Collection of general-purpose constants and routines involved in audio rendering. More...

Namespaces
	Interpolation

	Tables
	Namespace for compile-time generated tables.

Functions
Float	centsToSeconds (Float value)
	Convert cents value into seconds, where There are 1200 cents per power of 2. More...

Float	centsToPower2 (Float value)
	Convert cents value into a power of 2. More...

Float	absoluteCentsToFrequency (Float value)
	Convert cents to frequency, with 0 being 8.175798 Hz. More...

Float	centibelsToAttenuation (Float centibels)
	Convert centiBels to attenuation, where 60 corresponds to a drop of 6dB or 0.5 reduction of audio samples. More...

Float	clampFilterCutoff (Float value)
	Restrict lowpass filter cutoff value to be between 1500 and 13500, inclusive. More...

Float	tenthPercentage (Float value)
	Convert integer from integer [0-1000] into [0.0-1.0]. More...

Float	unipolarToBipolar (Float modulator)
	Translate value in range [0, +1] into one in range [-1, +1]. More...

Float	bipolarToUnipolar (Float modulator)
	Translate value in range [-1, +1] into one in range [0, +1]. More...

Float	unipolarModulate (Float modulator, Float minValue, Float maxValue)
	Perform linear translation from a value in range [0.0, 1.0] into one in [minValue, maxValue]. More...

Float	bipolarModulate (Float modulator, Float minValue, Float maxValue)
	Perform linear translation from a value in range [-1.0, 1.0] into one in [minValue, maxValue]. More...

constexpr Float	parabolicSine (Float angle)
	Estimate sin() value from a radian angle between -PI and PI. More...

void	panLookup (Float pan, Float &left, Float &right)
	Calculate the amount of left and right signal gain in [0.0-1.0] for the given `pan` value which is in range [-500-+500]. More...

Float	sineLookup (Float radians)
	Obtain approximate sine value from table. More...

Float	centsToFrequencyMultiplier (int cent)
	Convert given cents value into a frequency multiplier. More...

Float	centsToFrequency (Float value)
	Quickly convert cent value into a frequency using a table lookup. More...

Float	centibelsToAttenuation (int centibels)
	Convert centibels [0-1441] into an attenuation value from [1.0-0.0]. More...

Float	centibelsToGain (Float centibels)
	Convert centibels [0-1441] into a gain value [0.0-1.0]. More...

Variables
constexpr Float	PI = M_PI

constexpr Float	TwoPI = 2.0 * PI

constexpr Float	HalfPI = PI / 2.0

constexpr Float	QuarterPI = PI / 4.0

constexpr Float	ReferenceNoteFrequency = 440.0

constexpr Float	ReferenceNoteMIDI = 69.0

constexpr Float	ReferenceNoteSemi = ReferenceNoteMIDI * 100

constexpr int	CentsPerSemitone = 100

constexpr int	SemitonePerOctave = 12

constexpr int	CentsPerOctave = 1200

constexpr Float	CentibelsPerDecade = 200.0

constexpr Float	CentsToFrequencyMin = -16000

constexpr Float	CentsToFrequencyMax = 4500

constexpr Float	LowestNoteFrequency = 8.17579891564370697665253828745335

constexpr Float	HalfSquareRoot2 = M_SQRT2 / 2.0

constexpr Float	InterNoteMultiplier = 1.05946309435929530984310531493975

Detailed Description

Collection of general-purpose constants and routines involved in audio rendering.

Function Documentation

◆ absoluteCentsToFrequency()

Float SF2::DSP::absoluteCentsToFrequency ( Float value )

inline

Convert cents to frequency, with 0 being 8.175798 Hz.

Values are clamped to [-16000, 4500].

Parameters

value the value to convert

Returns: frequency in Hz

References CentsToFrequencyMax, CentsToFrequencyMin, centsToPower2(), ReferenceNoteFrequency, and ReferenceNoteSemi.

◆ bipolarModulate()

Float SF2::DSP::bipolarModulate	(	Float	modulator,
		Float	minValue,
		Float	maxValue
	)

inline

Perform linear translation from a value in range [-1.0, 1.0] into one in [minValue, maxValue].

Parameters

modulator	the value to translate
minValue	the lowest value to return when modulator is -1
maxValue	the highest value to return when modulator is +1

Returns: value in range [minValue, maxValue]

◆ bipolarToUnipolar()

Float SF2::DSP::bipolarToUnipolar ( Float modulator )

inline

Translate value in range [-1, +1] into one in range [0, +1].

