A sound's frequency is determined by the value
        stored here.  The lowest value you should use is
        124, since this is about as fast as the Amiga can
        go.  The highest value is 65535.  NOTE:  You MAY use
        lower values than 124 on multisync modes.

How you determine the period depends on how you get your waveform data. If you use a digitizer and the frequency is in Samples-per-second, use this equation: 3579546 AUDxPER = -------------------- Samples-per-second
If you have a group of data that you want played as an "instrument", use this: 3579546 AUDxPER = ------------------------------------- Bytes-Length * Frequency to be played
Of course, the frequency for a given note may be calculated by the old standby: Frequency = Base * 2 ^ (1/12)
Which calculates the frequency for the next note once given a frequency. Middle C comes in at 261.4 Hz.
If you don't want your sound to repeat, you should consider one more thing: when to stop the sound. You see, the faster you play the sound, the faster its going to finish. To figure out how long to let it play, use the following equation: uSec = .279365 * Period * Length Where uSec, is of course, the time in microseconds it takes to play your sound once.
Interesting links: