 

restorer-john

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#20
tried the test again this evening and couldn’t get the frequency response past 20kHz. There’s a >10db drop off after about 15kHz.
If it really drops like a stone after 15KHz, it's utterly useless for testing. Something isn't right. Check the sampling rates on the software, the device driver/app match as per John's advice above.
 
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