Load or extract local sound

I need to change the pitch of a local library sound rather than a URL. Here is part of Andre Michelle’s code which does it for a URL. (extraneous code missing)

function playString( myString: String )
{
_target = new ByteArray();
SoundMixer.stopAll();
pitchSound = new Sound();
pitchSound.addEventListener( Event.COMPLETE, complete );
pitchSound.load( new URLRequest(myString) );
_position = 0.0;
_sound = new Sound();
_sound.addEventListener( SampleDataEvent.SAMPLE_DATA, sampleData );
}
//more code
function sampleData( event: SampleDataEvent ):void
{
var read:int = pitchSound.extract(_target,need,positionInt);
}