AudioExplorer functions as a simple audio recorder/playback application.  It can record from any audio device attached to your computer, and it can read WAV or MP3 format files for playback through any attached audio device.
Audio samples - either recorded or played back - are fed into a Spectrum Analyzer.

The Spectrum Analyzer generates lists of frequencies and corresponding signal strengths.  These may be viewed directly as a needle-plot, or in a more musical form as notes on a piano keyboard.
In real-time operation, a Note Processor performs optional filtering - e.g., attempting to discern overtones, merging shoulders of very strong signals, and monitoring the overall dynamics of the incoming signals and adapting accordingly.
The Midi Assembler integrates the information coming out of the Note Processor and makes the final decisions about what changes in any given note signal constitute a MIDI event.
In batch operation, a series of frequency spectra can be saved to disk for subsequent detailed analysis, and/or converted into a Frequency Map, which is a very high resolution map of the signal intensity of each pitch over the duration of the recording.

Alternatively, the frequency data can be distilled into a NoteMap, an image with similarly high resolution but which can be generated dynamically in response to various optional settings. When the NoteMap optimally configured, it can be used to generate a standard MIDI file.