At a band soundcheck the other week, I tried to put my dynamic mic into my guitar effects unit, a Boss ME8, then into the desk for the PA. The sound engineer inserted a DI box after the Boss unit, but said the level was too low. He said the DI box only brings a level down, and won't bring it up to produce a stronger signal. I thought what DI boxes do is increase a low signal to a high signal. Who's right?
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Technical Editor Hugh Robjohns replies: I'm afraid that the sound engineer was right! DI boxes are designed to take an unbalanced low- to medium-level, high-impedance signal from a guitar or similar and convert it to a mic-level, balanced and low-impedance signal intended for connection to a sound desk microphone input. Most DI boxes also have an earth-lift facility to help break ground loops, and many have facilities to accept line-level and speaker-level inputs and reduce them to mic level as well. Not even the active DI boxes provide gain.