Basically correct, except I wouldn't use a schmidt trigger because you can make a schmidt trigger out of an op-amp, but you can't make an audio amplifier (gain stage) out of a schmidt trigger. The bandpass filter can be done by sizing capacitors on the gain stage, so it doesn't need to be a seperate building block. The peak detector goes to the "fake" schmidt trigger, and viola...3 op-amps in a single package will get you where you want to go. (Get a quad op-amp, there's always a use for the spare.)