The delay-line effect described by Jon Dattorro in "Effect Design Part 2: Delay-Line Modulation and Chorus", J. More...

#include <dattorro_delay.h>

Inheritance diagram for sfFDN::DattorroDelay:

Collaboration diagram for sfFDN::DattorroDelay:

Public Member Functions
	DattorroDelay (const DattorroDelayOptions &options={})
	Constructs a Dattorro delay-line effect.

void	SetBlend (float blend) noexcept SFFDN_NONBLOCKING
	Sets the gain applied to the input of the delay line.

float	GetBlend () const noexcept SFFDN_NONBLOCKING
	Returns the gain applied to the input of the delay line.

void	SetFeedforward (float feedforward) noexcept SFFDN_NONBLOCKING
	Sets the gain applied to the modulated output of the delay line.

float	GetFeedforward () const noexcept SFFDN_NONBLOCKING
	Returns the gain applied to the modulated output of the delay line.

void	SetFeedback (float feedback) noexcept SFFDN_NONBLOCKING
	Sets the gain applied to the fixed output of the delay line before it is fed back into the delay line.

float	GetFeedback () const noexcept SFFDN_NONBLOCKING
	Returns the gain applied to the fixed output of the delay line.

void	SetDelay (float delay)
	Sets the nominal delay of the delay line.

float	GetDelay () const
	Returns the nominal delay of the delay line, in samples.

void	SetMod (const ModulationOptions &options)
	Sets the modulation applied to the feedforward tap.

float	Tick (float input) noexcept SFFDN_NONBLOCKING
	Processes a single sample.

void	Process (const AudioBuffer &input, AudioBuffer &output) noexcept SFFDN_NONBLOCKING override
	Processes the audio buffer.

uint32_t	InputChannelCount () const noexcept SFFDN_NONBLOCKING override
	Returns the number of input channels this processor expects.

uint32_t	OutputChannelCount () const noexcept SFFDN_NONBLOCKING override
	Returns the number of output channels this processor produces.

void	Clear () override
	Clears the delay line and resets the modulation phase.

std::unique_ptr< AudioProcessor >	Clone () const override
	Creates a copy of the processor.

Public Member Functions inherited from sfFDN::AudioProcessor

Static Public Attributes
static constexpr float	kMinimumDelay = 2.f
	The smallest delay, in samples, that the delay line is allowed to take.

Additional Inherited Members
Protected Member Functions inherited from sfFDN::AudioProcessor
	AudioProcessor (const AudioProcessor &)=default

AudioProcessor &	operator= (const AudioProcessor &)=default

	AudioProcessor (AudioProcessor &&) noexcept=default

AudioProcessor &	operator= (AudioProcessor &&) noexcept=default

Detailed Description

The delay-line effect described by Jon Dattorro in "Effect Design Part 2: Delay-Line Modulation and Chorus", J.

Audio Eng. Soc., Vol. 45, No. 10, 1997.

A single delay line is read at two taps and wrapped in a comb filter with three knobs: blend, feedforward and feedback.

\[ w[n] = x[n] - \mathit{FB} \cdot w[n - M] \\ y[n] = \mathit{FF} \cdot w[n - M(n)] + \mathit{BL} \cdot w[n] \]

The feedback tap sits at the fixed nominal delay \(M\) and is read without interpolation. Only the feedforward tap is modulated: it is read with interpolation at \(M(n) = M + \mathit{width} \cdot \sin(2 \pi f n)\). Modulating the feedback tap would change the length of the recirculating loop on every sample, so it is deliberately left fixed.

Vibrato, flanging, chorus, doubling and echo are all obtained from this one structure by changing the three gains. See MakeDattorroDelayOptions().

