buzz in mixer weirdness

[jesushimself]

heres the issue
i have my pc hooked into channels 3 and 4 on my mixer, i have my sound module (qsr) hooked into channels 5 and 6. when i turn down the faders on 5 and 6, then 3 and 4 buzz and vice versa . but heres the weirdness...when i have both faders up the buzz goes away, what excatly is causing this cancellation?

 

[jtienhaara]

The buzz is probably still there with the levels up, it's just less noticeable.

There are tons of possible noise sources but the 2 easy ones to sort out are:

- CRT monitors / TVs / anything with cathode ray tubes: keep your cables away from these, they'll give you electromagnetic interference (EMI) every time.

- Light dimmers: Light switches are great, but light dimmers cause a huge amount of noise. If you have one of those sexy black living room lamps from Ikea with a dimmer switch anywhere in your studio then get rid of it!

A common but more difficult problem if you're using unbalanced cables is ground hum. If you have any software that can measure the frequency of a signal, try running the noise (with the faders turned down) through that software. Hum will always be close to 60 Hz.

If it is ground hum, your best option is to use balanced cables. Whereas unbalanced cables carry 2 signals ("hot" and a zero "ground" reference point), balanced cables carry 3 signals ("hot", "cold", and "ground"). Hot and cold are 180 degrees out of phase -- that is, their voltages are opposite. For example, hot might be -0.3 V and cold +0.3 V, at any given instant. A device with a balanced input then "subtracts" the voltages, using a transformer or an op amp, in order to arrive at the signal amplitude: 0.6 V.

This approach eliminates the need for a reference "ground" signal, and so eliminates ground hum.

Depending on the gear you're connecting, you may or may not be able to connect balanced cables. You'll have to check the specs of the gear you're using to see whether the ins + outs are "balanced" or "unbalanced".

Oh, and one last note -- you might be better off using Mute buttons for the short term.

I hope this helps Jesushimself! Cheers,

Johann

 

[jesushimself]

yeah, ground hum seems like the answer, ive run everything on its own iondependent circuit, i have an maudio audiophile usb sound card, the outputs are unbalanced. the buzz is real low with the levels jacked up, the only real problem i see is will it record? am i going to hear this buzz while recording, ive ran some tests and i dont hear any buzz, is it there though?
what programs would you recommend for measuring the frequency?

thanks
jesus himself

 

[jtienhaara]

Hi Jesus Himself.

Whatever you hear as you're recording / mixing will be what you get in the final product. There is no magic there.

If you want a cheap "cheat" then you can put a software gate or expander on each your input signals. However this will affect the sound of the signal...!

Shorter cables will also help. Better cables will help (lower AWG = thicker wire = better; also higher shielding = better). A power conditioner for all your audio gear might help, although personally I think there's a bit too much "physics voodoo" in power conditioners.

As to frequency analyzers -- I'm afraid I don't know of any offhand, but I'm sure they exist.

(I use the CreamWare platform, and so the analyzers available to me are DSP-based.)

Incidentally there will always be a noise floor. If yours isn't detectable it might even be safe to ignore it. A noise floor at -75 dbFS or so will generally be well below what anyone can hear.

Sorry I can't be of more help! I do hope you resolve your noise issues!

Cheers,

Johann

 

[jesushimself]

youve been of great help, dont be so hard on yourself, im almost sure it is some type of floor noise, its highly understated. the only time it rears its head is when all levels are maxed.
i do have a power conditioner and i couldnt agree more with yr theory on "physics voodoo". there really is no avoiding some noise, be it the faintest.

thanks
jh