ts::PitchRamp Class Reference

The per-voice pitch ramp that glides the sampler's read rate across a control block. More...

#include <tabulasonora/pitch_ramp.hpp>

Public Member Functions
	PitchRamp (std::span< const std::int32_t > ramp_exp) noexcept
	Creates a ramp over the shared exponential table, which must outlive it.
std::int32_t	increment_of (int value) const noexcept
	The 16.16 sampler increment a domain value decodes to.
void	arm (double from_ratio, double to_ratio) noexcept
	Arms the ramp to glide from one ratio to another across the coming block.
bool	is_active () const noexcept
	Whether the ramp still has ground to cover.
std::int32_t	next_slot () noexcept
	Advances one slot and returns the increment that serves the next eight samples.

Static Public Member Functions
static int	domain_of (double ratio) noexcept
	Converts a playback ratio into the ramp domain.

Static Public Attributes
static constexpr int	samples_per_slot = 8
	Samples one increment serves; the engine writes four of these per 32-sample chunk.
static constexpr int	unity = 0x38000
	The ramp domain's value for unity rate.
static constexpr int	units_per_octave = 0x4000
	Units per octave, and the divisor that puts milli-semitones into them.
static constexpr int	milli_semitone_divisor = 375
static constexpr int	domain_max = 0x3FFFF
	Largest value the exponential decode accepts.

Detailed Description

The per-voice pitch ramp that glides the sampler's read rate across a control block.

The engine does not step a voice's pitch once per 10 ms tick. voice_pitch_block_init records the pitch entering the block at voice+0xb8 and the pitch leaving it at +0xbc, and ramp_env_step_eval then walks between them while the block renders, writing a fresh sampler increment every 8 samples. Without that glide a voice whose pitch moves far inside one block reads its wave from a measurably different place forever after: the sub-sample residue the glide leaves behind is frozen into the sampler's phase, which selects a different interpolator row for the rest of the note. Drum tone 1946 is the case that exposed it — its pitch envelope drops 6.671 semitones inside block 0, the engine gains 1.693481 samples across that block, and the resulting phase of 45448 costs about 1.1 dB and a visibly brighter top octave.

The ramp domain. Both endpoints are formed as 0x38000 + (milli_semitones << 9) / 375, so 0x38000 is unity and one octave is exactly 16384 units — the same octave size g_ramp_exp_tbl uses for the TVF's f, which is why both stages share the table.

Constructor & Destructor Documentation

PitchRamp()

ts::PitchRamp::PitchRamp ( std::span< const std::int32_t > ramp_exp )

inlineexplicitnoexcept

Creates a ramp over the shared exponential table, which must outlive it.

Member Function Documentation

domain_of()

int ts::PitchRamp::domain_of ( double ratio )

inlinestaticnodiscardnoexcept

Converts a playback ratio into the ramp domain.

The engine arrives here from milli-semitones, but the port computes a ratio, and the two agree exactly because the domain is logarithmic with a known octave size.

increment_of()

std::int32_t ts::PitchRamp::increment_of ( int value ) const

inlinenodiscardnoexcept

The 16.16 sampler increment a domain value decodes to.

Transcribed from ramp_env_step_eval: interpolate the table, round toward zero on the negative side, then apply the variable shift that carries the octave.

arm()

void ts::PitchRamp::arm ( double from_ratio, double to_ratio )

inlinenoexcept

Arms the ramp to glide from one ratio to another across the coming block.

The step is ((to - from) * rate) >> 13 exactly as voice_set_ramp_target_0 forms it, with the engine's maximum rate of 0xfff — which makes the ramp cover the interval in two steps, the behaviour measured on every voice examined. A ramp whose endpoints coincide stays inactive, which is the common case and costs nothing.

is_active()

bool ts::PitchRamp::is_active ( ) const

inlinenodiscardnoexcept

Whether the ramp still has ground to cover.

next_slot()

std::int32_t ts::PitchRamp::next_slot ( )

inlinenodiscardnoexcept

Advances one slot and returns the increment that serves the next eight samples.

Member Data Documentation

samples_per_slot

int ts::PitchRamp::samples_per_slot = 8

staticconstexpr

Samples one increment serves; the engine writes four of these per 32-sample chunk.

unity

int ts::PitchRamp::unity = 0x38000

staticconstexpr

The ramp domain's value for unity rate.

units_per_octave

int ts::PitchRamp::units_per_octave = 0x4000

staticconstexpr

Units per octave, and the divisor that puts milli-semitones into them.

milli_semitone_divisor

int ts::PitchRamp::milli_semitone_divisor = 375

staticconstexpr

domain_max

int ts::PitchRamp::domain_max = 0x3FFFF

staticconstexpr

Largest value the exponential decode accepts.

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The documentation for this class was generated from the following file:

• include/tabulasonora/pitch_ramp.hpp