software synthesiser problem.

Hello! I was just wondering if anyone here has made a software synthesiser using direct music. My problem is that whatever tone I play ( unsing the correct frequency ) it always plays a ''g'' but with different amplitude and frequency (octave). If I change my double buffer size it plays with different speeds, the same happens when I change the amount of sleep(x) inside my player thread. This sounds a bit confusing but hopefully someone understands what I mean. Thanks!