Distortion showing in measurements

miniDSP and AV Nirvana
jimmykaka

jimmykaka

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Preamp, Processor or Receiver
Marantz SR6012
Universal / Blu-ray / CD Player
Panasonic DMPUB400 4k UHD
Streaming Subscriptions
XBOX 1 S White, FIIO Portable media player + DAC
Front Speakers
KEF 2005.3 Egg
Center Channel Speaker
KEF 3005SE
Surround Speakers
KEF 2005.3 Egg
Front Height Speakers
Klipsch CDT2650-C in ceiling Atmos x 2
Rear Height Speakers
Klipsch CDT2650-C in ceiling Atmos x 2
Subwoofers
KEF Kube 2
Screen
Samsung JU6510 48" White 4K Curved
Remote Control
Harmony 650
Hi all hoping for some help. Getting back into REW after installing some room treatments.
Today on the waterfall graph on all 7 bed layer speakers I noticed some odd results landing at 1/2/3/4k and so on.
I decided to check distortion graph and it showed up there too.

Can anyone suggest what might be causing this.

Using UMIK1, Intel NUC 6CAYB , Marantz Cinema 40.
So far I've tried adding a powered USB hub which I didn't have on when I ran these initial measurements, that slightly reduced the distortion.
I've swapped out the USB between hub and UMIK1.
Ive tried running the speaker directly into AVR bypassing the power amp.
I've looked into drivers on windows and that seems as up to date as I can get it, although I did have an issue where it failed to install a driver, windows says it's on the most up to date driver (2021) but it seems there is another one available from 2023.
I've checked formats and set PC and REW to 48Khz.
I've changed the USB input on the NUC.
I cant think of anything else.

Any help would be appreciated. Thanks in advance.



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USB mics are supplied from the USB interface. The USB power picks up interference from the USB data clocking. That interference can be strong enough to get into the analog signal the mic receives. Different ports or hubs or shorter USB cables might help.
 
John Mulcahy said:
USB mics are supplied from the USB interface. The USB power picks up interference from the USB data clocking. That interference can be strong enough to get into the analog signal the mic receives. Different ports or hubs or shorter USB cables might help.
Click to expand...
Thankyou for the info.
Could potentially be the length of the USB cable between the mic and hub or mic and NUC.
I have a 5M USB cable between the NUC and where I am measuring. Then the UMIK1 cable is 5M too but I tried a shorter one on that and it didn't make a big difference.
I'm going to give my laptop a try, I can have that in the same room as the UMIK1 and use HDMI out from my laptop via a 10m fibre HDMI to my AVR as that's in a room upstairs.
 
John Mulcahy said:
USB mics are supplied from the USB interface. The USB power picks up interference from the USB data clocking. That interference can be strong enough to get into the analog signal the mic receives. Different ports or hubs or shorter USB cables might help.
Click to expand...
So I tested out REW on my laptop and had the same distortion at 1/2/3khz etc. And a lot more low end distortion between 100-400hz.

1000006760.jpg



So this tells me that the problem is likely the USB cable.
My problem is that cable is routed from the AV rack where the HTPC & AVR is in the room above my cinema, through the floor and down the back of an MDF pillar I made to house my side surrounds. So it has to be long.

I have two HDMI to the TV from the AVR however they are directional due to fibre so that ruled out connecting my laptop downstairs with the UMIK1 plugged in and running sweeps that way with a short cable between laptop and UMIK1.
I can't think of a way around this issue!

One thing I have noticed and I'm not sure if this makes a difference is the issues are showing up in the noise floor measurement. How much of an effect is this going to have on running room EQ in either REW or Dirac?

Any help or suggestions on how to minimise this issue would be greatly appreciated! Would some kind of power injection work?

Thanks
 
You might consider using the Generator function to create a sweep.wav file, with a timing reference, that you can play thru your entire signal chain... Put the sweep.wav file on your player system... Then take your laptop to where you want to measure, using only the mics usb cable... Use your player software to play the sweep and use your laptop with mic to make the measurement... :T I am sure there are better and more detailed instructions on how to do this somewhere around here... :dizzy::justdontknow:
 
Thankyou both for your input and suggestions, great idea. I wonder if running two separate instances of REW could also work? One running the sweeps from the HTPC (I could use the TV in my cinema to view that) and a separate instance of REW in my cinema on the laptop with the Mic attached to it. Certainly worth a try!! @ddude003
@JStewart
 
Should work as long is you have a timing reference on the signal generation side... And why make things any more complex then they need to be... Just put the sweep.wav file on a jump drive, most AVRs and streamers will play directly from them...
 
Yeah I'll make sure to add acoustic timing reference. I thought the shield might be a good shout as I can drop the file straight to it over the network and I also have some demo material as well as a 'spatial audio' calibration kit that Technodad made, not sure if you've heard of it. It may even have some sweep files on it I can't remember, might not have any timing reference on it though. Thanks for the reply!!
 
ddude003 said:
Should work as long is you have a timing reference on the signal generation side... And why make things any more complex then they need to be... Just put the sweep.wav file on a jump drive, most AVRs and streamers will play directly from them...
Click to expand...
I'm not able to find a way to add any sort of timing reference to the signal generator? Any suggestions?

*Edit* I've just run a test with my laptop and a 1M long USB cable as well as the 5M long one. Those issues are still there. Could this be a problem with the UMIK1? I saw on the MDSP forums that a batch of them (not my batch apparently) had some issue that presented itself like this.
 
Last edited:
John Mulcahy said:
USB mics are supplied from the USB interface. The USB power picks up interference from the USB data clocking. That interference can be strong enough to get into the analog signal the mic receives. Different ports or hubs or shorter USB cables might help.
Click to expand...
I've just run a test with my laptop and a 1M long USB cable as well as the 5M long one. Those issues are still there. Could this be a problem with the UMIK1? I saw on the MDSP forums that a batch of them (not my batch apparently) had some issue that presented itself like this.
 
Screen Shot 2025-03-08 at 5.08.03 PM.png
 
Bottom center check mark "Add Timing Ref"...
 
ddude003 said:
Bottom center check mark "Add Timing Ref"...
Click to expand...
Ah that would be why I can't find it! The option isn't there for me, I'm on the latest version 5.31.3 too!
 
Apologies I was on 'play' instead of 'save to file' thank you.
 
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