For the last few weeks, we've discussed sound system gain structure. We've covered matching signal levels, matching impedance levels, and unity gain. I'm going to push the pause button momentarily in order to help bring clear application to these principles. How can you make sure your system has been set up correctly? Here are the steps.
- First, use a tone or pink noise generator to send a consistent tone through your system. You may want to shut off your amplifiers in the beginning to save your sanity. Some consoles have tone generators on-board, or you can purchase a CD with tones on it and put one of the tracks on repeat. Plug the tone generator into one of the inputs on your mixer. Adjust the gain knob (trim) so that the tone is steadily at 0dB on the output meters of your board.
- Now, step one piece of equipment at a time through the signal chain of your system. Set the output of the first piece and the input of the next at unity gain. Check your output and input meters. They should both register at exactly zero dB. Continue this all the way through to the input of the amplifier.
- If the input of the second piece of equipment is significantly lower than zero dB, you have a gain structure problem that will most likely lead to increased noise. Check to make sure that the levels match, the impedances match, and that you are setting everything at unity gain.
- If the input of the second piece of equipment is significantly higher than zero dB, you have a gain structure problem that will most likely lead to distortion. Again, double-check all the things above to identify where the signal jump is happening.
- Make any necessary changes according to the earlier posts. (Signal matching, impedance matching, unity gain)
- Once everything is matched and set correctly, play your favorite CD through the system and turn the amplifiers up until your system reaches an appropriate level for your church's style of music. The amps may not need to be turned up all the way. This is fine and likely means you will be minimizing noise in the system while maximizing your dynamic range.
- Finally, practice with your singers, band or worship team at least once before the next Sunday. If you find that you are hitting red lights on any equipment, go back and turn the amps up just a little until you are able to turn down the output levels of your mixer so that nothing distorts and you have a little extra headroom left over.
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