Three SN76489 Pulse Channels for Sample Playback

I have updated the code for how my SN76489 USB MIDI plays back samples.

Previously, I would use a single pulse channel and then trigger samples using the volume of that single pulse channel using amplitude sample data.

The aim of using only one pulse channel was that it would free up the other channels for melodic and harmonic use.

However, the result is that the sample playback is very, very soft in volume, meaning that there is more overall unwanted noise, and that there is also a limit to how the other channels can be used velocity-wise in order to balance out the single pulse channel that is used for sample playback.

I have decided to try out using all three pulse channels for sample playback, and all though this limits the use of all pulse channels on that particular SN76489 chip whenever sample data is playing.

The effective outcome is a much more balanced sample function in terms of volume. Samples also seem to sound 'crisper', less gain is needed to bring the chip up to appropriate levels.