Real World Digital Audio

Noise and Hum

You’ve probably had the experience of plugging equipment in, turning it

on, and hearing a loud hum. Even digital audio relies on analog voltages,

which means your computer music setup involves lots of electricity. If that

electricity isn’t properly grounded, meaning the audio wiring is properly iso-

lated from the power wiring, electrical interference will be added to your

mix in the form of noise and hum.

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How Ground Loops Happen

Electricity makes digital music possible, but it can be the enemy.The setup pictured in Figure 3.8 is quite likely to pro-

duce a ground loop. Most buildings have just one ground, probably a connection in the basement or crawlspace that

connects the wiring to the earth. Each wall outlet should provide a connection to that ground. This isn’t likely to be a

problem until you plug one piece of gear (like your computer) into one outlet, then plug another piece of gear (like pow-

ered speakers) into a different outlet. At this point, there’s likely to be more resistance in one of the ground connections

than in the other, which will cause a current to flow through the ground loop.When you plug the audio cables between

the speakers and the computer’s audio interface, you create a full loop, and your audio rig may suffer from unwanted hum.

Figure 3.8 This is

one way to create a

ground loop. Any setup

with multiple routes

to ground will have

the same result.

Audio

Power

Power

Ground