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Sound chip timings with PAL vs. NTSC
Mega Drive/Genesis systems have different oscillators depending on the region the hardware was manufactured for. The clocks for the sound chips are derived from the oscillator by dividing the master clock by some factor. This means that clocks for the sound chips differ by the manufactured region.
| System | Oscillator (Ø) |
Motorola 68000 & YM2612 ( Ø/7) |
Z80 & PSG (Ø/15) |
|---|---|---|---|
| PAL | 53.203424 MHz | 7.60048914 MHz | 3.54689493 MHz |
| NTSC | 53.693175 MHz | 7.67045357 MHz | 3.57954500 MHz |
Because the sound chips run at different clock speeds depending on the oscillator used, two distinct frequency and tone tables are used for each system region. The interface will automatically detect the machine's region and use the correct respective table.
If you have modified your Mega Drive or Genesis to be able to run at both 50 and 60 Hz modes without also replacing the master clock oscillator, the tunings will not be correct. Ensure you configure your console to use the default video frequency for the region the machine was manufactured for.