Note synthesis

Synthesizes PCM from SpeakerNote sequences. More...

Data Structures
struct	NoteSequenceState
	Playback state of a note sequence. More...

Functions
void	note_seq_init (NoteSequenceState *s, const SpeakerNote *notes, uint32_t count, uint32_t sample_rate)
	Initialize a note sequence player.
uint32_t	note_seq_fill (NoteSequenceState *s, int16_t *out, uint32_t max_samples)
	Fill an output buffer with synthesized PCM samples.
void	note_seq_deinit (NoteSequenceState *s)
	Clean up note sequence state.
uint32_t	note_phase_inc (uint8_t midi_note, uint32_t sample_rate)
	Compute the per-sample phase increment of a MIDI note.
int16_t	note_synth_sample (uint8_t waveform, uint32_t phase_acc, uint32_t phase_inc, uint8_t velocity)
	Synthesize one PCM sample of a waveform.
uint32_t	note_midi_freq_x256 (uint8_t midi_note)
	Get the frequency of a MIDI note.

Detailed Description

Synthesizes PCM from SpeakerNote sequences.

Also provides the waveform primitives the track player uses for its voices. These are kernel internals, not part of the app SDK.

---

Data Structure Documentation

NoteSequenceState

struct NoteSequenceState

Playback state of a note sequence.

Data Fields
bool	active	Whether notes remain to be played.
uint32_t	current_note	Index of the note being played.
uint8_t	current_velocity	Velocity of the current note.
uint8_t	current_waveform	Waveform of the current note, a SpeakerWaveform.
const SpeakerNote *	notes	Notes being played, not owned.
uint32_t	num_notes	Number of entries in notes.
uint32_t	phase_acc	16.16 fixed-point phase accumulator.
uint32_t	phase_inc	Per-sample phase increment, 0 for a rest.
uint32_t	samples_remaining	Samples left in the current note.

Function Documentation

note_midi_freq_x256()

uint32_t note_midi_freq_x256

(

uint8_t

midi_note

)

Get the frequency of a MIDI note.

Used by the track player to compute sample playback pitch ratios.

Parameters

midi_note

MIDI note number.

Returns

Frequency in 16.8 fixed-point Hz (i.e. Hz * 256), 0 if out of range.

note_phase_inc()

uint32_t note_phase_inc	(	uint8_t	midi_note,
		uint32_t	sample_rate
	)

Compute the per-sample phase increment of a MIDI note.

Parameters

midi_note	MIDI note number.
sample_rate	Output sample rate in Hz.

Returns

16.16 fixed-point phase increment per output sample, 0 for a rest (note 0) or out-of-range values.

note_seq_deinit()

void note_seq_deinit

(

NoteSequenceState *

s

)

Clean up note sequence state.

Parameters

s	State to clear.

note_seq_fill()

uint32_t note_seq_fill	(	NoteSequenceState *	s,
		int16_t *	out,
		uint32_t	max_samples
	)

Fill an output buffer with synthesized PCM samples.

Parameters

	s	Note sequence state.
[out]	out	Output buffer for signed 16-bit PCM samples.
	max_samples	Maximum number of samples to generate.

Returns

Number of samples written, 0 once the sequence is done.

note_seq_init()

void note_seq_init	(	NoteSequenceState *	s,
		const SpeakerNote *	notes,
		uint32_t	count,
		uint32_t	sample_rate
	)

Initialize a note sequence player.

The sample rate is kept in a single global, so all sequences played at once must share it.

Parameters

[out]	s	State to initialize.
	notes	Notes to play. Must stay valid until playback ends.
	count	Number of entries in notes.
	sample_rate	Output sample rate in Hz (e.g. 16000).

note_synth_sample()

int16_t note_synth_sample	(	uint8_t	waveform,
		uint32_t	phase_acc,
		uint32_t	phase_inc,
		uint8_t	velocity
	)

Synthesize one PCM sample of a waveform.

Waveforms are normalized to roughly equal loudness. The square wave applies PolyBLEP anti-aliasing at its discontinuities, using phase_inc.

Parameters

waveform	SpeakerWaveform value; unknown values produce silence.
phase_acc	16.16 fixed-point phase accumulator.
phase_inc	Per-sample increment of phase_acc.
velocity	Amplitude scale, 1 to 127; 0 means no per-sample scaling (master volume is applied downstream).

Returns

Signed 16-bit sample.