That is not accurate. On the GZ-70SP (even emulated on MAME) the waveform is correctly Sine. There needs to be a new version that uses the correct waveform.
First there doesn't need to be anything. Second this project is about SW-10, so it's irrelevant what GZ-70SP does differently (even if they use the same ROM).
That is not accurate. On the GZ-70SP (even emulated on MAME) the waveform is correctly Sine. There needs to be a new version that uses the correct waveform.