Alesis 12R manual Avoiding noise, System noise ground loops, hum, induced noise

Operating Instructions

Avoiding noise

If the Multimix 12R is being run as suggested above, the noise of the mixer itself will not be a significant factor in the noise level of your system, since the Multimix 12R generates much less noise than the typical source does. Noise is present in every system, analog or digital; as operator it's your job to run the system (and particularly the mixer) so that the noise isn't amplified unnecessarily. But the Multimix 12R cannot remove noise that is already there. If a low-level source with a poor signal-to-noise ratio is amplified by the TRIM and channel fader, the noise will be amplified with the desired signal. A system is no quieter than its noisiest component.

System noise (ground loops, hum, induced noise)

In today’s studio, with dozens of different pieces of equipment and computers, there are many opportunities for ground loop problems to occur. These show up as hums, buzzes or sometimes radio reception and can occur if a piece of equipment “sees” two or more different paths to ground, with one of the paths going down a signal line. While there are methods that can virtually eliminate ground loops and stray radio frequency interference, such as installing a separate power source just for the sound system, most problems are easier to solve. Here are some basic techniques that you should use to keep stray hums and buzzes to a minimum.

❿KEEP ALL ELECTRONICS OF THE SOUND SYSTEM ON THE SAME AC ELECTRICAL CIRCUIT. Most 60-cycle hums happen because different components of a sound system are plugged into outlets of different AC circuits. If any noise-generating devices such as air conditioners, refrigerators, neon lights, etc., are already plugged into one of these circuits, you then have a perfect condition for stray buzzes as well. Since most electronic devices of a sound system don’t require very much power (except for power amplifiers), it’s usually safe to run a multi-outlet box or two from a SINGLE wall outlet and plug in all of the components of your system there.

❡KEEP AUDIO WIRING AS FAR AWAY FROM AC WIRING AS POSSIBLE. Many hums come from audio cabling being too near AC wiring or the power transformers ("wall warts") used by equipment requiring an external supply. If a hum occurs, try moving the audio wiring around to see if the hum ceases or diminishes. If it’s not possible to separate the audio and AC wiring, make sure that the audio wires don’t run parallel to any AC wire (they should only cross at right angles, if possible).

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