I'm picking up bad vibrations...

October 21, 2010 9:22 AM

Very annoying noise in monitor speakers following connection of external firewire sound card to new Mac Book Pro. Is it "ground hum"? Don't think so.

Hello.

I'm an amateur music maker. A few months ago I had a setup based on Windows. My (Dell) Windows XP machine was connected via firewire to an external M-Audio Firewire 410 sound card. In turn, the sound card was connected to a pair of Fostex PM-1 monitors. All sorts of other bits 'n'pieces were attached too, but the conclusion of this part of the story: everything worked fine. Perhaps a teeny tiny bit of audible noise of some kind in the PM-1 monitors, but hardly noticeable.

Wind forward a few months to now. I've moved house (so different house, different power strips, and I've splashed out on a fancy spancy new Mac Book Pro.

If I set up my hardware as follows: I have no problem. Laptop connected to power strip (using regular Apple PSU), M-Audio firewire 410 connected to Mac Book Pro (using new, recently brought 9 pin to 6 pin cable), PM-1s connected to M-Audio 410 (via, incidentally, what I *think* are 'balanced' 1/4 jack to XLR cables).

But as soon as I attached anything else to my Mac Book Pro - for example, an external monitor (which I really need to use) via MBP mini display port, or anything via USB (got a bunch of USB devices running off a hub) - the noise begins. So, I'm pretty sure I know what 'ground hum' sounds like - and it's not that. For absolute clarity, I checked this - linked from here - and it's really definitely *not* that (which is what I know 'ground hum' to sound like). So what is the noise? it's...

- screechy. It sounds like data. It's not so loud that no music is audible, but it's plenty loud enough that you can't really bear to have the monitors on. (In fact the only crappy workaround I currently have is to have the PM1-s turned right down, so I can just about hear the music, and just about not hear the noise)

- entirely dependent on whether or not my MBP is playing back 'sound'. So in other words: imagine I'm working on my laptop; not making music; just using Chrome to look at the interweb. I'm hanging out in gmail (I don't get out much), and one of my friends binks me via gmail instant messaging. Just prior to when they messaged me: the sound of silence. Almost no audible noise coming from the monitors. The moment they message me: a split second before, the screeching starts - then the system instant message sound - then, if the system doesn't need to play any more sound, after a few seconds, the screechy noise disappears again.

In a similar vein, if I fire up Logic Pro, the screeching noise starts the moment I launch it, and stays constantly. (It's as if somehow the 'need to make sound' is permanently activated whilst Logic is open). Close logic: screeching disappears.

Couple of other bits of pertinent information: if I connect headphones to my M-Audio 410, there is *no* screeching noise. This seems completely bizarre to me, but I'm no electrical engineer! - how can there be zero screech coming from the headphones, whilst I'm sitting there and at the exact same time hearing it coming from the monitors attached to the same sound card?

Lastly: I tried, as an experiment, when reading a bit about 'ground lift', to 'break the ground' on my PM-1s. Specifically - I live in the UK - I turned around the three pin plug 180 degrees on the power plug and plugged it back in with only two pins; without the earth pin. Bingo - instant solution; zero noise in the monitors, heaven. But I understand that's dangerous? - so I swapped it back. So I did some more Googling and just bought a couple of these thinking that I was being sensible - breaking the ground in the signal, rather than the power (which it seems like is what you need to do). But.... they don't work at all.

So, I've read a ton of stuff online; tried a ton of stuff; read previous Ask Mes; I can't see an exact description of, or solution to, what I'm experiencing here. Apologies for the length but I wanted to try to provide as much information as possible. If anyone can help I will be HUGELY grateful!

posted by Hartham's Hugging Robots to Computers & Internet (10 answers total)

Have you tried other sound interfaces? I use a Presonus Firebox for doing about the same thing as you on my Macbook Pro and i get no hum or digital garbles. My brother had his USB M-Audio interface die on him, and it was doing the same thing you are describing before it finally just crapped out. If you can borrow another interface, you should try that.
posted by alextprice at 9:43 AM on October 21, 2010

Have you tried other speakers? Like alextprice says, it's possible the line outputs of your 410 are going bad? Have you tried connecting your speakers to other outputs?
posted by Monday, stony Monday at 10:11 AM on October 21, 2010

Seems to me that the cables are picking up interference. Try different cables. Try moving the cables. Try different outs on the 410, try running the 410 to a mixer or something first before running the cables to the speakers.
posted by empath at 11:39 AM on October 21, 2010

Response by poster: alextprice: I'd definitely try another sound interface like a shot - if I knew someone nearby who has one. But I don't, sadly. I could buy a new one, BUT i) I don't particularly want to spend the money if there actually isn't any thing wrong with my current box (I'd much rather put it towards some new monitors), and ii) I'm worried there might be a chance that I'd spend the (not insignificant) money on a new box only to discover I still have the same problem.

Monday, stony Monday: I don't have any other monitor speakers. However: I have already tried all the line outs of the 410 - same problem. I've *also* tried attaching the 1/4 jack cables that go to the monitors to the *headphone* sockets on the 410: yes, there's a strange mono / stereo thing going on there, but the freaky thing is: same noise - even though when you connect headphones to the same socket, no noise.

