Hah I never noticed that those were those notes! I believe that's just a remarkable coincidence because the first, lower note is just the result of the SN76489

Hah I never noticed that those were those notes! I believe that's just a remarkable coincidence because the first, lower note is just the result of the SN76489 sound chip being powered up but "uninitialised", as it were. In theory different chips would give different tones but in practice all the ones they used seemed to give a consistent result.