Public Types | Public Member Functions | Public Attributes | List of all members
dsp::Oversampling< SampleType > Class Template Reference

A processor that performs multi-channel oversampling. More...

Public Types

enum  FilterType { filterHalfBandFIREquiripple = 0, filterHalfBandPolyphaseIIR, numFilterTypes }
 The type of filter that can be used for the oversampling processing. More...
 

Public Member Functions

 Oversampling (size_t numChannels=1)
 The default constructor. More...
 
 Oversampling (size_t numChannels, size_t factor, FilterType type, bool isMaxQuality=true, bool useIntegerLatency=false)
 Constructor. More...
 
 ~Oversampling ()
 Destructor. More...
 
void setUsingIntegerLatency (bool shouldUseIntegerLatency) noexcept
 
SampleType getLatencyInSamples () const noexcept
 Returns the latency in samples of the overall processing. More...
 
size_t getOversamplingFactor () const noexcept
 Returns the current oversampling factor. More...
 
void initProcessing (size_t maximumNumberOfSamplesBeforeOversampling)
 Must be called before any processing, to set the buffer sizes of the internal buffers of the oversampling processing. More...
 
void reset () noexcept
 Resets the processing pipeline, ready to oversample a new stream of data. More...
 
AudioBlock< SampleType > processSamplesUp (const AudioBlock< const SampleType > &inputBlock) noexcept
 Must be called to perform the upsampling, prior to any oversampled processing. More...
 
void processSamplesDown (AudioBlock< SampleType > &outputBlock) noexcept
 Must be called to perform the downsampling, after the upsampling and the non-linear processing. More...
 
void addOversamplingStage (FilterType, float normalisedTransitionWidthUp, float stopbandAmplitudedBUp, float normalisedTransitionWidthDown, float stopbandAmplitudedBDown)
 Adds a new oversampling stage to the Oversampling class, multiplying the current oversampling factor by two. More...
 
void addDummyOversamplingStage ()
 Adds a new "dummy" oversampling stage, which does nothing to the signal. More...
 
void clearOversamplingStages ()
 Removes all the previously registered oversampling stages, so you can add your own from scratch. More...
 

Public Attributes

size_t factorOversampling = 1
 
size_t numChannels = 1
 

Detailed Description

template<typename SampleType>
class dsp::Oversampling< SampleType >

A processor that performs multi-channel oversampling.

This class can be configured to do a factor of 2, 4, 8 or 16 times oversampling, using multiple stages, with polyphase allpass IIR filters or FIR filters, and latency compensation.

The principle of oversampling is to increase the sample rate of a given non-linear process to prevent it from creating aliasing. Oversampling works by upsampling the input signal N times, processing the upsampled signal with the increased internal sample rate, then downsampling the result to get back to the original sample rate.

Choose between FIR or IIR filtering depending on your needs in terms of latency and phase distortion. With FIR filters the phase is linear but the latency is maximised. With IIR filtering the phase is compromised around the Nyquist frequency but the latency is minimised.

See also
FilterDesign.

Member Enumeration Documentation

◆ FilterType

template<typename SampleType >
enum dsp::Oversampling::FilterType

The type of filter that can be used for the oversampling processing.

Enumerator
filterHalfBandFIREquiripple 
filterHalfBandPolyphaseIIR 
numFilterTypes 

Constructor & Destructor Documentation

◆ Oversampling() [1/2]

template<typename SampleType >
dsp::Oversampling< SampleType >::Oversampling ( size_t  numChannels = 1)
explicit

The default constructor.

Note: This creates a "dummy" oversampling stage, which needs to be removed before adding proper oversampling stages.

Parameters
numChannelsthe number of channels to process with this object
See also
clearOversamplingStages, addOversamplingStage

◆ Oversampling() [2/2]

template<typename SampleType >
dsp::Oversampling< SampleType >::Oversampling ( size_t  numChannels,
size_t  factor,
FilterType  type,
bool  isMaxQuality = true,
bool  useIntegerLatency = false 
)

Constructor.

Parameters
numChannelsthe number of channels to process with this object
factorthe processing will perform 2 ^ factor times oversampling
typethe type of filter design employed for filtering during oversampling
isMaxQualityif the oversampling is done using the maximum quality, where the filters will be more efficient but the CPU load will increase as well
useIntegerLatencyif true this processor will add some fractional delay at the end of the signal path to ensure that the overall latency of the oversampling is an integer

◆ ~Oversampling()

template<typename SampleType >
dsp::Oversampling< SampleType >::~Oversampling ( )

Destructor.