Empath: Have already tried different cables (regular 1/4 inch guitar cables): same problem. Have tried moving the cables - trying to get them away from anything else - same problem. I don't have a mixer...

Remember: if i just setup MBP with firewire to 410, cables to monitors: there is no noise, none at all - no problem. The problem only starts if / when I connect a mini display port, or USB, or both.

I have a strong instinct that it's some sort of grounding problem (although not 'ground hum'): the thing that strikes me the most is that the sound instantly and completely disappears if you 'cut the ground' on the power to the speakers (by only plugging in live and neutral, not earth). Sadly I know nothing about electronics though...
posted by Hartham's Hugging Robots at 1:28 PM on October 21, 2010

Is everything plugged in the same power bar? I'd try that if it's not the case.

Can you test it with, say, a TV with an audio aux in, or some sort of home stereo?

It really does seem like a power-related problem, I agree.
posted by Monday, stony Monday at 2:16 PM on October 21, 2010

AC line interference filter. Google it up. For whatever reason your computer is just feeding signal noise into your power source. The filter should totally cancel that. I'm looking at mine right now and it works beautifully.

(Don't mean to sound like a dick...it's just that Google US only brings up 120v versions)

Good luck!
posted by snsranch at 5:50 PM on October 21, 2010

Response by poster: Monday, stony Monday: yes, everything's plugged into the same power bar (I tried that already too!).

It's a good idea to try routing the audio into something else - I'll see if I can find something.

snsranch: thanks for the tip, I'm looking into that now - but one question: where would I put this thing? Between what and what? Also, further to what you were saying - it's seeming surprisingly hard to find a UK version of this. I wonder if they are... somehow inherently related to the US power system?
posted by Hartham's Hugging Robots at 3:39 AM on October 22, 2010

I'd use it to power and isolate your music gear from your computer. You can probably plug a power strip into it if you have multiple components. US power system? That's a great question and I have no idea. I'll look around though and see what I can find.
posted by snsranch at 8:32 AM on October 22, 2010

Ok, I learned a couple of things. RFI and EMI filtering is called mains conditioning in your neck of the woods and there are a couple of ways to do it. Here is one and here is another. The shielded and filtered power strip is a no brainer and I think the ferrite sheilds go on the power supply cord to your computer. I've never tried the ferrite, but they look inexpensive enough to experiment with.
posted by snsranch at 10:00 AM on October 22, 2010

Response by poster: OK, it's a few weeks later, but I wanted to follow this up in case anyone else came by this post with a similar problem.

I *have*, amazingly, arrived at a near solution. I haven't managed to entirely get rid of the screechy noise, but I have managed to reduce by, probably, 80% - 90%, which I think - I hope - is going to be liveable with.

So here's what I did...

I really did appreciate the help above - thanks y'all - but in spite of not really knowing electronics, I just didn't feel entirely confident that the comments relating to in some way altering / filtering the mains power that were being suggested would do it. Real clinchers for me not being confident on this were i) the headphone output being totally clean (therefore if that's clean, why would changing the mains alone change another of the outputs?) and ii) cutting the earth on the monitors instantly providing a total and perfect solution. So I kept investigating. (I had to - the sound was driving me nuts, and I just couldn't bring myself to spending hundreds of pounds on a new something that I really didn't need).

I went back to this http://www.m-audio.com/index.php?do=support.faq&ID=12cfebbf1c694ee8664859cfd004577c, which I'd seen in the early days of investigating. It described the same situation with the headphone output being oddly clear. I tried all the solutions, none worked; so I ended up at the last section of that link, where it said (in effect): if all else fails, contact the manufacturers of your monitors and asking them if you can lift the ground.

I put that off originally because I thought man, they're never going to say that (according to what I read elsewhere, unless it's pretty special equipment, it's very dangerous to do). But in desperation: I did ring them (e.g, Fostex). I eventually got through to a really, really helpful guy, who knew all about electrical engineering - at last :) He said: don't cut the ground on the monitors, it really is dangerous. He said: your ground lifts in the audio signal won't work, because of XYZ technical thing I didn't understand (something to do with the fact that my monitors don't do 'real' balancing; they do artificial eletronic balancing of some kind).

He said: buy one of these, that'll do it. He clearly knew exactly what he was talking about. One of these was... http://cpc.farnell.com/1/1/55112-ground-loop-isolator-a-1095.html. As it happened, I instead bought http://www.maplin.co.uk/Module.aspx?ModuleNo=33172, simply because I could go and physically pick it up ASAP. I figured it would be the same.

He was right - it solved the problem... well, at least, like I said at the beginning, 80 - 90%. To a level where I think it's totally liveable with. (I have a feeling that getting a better solution would entail spending serious money on e.g. some v. expensive 'properly' balanced monitors). I had to buy a whole stack of 1/4in jack > phono converters and various bits and pieces of other cables and converters in order to insert it between the sound card and the monitor... but, simply... it worked. And it was cheap.

So there we go: if you happen to have this problem, and you come across this - because it drove me so mad, I'd like to think I can save someone else this grief :)
posted by Hartham's Hugging Robots at 12:32 PM on November 10, 2010