Muff's Modules & More

Electronic Battle

Hello

Summary - please have a listen to this MP3 (it's only 93kB in size; see bottom of this post) and tell me if the background whine is typical when you connect an ordinary PC to a set of outboard analogue equipment via a USB audio/MIDI interface.

Detail:
I've got a dual-core PC running Windows 7. Connected to it via USB is an Alesis iO|2; inputs to that iO|2 are unbalanced from my mixer, whose inputs are various analogue non-MIDI synthesisers etc. all running off power sockets on the same mains ring.

I'm using Ableton Live - when I record the audio from the mixer (something I have hardly ever done before) I can hear an irritating background whine. It sounds like a tone from a switched-mode PSU so I went round the room and unplugged everything one at a time, first the audio leads from the instrument to the mixer, and then the mains lead which powered each instrument. I couldn't get rid of the tone.

There is a stack of fault-finding I can work through in the usual plodding and tedious manner, but if someone with more experience says "I recognise that - your problem is the [PC/audio interface/other] having [earth loops/ground noise/PC noise] - get yourself an [optically coupled interface/balanced line input mixer]" or some such, it would cut down my work and speed the problem solving up no end.

Thoughts welcome!

http://www.nitrogen.myzen.co.uk/whine.mp3

Babaluma · Posted: Sun Oct 23, 2011 2:57 pm Post subject:

no that's not normal at all. there is a problem. maybe grounding issues?

Electronic Battle · Posted: Sun Oct 23, 2011 3:40 pm Post subject:

Just me · Posted: Sun Oct 23, 2011 3:56 pm Post subject:

Read the potential between the grounds with an AC voltmeter. That will show where the trouble is. Usually.

jonah · Posted: Mon Oct 24, 2011 9:17 pm Post subject:

Pretty sure that's radio/cell phone noise. If you crank up the volume there should be a pulse to it. There's a video on YouTube of someone putting their cellphone in an anti-static bag to stop it. Pretty crazy. In my situation there wasn't anything in the immediate vicinity causing the problem that I could change and I wasn't going to line my walls with anti static material! I tried a lot, but only a power conditioner fixed it. I'm sure other brands work, but I tried a Furman rack and strip and each worked.

Just me · Posted: Mon Oct 24, 2011 10:31 pm Post subject:

Just listened to it with headphones. That sounds like driver issues in the PC. I've never heard a ground fault sound like that.

Zenn · Posted: Tue Oct 25, 2011 5:26 am Post subject:

My theory is: this is the switching power supply. The ultra-high harmonics caused by the square waves the power supply generates interfere with other stuff going on in the computer which somehow leaks into your audio. The only solution is an external audio IO which has its own power supply.

Electronic Battle · Posted: Tue Oct 25, 2011 10:59 am Post subject:

baboo · Posted: Wed Oct 26, 2011 12:59 pm Post subject:

Ok, I'll hijack the thread a little..
I have a similar problem-
My new audio I/O is powered with an USB bus from my laptop. When I'm sending it audio directly from my modular there is annoying hiss( more like little random clicks with varying pitch). when I send output from other devices eg. jealous heart there's no hiss. But when I record samples from modular to my MPC there is no hiss. So I'm pretty sure it's a grounding issue.
But how do I aproach grounding a
USB-powered interface??? is it even possible? would a headphone preamp module or something like malekko output help?

Electronic Battle · Posted: Wed Oct 26, 2011 3:39 pm Post subject:

I have made some progress - I think the problem is me!

I am uncertain as to how operate my mixer! I think I ended up with a low level signal feed and lots of mixer gain; the result was poor SNR and hence the background "whine" seemed to be at a much greater level.

I have made a few adjustments and will try again. I might need help on working my mixer next - an old secondhand 1980s vintage 8 into 2 with confusing send/returns!

Zenn · Posted: Thu Oct 27, 2011 7:38 am Post subject:

satindas · Posted: Sat Oct 29, 2011 4:23 pm Post subject:

@ Baboo
I' pretty certain that this IS an earthing problem. I had an identical noise problem with my laptop. When connected to my TC Electronics interface I had exactly the same noise. I've also encountered this noise many times in my work ... conference audio... The solution is to replace the laptop psu with a "universal", double insulated Power supply. These do not have an earth connection. This solves the problem every time so Baboo get yourself a new, double insulated psu or run of the battery.
@EB
Not sure how you could solve this issue with a PC and it seems strange that it's there in the first place. Your low signal level and high input gain won't help things but even at full whack that noise shouldn't be there. I think this is actually a digital ground problem but have read of this http://www.soundonsound.com/sos/nov04/articles/computerproblems.htm

Hope that all helps

Electronic Battle · Posted: Sat Oct 29, 2011 4:33 pm Post subject:

baboo · Posted: Sun Oct 30, 2011 2:04 pm Post subject:

Thanks guys, It is exactly as you said, the hiss disappears once I unplug laptop's PSU. I'll look around for a "universal" double shielded PSU and in the meantime I'll run on battery
It's motherfucking bacon yo

thanks a lot for your help!!! we're not worthy

I was a little scared about the hiss, but now it's ok! thumbs up

utom · Posted: Sun Nov 13, 2011 8:04 am Post subject:

I had the same hiss on my laptop, both when connecting the modular directly to line in and when connecting to USB via an external audio I/O unit. Pulling the powercord and going to battery power didn't help, however pulling an USB cable with an external hard drive and a printer did!