David's Tip of the Day: Amp Tremolo with Harmonica
Students walk in with amps that have tremolo and they ask, "what's that do?" and I commonly say, "we don't use it" and move on to the tone controls. It IS used sometimes. Listen to Little Walter's 1960 release "Going Down Slow" where uses amp tremolo (the copy I have is from the "Blues With A Feelin'" release).
To loosely define amp tremolo... it's an effect that takes what you play and quickly fluctuates it in volume... similar to how we do it in the throat, where our vocal chords open and close in a rhythmic fashion to create what we call a throat tremolo.
You can choose how fast the tremolo goes on the effect, just like we can with our throat tremolo (the downside is the amp tremolo is always on, where we commonly choose to place throat tremolo only on longer notes).
Though we don't commonly use the amp tremolo, it can be cool once and a while. I remember a conversation with Piazza where he stated that he was listening to Little Walter's recordings and that he noticed Walter using amp tremolo more than he previously thought.
P.S., if you use amp tremolo, turn off your throat tremolo :-)