USB audio interface spontaneous sawtooth oscillator - help!

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unfa
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USB audio interface spontaneous sawtooth oscillator - help!

Postby unfa » Wed Nov 09, 2016 12:34 am

I got a new interface a few months ago: Behringer Uphoria UMC202HD

It's a USB-powered class-compliant device with 2 inputs with JACK/XLR combo sockets and 24bit/192 kHz input fidelity.

It also appears to feature a spontaneous sawtooth oscillator that likes to switch on and play atonal solos over my recordings when I couldn't desire less to hear (and capture) them.

Watch this and wait for 0:25 to hear what I mean:
https://www.youtube.com/watch?v=Dbn0GhftXXs

But first a bit of the background story.

After a month of using this device I sent it back to the store, because of that behaviour.
The store have tested my device (using Windows-powered machines I guess) and didn't notice any problems.

The interface seems to literally have a built-in sawtooth oscillator that is randomly turning on and changing pitch smoothly (sometimes it sounds like phase modulation even) ranging from slow clickling to high buzz of the sawtooth.

Also it's constantly feeding low frequency pulses into all outputs, regardless of the set volume. It's very subtle but it's there.

I believe this is related to the ALSA drivers, the device is USB compliant and I'm using it under Linux Mint 18. First I tried with the MATE version, now I'm continuing with the KDE5 version, and the problems are still here, more prominent then ever.

Sometimes restarting (reconnecting the USB cable that's also the only power source) the device helps for a while, sometimes it doesn't.

Heres's another little sample of how this sounds like. You can hear that I turn up the gain after a while:
https://soundcloud.com/unfa/umc202hd-sa ... neous-solo
It was the first time I captured this phenomenon.

When I'm not laughing - I'm pulling my hair out because of this. Messing with ALSA mixer for the device doesn't help.

Have you experienced similar problems with this or any other devices?

Could this be a device driver problem? Should I try an older kernel?

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Re: USB audio interface spontaneous sawtooth oscillator - help!

Postby gimmeapill » Thu Nov 10, 2016 12:16 pm

I used to have an interface that would sometimes go nuts in a similar way when I was pushing it to the limits and/or depending on what I was connecting the analog outputs to (probably a grounding issue in my case). No idea what can be the root cause in your case, but I would first investigate the HW & connectivity, before incriminating a desktop environment.

So, just to get this out of the way: Try another USB cable. Don't use the garbage one that came with the card no matter how good it looks (best is probably to get a new USB 2 certified cable). The shorter and the more shielded, the better.

Next, make sure you're using the best USB port on whatever computer you're connecting to
(that might be tricky to find out, you might need to look at the motherboard schematics).

If that doesn't help, try to reproduce the issue when analog outputs and inputs are disconnected (just a headphone plugged in directly to monitor). Disconnect any potential AC powered mixing table, 48v power supply, etc... with the notebook running on batteries if relevant.
If the issue is caused by a grounding or other electric interference causing the card converters to go crazy, you should should hear it there.

Next, if might be useful to test at different settings (bite rate, frequency, latency etc...). If its really the card, you may find some behavior differences there.

As for the drivers, well, the easiest would maybe to try with a live distro.

Good luck ;-)

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Re: USB audio interface spontaneous sawtooth oscillator - help!

Postby unfa » Thu Nov 10, 2016 1:36 pm

Thank you, gimmepill!
You gave me some great tips for troubleshooting, hopefully I can get the interface to work as it should or at least prove that it's damaged and get it replaces eventually.

I've made a spreasheet to test and list all variables I can about these problems.

I'm normally connecting the interface through a hub into a USB 2.0 port (I also have two 3.0 ports on the other side of the laptop - Because there's more ports there than on the 2.0 side - I guess these ports are soldered right into the motherboard, not onto some remote helper board.

2 new things I noticed about the problems:

1. The mic input ocasionally gets a loud impulse spike, like a single cycle of a sawtooth waveform. This sounds new to me - I didn't hear this until yesterday.
2. If I disconnect the power from the interface, while having the monitors powered on - I get a loud downward sawtooth pitch slide - I wonder if it's generated by the same element that causes most of the trouble - this behaviour is what I saw from the very beninning, but never thought it might be connected.

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Re: USB audio interface spontaneous sawtooth oscillator - help!

Postby gimmeapill » Thu Nov 10, 2016 3:41 pm

That USB hub is a deal breaker. You really have to plug directly into the fastest port to ensure decent performance.
Hubs are fine for low bandwidth stuff like midi controllers, mouse & co. But NOT for soundcards ;-)
If you have both USB2 and USB3, then the best bet should be one of the USB3 ports.
Forget about that urban legend that says USB3 is bad for audio - they are the fastest ports you can get on most computers even if you use them at USB2 speeds (since USB3 ports are unlikely to go through an internal hub). I suspect the issues reported were with first gen hardware and drivers and are nowadays more of a corner case.

Anyway, back to the topic: Those symptoms look more an more like a connectivity problem.
So: cable check, direct connection to the fastest ports and you should hopefully see some improvement...

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Re: USB audio interface spontaneous sawtooth oscillator - help!

Postby CrocoDuck » Thu Nov 10, 2016 10:25 pm

unfa wrote:Watch this and wait for 0:25 to hear what I mean:
https://www.youtube.com/watch?v=Dbn0GhftXXs


Do you mean 2:25? I have extracted the audio and had a look at it.

Image

It looks as a sawtooth indeed. Pretty weird. I once witnessed port related noise when using my company MacBook Air. I had a USB hub on a port for mouse and keyboard and an FCA1616 on another USB port. When moving the mouse I was able to see noise appear in the spectrogram. However, it was much more subtle. It also strikes me that the base frequency is low, around A4. The port noise I observed was based at few kHz (If I remember correctly).

I don't see how it could be a software issue: why sawtooths should be generated around? Still, the ways of bugs are infinite.

Stupid question: does it happen at random regardless of the software you are running? Does it happen only if jack is running?

Let us know how it goes with the ports troubleshooting. Ports / hardware issues seems the most likely cause to me, although I never saw this specific kind of noise appearing for that particular reason.
Check my Linux audio experiments on my SoundCloud.
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Re: USB audio interface spontaneous sawtooth oscillator - help!

Postby unfa » Sat Dec 03, 2016 5:05 pm

I've done lots of tests (using a spreadsheet also, yay!) since I last posted in this thread and I found out the sources of all the problems.

1. The random sawtooth solos are coming from the Behringer B-1 microphone - I bought this one used from a friend. Today I finally got the sawtooths again when having another condenser mic (Behrnger C-2) around for testing - C-2 made no noises. And when I actually flipped the "-10 dB" switch on the B-1 - the sawtooths also got queter, so I know they are happening inside the mic, in it's internal circuitry somewhere before the built-in -10 dB attenuator/ highpass filter. Same goes for the random impulses - they seem to be in the mic. I was using a (noname) dynamic mic a bit lately and non of the problems bothered me when using it.

I recorded a short video about this:
https://www.youtube.com/watch?v=lRwgYy3JJv4

2. The constant beating went was caused by a USB device interference. I was using an USB 2.0 hub, and also had a Wacom Bamboo tablet connected to the same hub as the interface. Once I disconnected the Wacom tablet - the beating has gone right away. I decided to dedicate a separate 3.0 port on the other side of my laptop to the UMC202HD interface and since I did that - the beating is nonexistent.

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Re: USB audio interface spontaneous sawtooth oscillator - help!

Postby CrocoDuck » Sun Dec 04, 2016 8:51 pm

That's pretty interesting. I wonder whether there could be a feedback loop of some kind involving the mic port of the soundcard, maybe through improper grounding and phantom power. This might yield to self oscillation of the internal circuitry of the mic that could be distorted by slew rate...

Or maybe not. Just thinking out loud. Glad you figured out the source of it.

EDIT: I suggest to have your mic feature a solo on your recordings :D .
Check my Linux audio experiments on my SoundCloud.
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