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juce::dsp::Convolution Class Reference

`#include <juce_Convolution.h>`

## Classes

struct | Latency
struct | NonUniform

## Public Types

enum class | Stereo { no , yes }
enum class | Trim { no , yes }
enum class | Normalise { no , yes }

## Public Member Functions

| Convolution ()
| Convolution (ConvolutionMessageQueue &queue)
| Convolution (const Latency &requiredLatency)
| Convolution (const NonUniform &requiredHeadSize)
| Convolution (const Latency &, ConvolutionMessageQueue &)
| Convolution (const NonUniform &, ConvolutionMessageQueue &)
void | prepare (const ProcessSpec &)
void | reset () noexcept
template<typename ProcessContext, std::enable_if_t< std::is_same_v< typename ProcessContext::SampleType, float >, int > = 0>
void | process (const ProcessContext &context) noexcept
void | loadImpulseResponse (const void *sourceData, size_t sourceDataSize, Stereo isStereo, Trim requiresTrimming, size_t size, Normalise requiresNormalisation=Normalise::yes)
void | loadImpulseResponse (const File &fileImpulseResponse, Stereo isStereo, Trim requiresTrimming, size_t size, Normalise requiresNormalisation=Normalise::yes)
void | loadImpulseResponse (AudioBuffer< float > &&buffer, double bufferSampleRate, Stereo isStereo, Trim requiresTrimming, Normalise requiresNormalisation)
int | getCurrentIRSize () const
int | getLatency () const

## Detailed Description

Performs stereo partitioned convolution of an input signal with an impulse response in the frequency domain, using the JUCE FFT class.

This class provides some thread-safe functions to load impulse responses from audio files or memory on-the-fly without noticeable artefacts, performing resampling and trimming if necessary.

The processing performed by this class is equivalent to the time domain convolution done in the FIRFilter class, with a FIRFilter::Coefficients object having the samples of the impulse response as its coefficients. However, in general it is more efficient to do frequency domain convolution when the size of the impulse response is 64 samples or greater.

Note: The default operation of this class uses zero latency and a uniform partitioned algorithm. If the impulse response size is large, or if the algorithm is too CPU intensive, it is possible to use either a fixed latency version of the algorithm, or a simple non-uniform partitioned convolution algorithm.

Threading: It is not safe to interleave calls to the methods of this class. If you need to load new impulse responses during processing the load() calls must be synchronised with process() calls, which in practice means making the load() call from the audio thread. The loadImpulseResponse() functions are wait-free and are therefore suitable for use in a realtime context.

See also
  FIRFilter, FIRFilter::Coefficients, FFT

Definition at line 102 of file juce_Convolution.h.

## Class Documentation

## juce::dsp::Convolution::Latency

struct juce::dsp::Convolution::Latency

Contains configuration information for a convolution with a fixed latency.

Definition at line 117 of file juce_Convolution.h.

Class Members
int | latencyInSamples |

## juce::dsp::Convolution::NonUniform

struct juce::dsp::Convolution::NonUniform

Contains configuration information for a non-uniform convolution.

Definition at line 132 of file juce_Convolution.h.

Class Members
int | headSizeInSamples |

## Member Enumeration Documentation

## Normalise

enum class juce::dsp::Convolution::Normalise

strong

Definition at line 194 of file juce_Convolution.h.

## Stereo

enum class juce::dsp::Convolution::Stereo

strong

Definition at line 192 of file juce_Convolution.h.

## Trim

enum class juce::dsp::Convolution::Trim

strong

Definition at line 193 of file juce_Convolution.h.

## Constructor & Destructor Documentation

## Convolution() [1/6]

juce::dsp::Convolution::Convolution | ( |  | ) |

Initialises an object for performing convolution in the frequency domain.

Definition at line 1197 of file juce_Convolution.cpp.

Referenced by Convolution(), Convolution(), Convolution(), Convolution(), Convolution(), Convolution(), and loadImpulseResponse().

## Convolution() [2/6]

juce::dsp::Convolution::Convolution | ( | ConvolutionMessageQueue & | queue | ) |

explicit

Initialises a convolution engine using a shared background message queue.

IMPORTANT: the queue must remain alive throughout the lifetime of the Convolution.

Definition at line 1201 of file juce_Convolution.cpp.

## Convolution() [3/6]

juce::dsp::Convolution::Convolution | ( | const Latency & | requiredLatency | ) |

explicit

Initialises an object for performing convolution with a fixed latency.

If the requested latency is zero, the actual latency will also be zero. For requested latencies greater than zero, the actual latency will always at least as large as the requested latency. Using a fixed non-zero latency can reduce the CPU consumption of the convolution algorithm.

Parameters

  requiredLatency | the minimum latency

Definition at line 1205 of file juce_Convolution.cpp.

## Convolution() [4/6]

juce::dsp::Convolution::Convolution | ( | const NonUniform & | requiredHeadSize | ) |

explicit

Initialises an object for performing convolution in the frequency domain using a non-uniform partitioned algorithm.

A requiredHeadSize of 256 samples or greater will improve the efficiency of the processing for IR sizes of 4096 samples or greater (recommended for reverberation IRs).

Parameters

  requiredHeadSize | the head IR size for two stage non-uniform partitioned convolution

Definition at line 1211 of file juce_Convolution.cpp.

## Convolution() [5/6]

juce::dsp::Convolution::Convolution | ( | const Latency & | requiredLatency,
|  | ConvolutionMessageQueue & | queue )

Behaves the same as the constructor taking a single Latency argument, but with a shared background message queue.