Note: The feedback is subtracted at the summing junction, as drawn in the paper. A positive feedback gain therefore recirculates with inverted polarity, and the gains of Table 1 can be used exactly as printed. See MakeDattorroDelayOptions().; Choose the interpolation type to match how the delay is used. Linear interpolation is the cheaper choice on a modulated tap and its magnitude droop near Nyquist is inaudible for an insert effect, which is what the presets returned by MakeDattorroDelayOptions() use. Allpass interpolation costs a little more but has a flat magnitude response; prefer it whenever the effect sits inside a feedback loop, where the droop of linear interpolation compounds on every circulation and pulls the high-frequency T60 below target. Allpass interpolation is safe on a modulated tap: DelayInterp::SetDelay() re-seeds the allpass state from the new tap whenever the integer part of the delay changes, so crossing a sample boundary no longer leaves a step in the output.

Constructor & Destructor Documentation

◆ DattorroDelay()

sfFDN::DattorroDelay::DattorroDelay ( const DattorroDelayOptions & options = {} )

explicit

Constructs a Dattorro delay-line effect.

Parameters

options The configuration options for the effect.

Note: The instantaneous delay is never allowed to fall below kMinimumDelay samples. The constructor throws std::invalid_argument if the nominal delay minus the modulation width is smaller than that.; The fixed feedback tap is placed at the nearest integer to the nominal delay, since it is read without interpolation. The modulated feedforward tap keeps the fractional part of the nominal delay.

Member Function Documentation

◆ Clear()

void sfFDN::DattorroDelay::Clear ( )

overridevirtual

Clears the delay line and resets the modulation phase.

The three gains are left untouched.

Implements sfFDN::AudioProcessor.

◆ Clone()

std::unique_ptr< AudioProcessor > sfFDN::DattorroDelay::Clone ( ) const

overridevirtual

Creates a copy of the processor.

Returns: A unique pointer to the cloned processor.

Implements sfFDN::AudioProcessor.

◆ InputChannelCount()

uint32_t sfFDN::DattorroDelay::InputChannelCount ( ) const

overridevirtualnoexcept

Returns the number of input channels this processor expects.

This is always 1.

Implements sfFDN::AudioProcessor.

◆ OutputChannelCount()

uint32_t sfFDN::DattorroDelay::OutputChannelCount ( ) const

overridevirtualnoexcept

Returns the number of output channels this processor produces.

This is always 1.

Implements sfFDN::AudioProcessor.

◆ Process()

void sfFDN::DattorroDelay::Process	(	const AudioBuffer &	input,
		AudioBuffer &	output )

overridevirtualnoexcept

Processes the audio buffer.

Parameters

input	The input audio buffer.
output	The output audio buffer.

Note: The input and output buffers must have one channel and the same number of samples.

Implements sfFDN::AudioProcessor.

◆ SetDelay()

void sfFDN::DattorroDelay::SetDelay ( float delay )

Sets the nominal delay of the delay line.

Parameters

delay The delay in samples.

Note: This moves both the fixed feedback tap and the center of the modulated feedforward tap.; Throws std::invalid_argument if the delay minus the current modulation width is smaller than kMinimumDelay.

◆ SetFeedback()

void sfFDN::DattorroDelay::SetFeedback ( float feedback )

noexcept

Sets the gain applied to the fixed output of the delay line before it is fed back into the delay line.

Parameters

feedback The feedback gain. The value is clamped to the range (-1, 1) to keep the loop stable.

◆ SetMod()

void sfFDN::DattorroDelay::SetMod ( const ModulationOptions & options )

Sets the modulation applied to the feedforward tap.

Parameters

options The modulation options. The amplitude is the peak deviation, in samples, of the feedforward tap around the nominal delay.

Note: Throws std::invalid_argument if the nominal delay minus the amplitude is smaller than kMinimumDelay.

◆ Tick()

float sfFDN::DattorroDelay::Tick ( float input )

noexcept

Processes a single sample.

Parameters

input The input sample.

Returns: The output sample.

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

include/sffdn/dattorro_delay.h

Public Member Functions

Static Public Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ DattorroDelay()

Member Function Documentation

◆ Clear()

◆ Clone()

◆ InputChannelCount()

◆ OutputChannelCount()

◆ Process()

◆ SetDelay()

◆ SetFeedback()

◆ SetMod()

◆ Tick()