My first guess would be the compressor is causing it. Perhaps your mic is too close to your monitors? Maybe if you lifted all your cables off the floor it would decrease or go away? These are the first things I would check.

It's the computer.

Time to go down the troubleshooting sequence.

1. The MBox has a preamp. How does the mic sound through that (no blue tube, no compressor)

2. Next put the Bluetube back. Hum? My money is on bad gain structure here. (With so little info we are all guessing.)

3. Next try the compressor. Could be it. Again, gain structure is the key.

It's the compressor.

BobRogers wrote: Time to go down the troubleshooting sequence.

1. The MBox has a preamp. How does the mic sound through that (no blue tube, no compressor)

2. Next put the Bluetube back. Hum? My money is on bad gain structure here. (With so little info we are all guessing.)

3. Next try the compressor. Could be it. Again, gain structure is the key.

thanks for the response. I have the mbox's gain completely off, i first pull up the gain on my bluetube and then use the make up gain on the compressor. what exactly do you mean by bad gain structure??

Bad gain structure is all about creating hiss and hum from otherwise perfectly working equipment. An example of which is what you're doing... Assuming your equipment isn't faulty. Which only you can figure out by doing what Bob suggested.
Have a nice day.

Agree on computor/monitor. Both can be source of MAJOR electro noise. Whines, buzz and such. Usually decreases as you move away...

Process of elimination...

Whenever you have several amps in series (as you do) you have lots of ways to adjust the knobs to get the same net gain at the end. You want to do this in a way to get the maximum headroom between the noise floor and clipping. Search the web and this site for more info - it's worth a long explanation.

The computer/monitor interference possibility that others have talked about is also a good idea. But you still need to read up on gain structure.

Gain structure rules!

It's the cables.

I defer to my signature here...

*reads from sig*

-Ben(t)

Informative. Now what has that got to do with anything :) ?

But yes, it does. I can't begin to understand how friggin easy it is to do the sound now that I set the gain properly (properly still being -10dB off) It is so much easier to mix.

...And there you have it!

the noise is deff comming from my compressor, and i cant figure out why. my mic directly to the mbox is clean. the mic into my preamp then to mbox is clean. when the compressor gets put into the chain is where the hum is comming from.....

let me know whats wrong in my gain structure please!!! :D

1. mic into blue tube pre (preamp gain set at about 9oclock, aprox 1/4 the way up usually gets me a hot enough signal)

2. pre amp to compressor(dbx 266XL)(connecting using a xlr/xlr cable) usually using the auto settings and gating so theres about 3db reduction.

3. compressor to mbox( connecting using an xlr-1/4 inch cable)
gain is all the way off on the mbox as though it should be?

any thoughts???

ps. I've also been told that when I make the final connection from the compressor to the mbox i should be using the line switch and not the mic switch(this will bypass the pre in the mbox and only use the blue tube......yet for some reason i cant even get a signal when its set to line, i am forced to use the mic setting even though im using the line jack...could this be the issue?

Yep, it's the compressor.

Maybe too much make up gain on the compressor? Set the compressor to 1:1 with no make up gain to check it out.

Or the power supply to the compressor? Is everything coming out of the same wall outlet in a power strip? I get a buzz with some of my gear If I'm not careful, and sometimes it isn't at 60Hz.