The amplitude of the sounds you play is determined in code. Units of the sound data sent to the loadSound() method of the AudioPlayer class are volts (not normalized) so the vector [.1 .5 -1 2] will play four samples at the current sampling rate, of 100mV, 500mV, -1V and 2V respectively. Standard line-level audio signals range between -1.4 and 1.4V. Depending on your audio amplifier, you may be able to safely scale your sound data to +/-2V without saturation.
I hope this helps,