Locating The General Source
Ask the band be quiet. Then, either boost the monitor or the house volume depending on where the buzz is emanating.
Next, mute your channels one-by-one. Dealing with a house loudspeaker buzz, you should be able to find the offending channel if it is a channel-specific problem.
Dealing with monitor-specific buzz, make sure your channel aux sends are set to post-fader so when you mute the channel, you are also muting the monitor aux send.
Finding The Specific Source
Let’s pick on the ‘lectric guitar because they have the most gear on the stage.
Going through the process I just outlined, let’s say when you mute the electric guitarist’s channel that the buzz goes away.
Looking at the signal path from the guitar to the mixer, you have*:
—The electric guitar
—The guitar’s output cable
—The effects pedals or single-unit effects box
—The associated cables with the pedals/the cable coming out of the processing units
—The direct box for turning that unbalanced cable into a balanced cable for the long run to the sound booth
—The cable from the direct box into the stage jack
—The stage jack cabling either into a snake or directly to the sound booth
*The above can be more complex if they run through an amplifier on the stage. Make a note if they do and adjust your definition of their signal path accordingly.
Start with the area that’s most likely to cause the buzz; the cable into the electric guitar.
Ask the guitarist to unplug that cable and plug it back in. Often, it wasn’t fully plugged in and this will solve the problem.
Next, ask them to plug their guitar directly into the direct box. You will be bypassing their added equipment and will quickly find out if the buzz is or isn’t from their processing units.
If the buzz goes away, ask them to re-seat all the plugs in their pedals and try again.
If the buzz didn’t go away when they plugged into the DI box then have them flip the ground-lift switch. If the buzz goes away, you know it was a grounding issue either caused by ground loop hum or an instrument grounding problem which you can later investigate.
Let’s say the link from the guitar to the direct box still produces buzz in the line. Swap the guitar cable for another one.
Still a problem? Swap the cable from the DI to the stage jack.
Still a problem? Oh, such is the life of a sound tech! Swap direct boxes.
Whenever you have buzz that’s coming from a particular channel, you have two possibilities; anything coming into that channel or, the channel itself. You can figure out how to run out all the possibilities on the stage. The key is swapping out gear until you find the source of the problem.
Back in my radio days, one Sunday afternoon, the station was broadcasting a live NFL game for the Indianapolis Colts. We had a cable patch bay for routing the satellite signals to the broadcast booth. I had to completely crank the volume on the broadcasting mixer to get any decent volume from the satellite. Bad cables can produce a variety of results, from no sound to low sound to buzzy sound.