Am I reading this all wrong? If it takes a 16 bit value, I thought OCR1A and OCR1B are treated as a single register. Doesn't the ISR, TIMER1_COMPA_vect, only get called when TOV1 reaches MAX? It's in the ISR that I put in the new OCR1A value for the new frequency. For some reason I just can't seem to get the penny to drop on this one when it seems to be a simple thing...change the frequency.