APU Note Mode (alternative version of #334)

[JerwuQu]

This is another go at #333, but with a slightly different approach from #334.

Big thanks to @marler8997 for the detailed proposal and the other PR!

Has been tested working on both web and native.

Reasoning

Since frequencies sent to tone are integers, we lose quite a bit of precision when it comes to playing lower notes. This PR implements a variant of #333 to make tone capable of playing MIDI notes. We have 16 bits per frequency, which is split up into 8 bits for the note, and 8 bits for optional pitch bend, as to not be limited to pure notes.

It turns out the implementation for this is very simple (JS implementation required less than 15 lines!), and since the flag is new and optional it doesn't affect any prior carts. In my opinion this feature is overdue.

Usage

Instead of calling tone with frequencies, you supply it with notes. The list of MIDI notes is easily googlable and easier to use than frequencies: https://inspiredacoustics.com/en/MIDI_note_numbers_and_center_frequencies

// Play A4 (440Hz)
tone(69, 0, 0, TONE_NOTE_MODE)
// Play A4 bent halfway up to the next note (A#4)
tone(69 | 128 << 8, 0, 0, TONE_NOTE_MODE)

One could compare the pitch bends to cents between semitones in music, where 128 bend would be the equivalent to 50 cents.

Compared to #334 in short:

• TONE_NOTE_MODE flag for tone rather than a system flag.
• Puts the main note in the lower bits rather than the upper bits (i.e. tone(note | bend << 8, ...) rather than tone(bend | note << 8, ...).)

[marler8997]

Modifications to my original proposal seem fine to me, Id be happy with this or the original.

[aduros]

This feels really clean, I like the small adjustments over the other PR 🙂

Could you also add a short tip somewhere to the doc page here? https://wasm4.org/docs/guides/audio

[JerwuQu]

A broken link and accidentally rebasing onto the wrong branch later and it should be ready for review again :)