Grumpy_Mike:
The main problem is that a sound like a clap is a complex waveform and is not just one frequency. That makes it difficult to recognise.
For getting at the frequency content of a waveform look to use a FFT. However that gives you in effect a list of all the frequencies and their relitave strengths. Recognising a specific sound is a lot more complex because its FFT will change over time.
While you can implement a band pass filter digitally it will not be a very high order filter due to the lack of processing power of the arduino.
I understand they are complex frequency but everything has a fundamental or a dominant freq, so you can basically search for a specific freq something likes to resonate at. I have done this purely digitally, no problem. It's doing it with an arduino that I am stuck on.