Postcards from the Bleeding Edge
Friday, August 26, 2005

  Battling Hum...

If you got here from elsewhere, there's some updated information on this digital hash problem described here. Thanks for taking a look at this.

With an upgrade to the fabulous rme-audio multiface and ardour my studio has undergone a major facelift. I'm now trying to quiet all the instruments I have so to get a recording that can take advantage of 24 bits of 96Khz chocolately goodness.

I had some 60hz hum in my guitar interface, and ran a DI box on it to hopefully fix it. It didn't. I put my foot on the box while I'm playing - No more 60hz hum. Something about this guitar is interacting with itself, or I'm just an electrically charged individual, or my whole studio is a conductor or something....

OK, I can live with that fix for now, but the sound coming out of my XV-88 is driving me bats. At about -60db there's this unusual sound (depicted left with the gain boosted up to where you can see it - here's a sample of the sound: 96khz, 44khz) even when the device is idle, no processors on, etc. A balanced line output ought to be giving me -96db or so...



It's a weird sound, with peaks every 2 seconds per channel, each channel offset by a second.... It's not a 60hz hum at all, or even a harmonic of 60hz (I think)... it does have a harmonic on itself, too, with a cycle of about 24-26 seconds or so...

I long ago had just put a noise gate on it, and forgot about it, but I was trying to record a quiet passage without the noise gate late last night and I kept hearing it and I'm thinking that maybe something has given way within the XV-88 amp or processing module - or this is just a flaw of the XV-88's sound generation in general, or some sort of modulator was stuck...

I hear it on headphones if I listen closely, with nothing else plugged in.

I ran a new big fat wire to ground. No change.

I plugged in a electrical noise filtering box. No change.

I ran everything through a UPS. No change.

I unplugged the UPS from the wall. The whole circuit now floats - not connected to ANYTHING. No change!!.

What the heck is it? Now I turn the darn thing on and I'm painfully aware of the sound... help! I see that doc is talking about audiophilia - I'd love to be an audiophile if I can just get rid of my stinking hum... what to try next? running the ups to ground?
Gotta find a tool that will let me look closer at the frequencies than audacity...

Naturally I tried to contact Roland's tech support only to find that their support website was a push only system - no email contact and an email to supportatroland.com bounced... their website didn't have a tech support phone number listed - I finally found one on the back of the Roland manual and got to a support tech who asked the obvious questions and then forwarded the url of my blog to his manager.

I've got an update to where I'm at with debugging this problem here.

Monday I'm just going to take the unit into work and if it still has this noise and Roland tells me it's not normal - it's going into the shop.
 
Comments:
The "best" cure to eliminate hum is an audio transformer, but these are expensive and bandwidth-limited. The modern answer is an IC connected as a differential amplifier, and it is possible to use 3 ICs to "emulate" a transformer (but only in one direction). Grounding and noise problems can be infuriating, particularly in an unbalanced environment and I wish you luck.
 
Here's something else to check: levels are important, and you must have an adequate Signal to Noise ratio everywhere in your (analog) audio chain. To really get it right, each piece of analog equipment must see its proper impedance on both the input and the output. You can combine all of this by adjusting the output of each piece of audio gear until it clips, reduce it by 10 dB or so (headroom), and then design an audio pad (of the proper impedance) to decrease the signal to the level of the next input. When you pad the output down, you also pad the noise level down.

I'm adding this to the existing suggestions about shielding, grounding, UPS, and dimmers, all of which are important.
 
Dear Brenda:

Thank you for your thoughts!

It's not a hum per se' but a digital buzzing sound. I've heard similar noises before from poorly shielded sound cards in PCs, although never at such a constant (if low) volume. I put an parametric EQ at 800HZ with a 24db cut on it and that got rid of the sound nicely - at the expense of quite a lot of real sound...

All the cables in the chain are using gold balanced 1/4 I/O connectors with a couple XLRs as well.

Power to this building is on a long (100 foot or so) electric cable. I'd buy into ed skinner's antenna theory if I hadn't tried this with a standalone ups not tied to power at all. If there was some other device within a few feet that was radiating something but unless it's hidden under the house or being aimed at me by a soviet satelite (joke, joke) I don't know.

I'm otherwise a good 30 feet away from major power lines....

So, anyway, my big test is going to be moving all this gear to an entirely different location and that will be the kicker. In the meantime I'm going to try boosting the gain on this other sound module to see if I get the same noise out of it....

I'm thinking A) I might put some extra shielding inside the roland itself B) break out another device that generates sound to see what it does (I have but it's a -10 db, everything else is +4 - I think - I have to go through
 
Sounds like digital hash coming from the VX-88 itself. The electrolitic caps inside of it might be going south, there might be a broken shield on an internal jumper, etc.

Divide and conquer. Pull back the shield on the cable from the output, and SHORT IT, and see if the noise goes away.

--Mike--
 
Just checking out blogs for ideas to add to my site about phone video voip and other voip stuff. (I know its a boring subject) I liked your site
 
Hi,

I'm sorry for being intrusive in to your blog. But I am Melissa and I am a mother of two that is just trying to get out of an incredible financial debt. See my hubby is away in Iraq trying to protect this great country that we live in, and I am at home with our two kids telling bill collectors please be patiant. When my husband returns from war we will beable to catch up on our payments. We have already had are 2001 Ford repossessed from the bank, and are now down to a 83 buick that is rusted from front to back and the heater don't work, and tire tax is due in November.

I'm not asking for your pitty because we got our ownselfs into this mess but we would love you and thank you in our prayers if you would just keep this link on your blog for others to view.

God Bless You.

Melissa K. W.
To see my family view this page. My Family


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This blogstuff is great just looking around yours I have one too free debt management program I have a website dedicated to gettin people out of debt all free info free debt management program
 
Man, its been 3 years since your audiophile problem. You must have forgotten about it already!!
But if youre on the lookout for brands to namedrop, then it cant get better than these 5 big home audio.
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