Parameters

modulator the value to translate

Returns: value in range [0, +1]

◆ centibelsToAttenuation() [1/2]

Float SF2::DSP::centibelsToAttenuation ( Float centibels )

inline

Convert centiBels to attenuation, where 60 corresponds to a drop of 6dB or 0.5 reduction of audio samples.

Note that for raw generator values in an SF2 file, better to use the centibelsToAttenuation(int) value below.

Parameters

centibels the value to convert

Returns: attenuation amount

References CentibelsPerDecade.

◆ centibelsToAttenuation() [2/2]

Float SF2::DSP::centibelsToAttenuation ( int centibels )

inline

Convert centibels [0-1441] into an attenuation value from [1.0-0.0].

Zero indicates no attenuation (1.0), 60 is 0.5, and every 200 is a reduction by 10 (0.1, 0.001, etc.)

Parameters

centibels value to convert

Returns: gain value

References SF2::DSP::Tables::AttenuationLookup::convert().

◆ centibelsToGain()

Float SF2::DSP::centibelsToGain ( Float centibels )

inline

Convert centibels [0-1441] into a gain value [0.0-1.0].

This is the inverse of the above.

Parameters

centibels value to convert

Returns: gain value

References SF2::DSP::Tables::GainLookup::convert().

◆ centsToFrequency()

Float SF2::DSP::centsToFrequency ( Float value )

inline

Quickly convert cent value into a frequency using a table lookup.

These calculations are taken from the Fluid Synth fluid_conv.c file, in particular the fluid_ct2hz_real function. Uses CentPartialLookup above to convert values from 0 - 1199 into the proper multiplier.

References SF2::DSP::Tables::CentsPartialLookup::convert().

Referenced by SF2::Entity::Generator::Definition::convertedValueOf().

◆ centsToFrequencyMultiplier()

Float SF2::DSP::centsToFrequencyMultiplier ( int cent )

inline

Convert given cents value into a frequency multiplier.

Parameters

cent	the value to convert

Returns: multiplier for a frequency that will change the frequency by the given cent value

References SF2::DSP::Tables::CentsFrequencyLookup::convert().

◆ centsToPower2()

Float SF2::DSP::centsToPower2 ( Float value )

inline

Convert cents value into a power of 2.

There are 1200 cents per power of 2.

Parameters

value the value to convert

Returns: power of 2 value

References CentsPerOctave.

Referenced by absoluteCentsToFrequency().

◆ centsToSeconds()

Float SF2::DSP::centsToSeconds ( Float value )

inline

Convert cents value into seconds, where There are 1200 cents per power of 2.

Parameters

value the number to convert

Referenced by SF2::Entity::Generator::Definition::convertedValueOf(), SF2::Render::Envelope::Generator::Modulator(), and SF2::Render::Envelope::Generator::Volume().

◆ clampFilterCutoff()

Float SF2::DSP::clampFilterCutoff ( Float value )

inline

Restrict lowpass filter cutoff value to be between 1500 and 13500, inclusive.

Parameters

value cutoff value

Returns: clamped cutoff value

◆ panLookup()

void SF2::DSP::panLookup	(	Float	pan,
		Float &	left,
		Float &	right
	)

inline

Calculate the amount of left and right signal gain in [0.0-1.0] for the given pan value which is in range [-500-+500].

A pan of -500 is only left, and +500 is only right. A pan of 0 should result in ~0.7078 for both.

Parameters

pan	the value to convert
left	reference to storage for the left gain
right	reference to storage for the right gain

References SF2::DSP::Tables::PanLookup::lookup().

◆ parabolicSine()

constexpr Float SF2::DSP::parabolicSine ( Float angle )

constexpr

Estimate sin() value from a radian angle between -PI and PI.

Derived from code in "Designing Audio Effect Plugins in C++" by Will C. Pirkle (2019) As can be seen in the unit test testParabolicSineAccuracy, the worst-case deviation from std::sin is ~0.0011.

Parameters

angle value between -PI and PI

Returns: approximate sin value

◆ sineLookup()

Float SF2::DSP::sineLookup ( Float radians )

inline

Obtain approximate sine value from table.

Parameters

radians the value to use for theta

Returns: the sine approximation

References SF2::DSP::Tables::SineLookup::sine().

◆ tenthPercentage()

Float SF2::DSP::tenthPercentage ( Float value )

inline

Convert integer from integer [0-1000] into [0.0-1.0].

Parameters

value percentage value expressed as tenths

Returns: normalized value between 0 and 1.

