USB keyboard making weird noise in speakers

[marcnyc]

I was wondering if somebody has any ideas on how to troubleshoot this...
I have a USB Midi music keyboard by Edirol connected to my Mac Book Pro via USB only (no other cables involved) through a USB hub. I have some speakers connected to the output of my Mac. Anytime the USB cable from the keyboard is connected into the hub there is a hum in the speakers... it drives me crazy so I disconnect the keyboard but it would be nice to leave it plugged in and yet I don't see how a USB connection can crearte a hum... any ideas?

[DeltaMac]

So, your MIDI keyboard creates a ground loop when connected to the USB hub?

Do you also get that hum when you connect the MIDI keyboard directly to your MBPro? (bypassing the external hub)?
Have you tried some of the simple tricks, such as reversing AC connections (if possible)?

Some USB hubs do _not_ behave very well with audio devices. Is your USB hub self-powered (with its own power supply), or bus-powered (powered through the USB cables only). If self-powered, try disconnecting the external power supply, to see if all your devices continue to work (some may need that powered hub, but you may be fine with everything)

[marcnyc]

Thanks for your suggestions DeltaMac.

The hum goes away if plug directly into the MBP however I cannot work like that because I only have 2 USB ports... one is in use by the Apple Cinema Display and the other one has the hub on to power all my USB devices.

The USB hub is powered. I did try unplugging the power and the hum actually got a bit louder. I know I need the power to the hub when all of my devices are on.
I did try reversing AC connections, no change.

[DeltaMac]

Did you simply switch AC connections, or did you actually flip the power plug (not always possible)? You should flip only one plug at a time, so you can check for any affect.
Also, if possible, try connecting the AC power for your _keyboard_ to a different AC circuit. That would be one controlled by a different circuit breaker.

If I were there to help, I would pull out my AC circuit tester, and make sure that all your AC outlets, including any power strips/surge suppressors are properly wired and grounded correctly. One like this works great for that: http://en.wikipedia.org/wiki/Receptacle_tester

If none of this helps, you might consider replacing your USB hub with one that is more audio-friendly.

[marcnyc]

I have flipped the power adapter of the USB hub but it's the only one that can be flipped as it goes into a power strip that has a 3 prong...

What is an audio-friendly hub?

[DeltaMac]

There are some USB hubs that have an audio pass-through, but that's not really the solution. Some are advertised as having quality components, with low noise as a goal. You could try another brand (or two) to see if that helps. You might be able to borrow one, just to try.
Found this (for a laugh) http://www.thinkgeek.com/product/eec...c=5&zmap=CEECF
Here's one that I suggest as a possible fix (assuming that you discover that your USB hub is the issue (and not just passing along a faulty connection)
http://www.amazon.com/D-Link-DUB-H4-...ef=pd_sbs_op_5

[marcnyc]

i would need at least 5 ports... is there a 7 port you might suggest?

[DeltaMac]

I think you need to check the links that I provided, the first is a 28-port USB hub.
That's a few more than 5, eh?
And, D-Link certainly sells a 7-port.
Same style here: http://www.amazon.com/D-Link-DUB-H7-...eywords=DUB-h7
Want more ports? this one appears to have good reviews: http://www.amazon.com/Plugable-USB-P...ywords=usb+hub

[marcnyc]

well you said yourself that the first link was just for laughs ;-)
I just don't understand how these hubs would be different than the one I have, but I will give one of them a try and see if they really are

[DeltaMac]

Ah - since I have started working on computers, a few years before USB even existed, I have seen more problems caused by faulty USB hubs, than almost any other device (with the exception of external hard drives). They are just not that expensive to replace, and often - everything you add to your computer goes through that hub. So, lots of "availability" for problems with that, or they most often fail because of age. I see brand new Macs with 8 or 10 year old USB hubs still in use.

That's why I also suggested that you try to borrow one, if possible, just to test if the problem (hum) changes, or completely disappears with a different hub.
You're picking up a ground loop (that's what causes the hum)
The common item right now, is the hub. So, you should try a different hub to see if that helps. Possibly, it won't help at all, but you won't know until you try.
Another thing you can try is to replace your USB connection cables, particularly the one used with the keyboard.
Be sure to check your AC power outlets, if you haven't done that yet, for proper grounding.
Another tip is to experiment with an _ungrounded_ power cord (use a 2 to 3 wire plug, easy to find where appliances are sold. That allows you to try disconnecting the ground on 3-pin plugs, without permanently damaging the plug.
_Don't_ leave a ground bypassed for longer than to test for a change. The ground connection is there for your safety, but you may be able to pin down which device is causing the ground loop. It takes time, and a lot of experimenting. Sometimes you get lucky....
You might also ask at a local sound/audio specialist for some other tips.

Here's a really different USB hub. You would really need a good purpose for that one, I think: http://vaunix.com/products/high-qual...b/overview.cfm