Just some notes and links I've amassed on dealing with audio in Java.
Squelch / Sound Detection
DSP / Processing
Radio Signal Analysis
According to Dick Baldwin, the audio sampling frequency should be almost ten times higher than the highest frequency to be deconstructed to a digital signal if the audio is to be reconstructed to an analog signal. If the deconstructed signal is to be analyzed in a purely digital nature, the sampling rate should be at least two times the highest frequency. A quick look at a Midians tone-signalling wall chart will show that the highest frequency commonly used in radio tones is 2175 Hz, used in tone remote applications. Burst tone frequencies can exist as high as 3150 Hz. Plectron tones can go as high as 3478 Hz. Therefore, to accurately deconstruct the audio and capture all paging tones, the sampling rate should ideally be around 2-3 times the highest frequency, or between 8,000-12,000 Hz.