Once created, can ToneGenerator's volume be changed?

Question

I need to replay a single tone repeatedly with the volume reducing until it is quiet.

I'm creating a ToneGenerator object with:

ToneGenerator toneGenerator;
toneGenerator = new ToneGenerator( AudioManager.STREAM_MUSIC, 100);

But, I have not found a way for the ToneGenerator to change the volume after it's been created.

Is this possible, or should I look at another way of reducing the volume?

EDIT: I'm restricted to using API 19 and lower.