keyboard scales coding

[enorrmann]

I found

#define NOTES_IONIAN 2741
#define NOTES_AEOLIAN 1453
#define NOTES_PHRYGIAN_DOMINANT 1459
#define NOTES_MINOR_BLUES 1257

I'm trying to explore other modes, in particular chromatic
how are those values encoded ?

[enorrmann]

I suspect this
They use a 12-bit binary mask pattern, where each bit represents one of the 12 semitones in an octave (bit 0 = C, bit 1 = C♯, …, bit 11 = B).
Bits set to 1 indicate which notes belong to the scale; the integer value (e.g., 2741) is just that 12-bit mask in decimal form.

[bangcorrupt]

Yes, it's a bitmask, LSB is the scale root and is always set. See Ian Ring's website for all the scales. I used a 32 bit mask so we can hopefully support micro-tunings later, but I only tested with 12 tone scales.

In t_scale, notes is the bitmask of note positions, and tones is the number of tones in the tuning system (i.e. 12 tone equal temperament). In t_keyboard, split is the difference between the 2 rows of pads and repeat is the number of degrees in the scale (set automatically when the keyboard map is generated).

For a chromatic scale:

// 12 bits set.
#define NOTES_CHROMATIC 4095

static t_keyboard g_kbd;
static t_scale g_scale;

scale_init(&g_scale, NOTES_CHROMATIC, 12);
keyboard_init(&g_kbd, &g_scale);

// 12 notes in a scale will overflow the bottom row of pads,
// so we need to reduce the value of `split`, I think to 8.

keyboard_set_split(g_kbd, 8);

...

// Then we can get the MIDI note number from the trigger pad number.

note = keyboard_map_note(&g_kbd, pad);

// And transpose as an offset from C.

note += 5; // Transpose to F.

...

I didn't get as far as implementing mode rotation, t_scale has a member for it but it isn't used. Currently we call keyboard_map_note every time a trigger pad is pressed. If we pre-compute a lookup-table instead, we can probably implement mode rotation as a pointer offset.

The scale and keyboard mapping code probably has plenty of bugs, I wrote it quickly and haven't looked at it for a long time.