Why such a waterfall! Help!

Lex_audio

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Good day, colleagues! Please comment on the amplifier measurement. I'm worried about the view of the waterfall.

. Where does this "trapezium" come from? Broke my head! What am I doing wrong? Or which settings are not correct? Thank you!
Oleg
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John Mulcahy

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Please attach the mdat file and a screenshot of your REW Analysis preferences.
 

Lex_audio

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Please attach the mdat file and a screenshot of your REW Analysis preferences.

***Thank you for responding. Yesterday, after much trial and error, the situation improved slightly and now the defect starts at -25 decibels. Uploaded files. Look here please.
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  • Soundcard.mdat
    4.1 MB · Views: 10

John Mulcahy

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That's normal, just an artefact of the low frequency roll-off. Better to use the normal Measure process than the soundcard calibration.

Your default windows are very narrow, 2 ms left and 5 ms right. Perhaps chosen for speaker measurements?

The measurement is a bit noisy, with quite a few mains harmonics.

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Lex_audio

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Thread Starter
Joined
Jan 17, 2019
Messages
10
That's normal, just an artefact of the low frequency roll-off. Better to use the normal Measure process than the soundcard calibration.

Your default windows are very narrow, 2 ms left and 5 ms right. Perhaps chosen for speaker measurements?

The measurement is a bit noisy, with quite a few mains harmonics.

View attachment 44009

***
Yes! I usually measure loudspeakers! Changing the window duration does not change the situation. And yes! This is a calibration, but if I do a normal amp measurement the waterfall looks the same.

I see noises! Didn't think of disabling smoothing. By the way, when measuring the loudspeakers, I do not observe such a defect.
So what conclusion can be drawn? Don't pay too much attention? Try to remove noise?
Thank you!
 

John Mulcahy

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Just ignore it. Waterfalls are not really relevant for measurements of electronics in any case. It would be worth trying to clean up the noise, assuming it is being picked up in the test leads. Different leads (screened or twisted pair) and lead positioning may help. You could look at the RTA in spectrum view to see how the noise pickup changes as you alter test lead type or positioning.
 

Lex_audio

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Thread Starter
Joined
Jan 17, 2019
Messages
10
Just ignore it. Waterfalls are not really relevant for measurements of electronics in any case. It would be worth trying to clean up the noise, assuming it is being picked up in the test leads. Different leads (screened or twisted pair) and lead positioning may help. You could look at the RTA in spectrum view to see how the noise pickup changes as you alter test lead type or positioning.
***
I replaced one of the interconnect cables, ground the computer and amplifier, and the amplitude of the noise decreased slightly.
Thank you very much! You helped me a lot. I may have to revise my measuring complex. In any case, this will have a beneficial effect on the measurement accuracy! Thanks again!
Oleg
 
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