◆ unipolarModulate()

Float SF2::DSP::unipolarModulate	(	Float	modulator,
		Float	minValue,
		Float	maxValue
	)

inline

Perform linear translation from a value in range [0.0, 1.0] into one in [minValue, maxValue].

Parameters

modulator	the value to translate
minValue	the lowest value to return when modulator is 0
maxValue	the highest value to return when modulator is +1

Returns: value in range [minValue, maxValue]

◆ unipolarToBipolar()

Float SF2::DSP::unipolarToBipolar ( Float modulator )

inline

Translate value in range [0, +1] into one in range [-1, +1].

Parameters

modulator the value to translate

Returns: value in range [-1, +1]

Referenced by SF2::DSP::Tables::Generator::generateTransform().

Variable Documentation

◆ CentibelsPerDecade

constexpr Float SF2::DSP::CentibelsPerDecade = 200.0

inlineconstexpr

Referenced by centibelsToAttenuation().

◆ CentsPerOctave

constexpr int SF2::DSP::CentsPerOctave = 1200

inlineconstexpr

Referenced by centsToPower2().

◆ CentsPerSemitone

constexpr int SF2::DSP::CentsPerSemitone = 100

inlineconstexpr

◆ CentsToFrequencyMax

constexpr Float SF2::DSP::CentsToFrequencyMax = 4500

inlineconstexpr

Referenced by absoluteCentsToFrequency().

◆ CentsToFrequencyMin

constexpr Float SF2::DSP::CentsToFrequencyMin = -16000

inlineconstexpr

Referenced by absoluteCentsToFrequency().

◆ HalfPI

constexpr Float SF2::DSP::HalfPI = PI / 2.0

inlineconstexpr

Referenced by SF2::DSP::Tables::SineLookup::sine().

◆ HalfSquareRoot2

constexpr Float SF2::DSP::HalfSquareRoot2 = M_SQRT2 / 2.0

inlineconstexpr

◆ InterNoteMultiplier

constexpr Float SF2::DSP::InterNoteMultiplier = 1.05946309435929530984310531493975

inlineconstexpr

◆ LowestNoteFrequency

constexpr Float SF2::DSP::LowestNoteFrequency = 8.17579891564370697665253828745335

inlineconstexpr

◆ PI

constexpr Float SF2::DSP::PI = M_PI

inlineconstexpr

Referenced by SF2::DSP::Tables::SineLookup::sine().

◆ QuarterPI

constexpr Float SF2::DSP::QuarterPI = PI / 4.0

inlineconstexpr

◆ ReferenceNoteFrequency

constexpr Float SF2::DSP::ReferenceNoteFrequency = 440.0

inlineconstexpr

Referenced by absoluteCentsToFrequency().

◆ ReferenceNoteMIDI

constexpr Float SF2::DSP::ReferenceNoteMIDI = 69.0

inlineconstexpr

◆ ReferenceNoteSemi

constexpr Float SF2::DSP::ReferenceNoteSemi = ReferenceNoteMIDI * 100

inlineconstexpr

Referenced by absoluteCentsToFrequency().

◆ SemitonePerOctave

constexpr int SF2::DSP::SemitonePerOctave = 12

inlineconstexpr

◆ TwoPI

constexpr Float SF2::DSP::TwoPI = 2.0 * PI

inlineconstexpr

Referenced by SF2::DSP::Tables::SineLookup::sine().

Namespaces

Functions

Variables

Detailed Description

Function Documentation

◆ absoluteCentsToFrequency()

◆ bipolarModulate()

◆ bipolarToUnipolar()

◆ centibelsToAttenuation() [1/2]

◆ centibelsToAttenuation() [2/2]

◆ centibelsToGain()

◆ centsToFrequency()

◆ centsToFrequencyMultiplier()

◆ centsToPower2()

◆ centsToSeconds()

◆ clampFilterCutoff()

◆ panLookup()

◆ parabolicSine()

◆ sineLookup()

◆ tenthPercentage()

◆ unipolarModulate()

◆ unipolarToBipolar()

Variable Documentation

◆ CentibelsPerDecade

◆ CentsPerOctave

◆ CentsPerSemitone

◆ CentsToFrequencyMax

◆ CentsToFrequencyMin

◆ HalfPI

◆ HalfSquareRoot2

◆ InterNoteMultiplier

◆ LowestNoteFrequency

◆ PI

◆ QuarterPI

◆ ReferenceNoteFrequency

◆ ReferenceNoteMIDI

◆ ReferenceNoteSemi

◆ SemitonePerOctave

◆ TwoPI