line level Mono audio input for led flasher
I would recommend the IC LM3916, which has been designed for this purpose.

It's very easy to use and it's cheap. All you will need is:


the LM3916
a 9v battery (just to keep things simple)
the LEDs
two resistors (to set the LEDs current, and sensibility of the circuit).


For an example circuit take a look at the datasheet at page 2, you can also find there the equations to specify the resistors.

If you want to diferentiate between tones, like a bass or a high pitch, you can build copies of the circuit and put a filter in the input of each one. But start with the simpler circuit.

Now go and get a breadboard and start prototyping :)