Member Function Documentation

◆ setUsingIntegerLatency()

template<typename SampleType >
void dsp::Oversampling< SampleType >::setUsingIntegerLatency ( bool  shouldUseIntegerLatency)
noexcept

◆ getLatencyInSamples()

template<typename SampleType >
SampleType dsp::Oversampling< SampleType >::getLatencyInSamples ( ) const
noexcept

Returns the latency in samples of the overall processing.

You can use this information in your main processor to compensate the additional latency involved with the oversampling, for example with a dry / wet mixer, and to report the latency to the DAW.

Note: If you have not opted to use an integer latency then the latency may not be integer, so you might need to round its value or to compensate it properly in your processing code since plug-ins can only report integer latency values in samples to the DAW.

◆ getOversamplingFactor()

template<typename SampleType >
size_t dsp::Oversampling< SampleType >::getOversamplingFactor ( ) const
noexcept

Returns the current oversampling factor.

◆ initProcessing()

template<typename SampleType >
void dsp::Oversampling< SampleType >::initProcessing ( size_t  maximumNumberOfSamplesBeforeOversampling)

Must be called before any processing, to set the buffer sizes of the internal buffers of the oversampling processing.

◆ reset()

template<typename SampleType >
void dsp::Oversampling< SampleType >::reset ( )
noexcept

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

◆ processSamplesUp()

template<typename SampleType >
AudioBlock<SampleType> dsp::Oversampling< SampleType >::processSamplesUp ( const AudioBlock< const SampleType > &  inputBlock)
noexcept

Must be called to perform the upsampling, prior to any oversampled processing.

Returns an AudioBlock referencing the oversampled input signal, which must be used to perform the non-linear processing which needs the higher sample rate. Don't forget to set the sample rate of that processing to N times the original sample rate.

◆ processSamplesDown()

template<typename SampleType >
void dsp::Oversampling< SampleType >::processSamplesDown ( AudioBlock< SampleType > &  outputBlock)
noexcept

Must be called to perform the downsampling, after the upsampling and the non-linear processing.

The output signal is probably delayed by the internal latency of the whole oversampling behaviour, so don't forget to take this into account.

◆ addOversamplingStage()

template<typename SampleType >
void dsp::Oversampling< SampleType >::addOversamplingStage ( FilterType  ,
float  normalisedTransitionWidthUp,
float  stopbandAmplitudedBUp,
float  normalisedTransitionWidthDown,
float  stopbandAmplitudedBDown 
)

Adds a new oversampling stage to the Oversampling class, multiplying the current oversampling factor by two.

This is used with the default constructor to create custom oversampling chains, requiring a call to the clearOversamplingStages before any addition.

Note: Upsampling and downsampling filtering have different purposes, the former removes upsampling artefacts while the latter removes useless frequency content created by the oversampled process, so usually the attenuation is increased when upsampling compared to downsampling.

Parameters
normalisedTransitionWidthUpa value between 0 and 0.5 which specifies how much the transition between passband and stopband is steep, for upsampling filtering (the lower the better)
stopbandAmplitudedBUpthe amplitude in dB in the stopband for upsampling filtering, must be negative
normalisedTransitionWidthDowna value between 0 and 0.5 which specifies how much the transition between passband and stopband is steep, for downsampling filtering (the lower the better)
stopbandAmplitudedBDownthe amplitude in dB in the stopband for downsampling filtering, must be negative
See also
clearOversamplingStages

◆ addDummyOversamplingStage()

template<typename SampleType >
void dsp::Oversampling< SampleType >::addDummyOversamplingStage ( )

Adds a new "dummy" oversampling stage, which does nothing to the signal.

Using one can be useful if your application features a customisable oversampling factor and if you want to select the current one from an OwnedArray without changing anything in the processing code.

See also
OwnedArray, clearOversamplingStages, addOversamplingStage

◆ clearOversamplingStages()

template<typename SampleType >
void dsp::Oversampling< SampleType >::clearOversamplingStages ( )

Removes all the previously registered oversampling stages, so you can add your own from scratch.

See also
addOversamplingStage, addDummyOversamplingStage

Member Data Documentation

◆ factorOversampling

template<typename SampleType >
size_t dsp::Oversampling< SampleType >::factorOversampling = 1

◆ numChannels

template<typename SampleType >
size_t dsp::Oversampling< SampleType >::numChannels = 1

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