The base of a trasistor is its input. A current-limiting resistor must be used in series with the base so that the music source and the transistor don't blow up. Then if the music is more than 0.7V the transistor will turn on briefly for half the music. The other half of the music will blow up the transistor if a reverse diode isn't across its base-emitter. A resistor should also be across the base-emitter to turn off the transistor when it shouldn't be turned on.
So a transistor, three resistors, a diode and an LED will work, but poorly.
I have a circuit that quickly charges a capacitor to the peak level of music and the capacitor holds the peak for a few moments that are long enough for your eyes to see. The LM386 can drive up to 18 LEDs each one with its own current-limiting resistor.
I have a Veroboard layout for it if you want.