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Howto - Distortion Measurements with REW
Howto - Distortion Measurements with REW
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Old 13th October 2021, 07:59 PM   #1031
phofman is offline phofman  Czech Republic
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Behringer UM2 is a USB fullspeed (12Mbps) soundcard. It sends/receives data every 1ms. IMO that is the 1kHz signal you see in your spectrum, very typical for fullspeed soundcards. The measurement signal with this card should differ a bit from 1kHz so that the results do not overlap with the 1kHz USB interference.
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Old 13th October 2021, 11:03 PM   #1032
trobbins is online now trobbins  Australia
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xrk971, that shows how well many cheap soundcard interfaces can do the job as a basic audio tool (ie. allow practical assessment of distortion products and any other signals down at a comparatively low noise level) without having to be aesthetically pleasing to the eye with a subterranean and flat noise floor with no extraneous signals poking out. I'd even expect that loopback using its own DAC output would be similarly as good with REW, especially for distortion testing as harmonic cancellation can be deployed and a test frequency away from 1kHz can be used.
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Old 14th October 2021, 03:44 AM   #1033
xrk971 is offline xrk971  United States
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Howto - Distortion Measurements with REW
I even tried using it as a DAC and the music coming out of it isn’t half bad. For $30, it’s got a lot going for it. There’s really no excuse saying measurement gear costs too much anymore.
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Old 19th October 2021, 05:16 PM   #1034
drinkingcube is offline drinkingcube  United States
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Finally got this working using a Focusrite Scarlet 2i2.

I think it was you, xrk, which suggested that you need to use T and R, not T and S, on a TRS for the input to the interface. After many attempts and finally reading the documentation *VERY* carefully, it seems the Scarlet 2i2 automatically configures itself to Line Input when you use a TRS (not TS) jack.

I was not able to get good distortion measurements using the direct out of the scarlet, decided to use my iPhone's DAC, seemed to work fine.

I did not use an attenuator, so max power I was able to send into this thing I believe is:

P = ( 9 * 9 ) / 8 = 10 W

It was fun playing around with the different gain stages: 2i2 preamp input, phone DAC, amplifier preamp.

Anyway, I am pleased with the results. Thanks for all the info in this thread!
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