In SX Microcontrollers, SX/B Compiler and SX-Key Tool, George Herzog wrote:

Microphones are microvoltage analog sensors, so they need a preamp to have enough power to be sensed by microprocessor.  Electret mics are cheap, but also need to be provided with DC power.  Google for info.

You have several choices: use an OpAmp, use an Audio Amp or PreAmp chip, or use a transistor or two.  Much depends on your own preferences and how much hassle you want in terms of design.  The big plus with a single supply OpAmp or AudioAmp chip [I think there is an LM358 Audio Amp that will output .20 watts when run from 5Volts - it prefers 9, but works.] is that you have good audio properties with a simple power supply.  Discrete component amplifiers often have stages which require progressively higher supply voltages and maybe dual voltage supplies.  There are tons of audio schematics on the internet.

Once you get the audio powered, then you have to figure out how to use it.  The frequency is the easiest to sense.  Alternatively, you might want to sense amplitude as well as frequency.  The latter might be best tackled with a ladder of resistors feeding 4 or 8 pins.  As the amplitude increases, more pins go high.  You just read the whole nibble or byte and then you have both tempo and amplitude to manipulate and distribute to whatever.  With the resistors, you might want to power that audio chip from 9 volts as you are going to have a voltage drop and you need at least 2.5volt to indicate a digital high pin.  What to do is to clip the overvoltage with a 5.1 volt .5 watt zener.   In that way you can include a volume control to find a 'sweet spot' where you get the best response with whatever you have built.

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