IMPORTANT: the queue must remain alive throughout the lifetime of the Convolution.

Definition at line 1217 of file juce_Convolution.cpp.

## Convolution() [6/6]

juce::dsp::Convolution::Convolution | ( | const NonUniform & | nonUniform,
|  | ConvolutionMessageQueue & | queue )

Behaves the same as the constructor taking a single NonUniform argument, but with a shared background message queue.

IMPORTANT: the queue must remain alive throughout the lifetime of the Convolution.

Definition at line 1221 of file juce_Convolution.cpp.

## Member Function Documentation

## getCurrentIRSize()

int juce::dsp::Convolution::getCurrentIRSize | ( |  | ) | const

This function returns the size of the current IR in samples.

Definition at line 1290 of file juce_Convolution.cpp.

## getLatency()

int juce::dsp::Convolution::getLatency | ( |  | ) | const

This function returns the current latency of the process in samples.

Note: This is the latency of the convolution engine, not the latency associated with the current impulse response choice that has to be considered separately (linear phase filters, for example).

Definition at line 1292 of file juce_Convolution.cpp.

## loadImpulseResponse() [1/3]

void juce::dsp::Convolution::loadImpulseResponse | ( | AudioBuffer< float > && | buffer,
|  | double | bufferSampleRate,
|  | Stereo | isStereo,
|  | Trim | requiresTrimming,
|  | Normalise | requiresNormalisation )

This function loads an impulse response from an audio buffer. To avoid memory allocation on the audio thread, this function takes ownership of the buffer passed in.

If calling this function during processing, make sure that the buffer is not allocated on the audio thread (be careful of accidental copies!). If you need to pass arbitrary/generated buffers it's recommended to create these buffers on a separate thread and to use some wait-free construct (a lock-free queue or a SpinLock/GenericScopedTryLock combination) to transfer ownership to the audio thread without allocating.

Parameters

  buffer | the AudioBuffer to use
  bufferSampleRate | the sampleRate of the data in the AudioBuffer
  isStereo | selects either stereo or mono
  requiresTrimming | optionally trim the start and the end of the impulse response
  requiresNormalisation | optionally normalise the impulse response amplitude

Definition at line 1252 of file juce_Convolution.cpp.

## loadImpulseResponse() [2/3]

void juce::dsp::Convolution::loadImpulseResponse | ( | const File & | fileImpulseResponse,
|  | Stereo | isStereo,
|  | Trim | requiresTrimming,
|  | size_t | size,
|  | Normalise | requiresNormalisation = Normalise::yes )

This function loads an impulse response from an audio file. It can load any of the audio formats registered in JUCE, and performs some resampling and pre-processing as well if needed.

Parameters

  fileImpulseResponse | the location of the audio file
  isStereo | selects either stereo or mono
  requiresTrimming | optionally trim the start and the end of the impulse response
  size | the expected size for the impulse response after loading, can be set to 0 to requesting the original impulse response size
  requiresNormalisation | optionally normalise the impulse response amplitude

Definition at line 1243 of file juce_Convolution.cpp.

## loadImpulseResponse() [3/3]

void juce::dsp::Convolution::loadImpulseResponse | ( | const void * | sourceData,
|  | size_t | sourceDataSize,
|  | Stereo | isStereo,
|  | Trim | requiresTrimming,
|  | size_t | size,
|  | Normalise | requiresNormalisation = Normalise::yes )

This function loads an impulse response audio file from memory, added in a JUCE project with the Projucer as binary data. It can load any of the audio formats registered in JUCE, and performs some resampling and pre-processing as well if needed.

Note: Don't try to use this function on float samples, since the data is expected to be an audio file in its binary format. Be sure that the original data remains constant throughout the lifetime of the Convolution object, as the loading process will happen on a background thread once this function has returned.

Parameters

  sourceData | the block of data to use as the stream's source
  sourceDataSize | the number of bytes in the source data block
  isStereo | selects either stereo or mono
  requiresTrimming | optionally trim the start and the end of the impulse response
  size | the expected size for the impulse response after loading, can be set to 0 to requesting the original impulse response size
  requiresNormalisation | optionally normalise the impulse response amplitude

Definition at line 1233 of file juce_Convolution.cpp.

Referenced by loadImpulseResponse().

## prepare()

void juce::dsp::Convolution::prepare | ( | const ProcessSpec & | spec | ) |

Must be called before first calling process.

In general, calls to loadImpulseResponse() load the impulse response (IR) asynchronously. The IR will become active once it has been completely loaded and processed, which may take some time.

Calling prepare() will ensure that the IR supplied to the most recent call to loadImpulseResponse() is fully initialised. This IR will then be active during the next call to process(). It is recommended to call loadImpulseResponse() before prepare() if a specific IR must be active during the first process() call.

Definition at line 1261 of file juce_Convolution.cpp.

## process()

template<typename ProcessContext, std::enable_if_t< std::is_same_v< typename ProcessContext::SampleType, float >, int > = 0>

void juce::dsp::Convolution::process | ( | const ProcessContext & | context | ) |

inline noexcept

Performs the filter operation on the given set of samples with optional stereo processing.

Definition at line 186 of file juce_Convolution.h.

Referenced by process().

## reset()

void juce::dsp::Convolution::reset | ( |  | ) |

noexcept

Resets the processing pipeline ready to start a new stream of data.

Definition at line 1268 of file juce_Convolution.cpp.

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

- juce_Convolution.h
- juce_Convolution.cpp