audio.processing.dynamic

Class CompressorEffect

java.lang.Object

audio.processing.dynamic.CompressorEffect

public class CompressorEffect
extends java.lang.Object

**************************************************************************** A Hard-Knee Compressor Effect which allows the user to attenuate the level of signal which is over a threshold set by the user. The attenuation is decided by the 'compression ratio', and the speed at which the signal is attenuated is decided by the attack and release times.

See Also:

Compressor

Constructor Summary

Constructors

Constructor and Description
CompressorEffect(float threshold, double ratio, double attack, double release, double gain, boolean autoGain, java.lang.String detectionType, int thresholdWidth, float sampleRate) Creates a Compressor effect

Method Summary

Methods

Modifier and Type	Method and Description
float	gainSideChain(float inputSam, float attackCoefficient, float releaseCoefficient, short[] array, int n) Sidechain thing to work out...
float	getRegionAverage(short[] currentChunk, int currentPosition) Method to calculate the threshold when 'Regional Average' is selected.
float	getRegionMax(short[] currentChunk, int currentPosition) Method to calculate the threshold when 'Regional Max' is selected.
float	getRegionRMS(short[] currentChunk, int currentPosition) Method to calculate the threshold when 'Regional RMS' is selected.
short[]	process(short[] input) Process method that compresses the audio.
void	setAttackTime(double att) Sets the compressor's attack time in samples, after converting from milliseconds
void	setAutoGain(boolean auto) Selects if the signal will be normalised before outputting
void	setDetectionType(java.lang.String detect) Sets the type of threshold calculator that will be used (Peak, RMS, Region Average or Region Max)
void	setGain(double vol) Sets the make up gain.
void	setRatio(double rat) Sets the compression ratio.
void	setReleaseTime(double rel) Sets the compressors release time in samples, after converting from milliseconds
void	setThreshold(float thresh) Sets the threshold level in DECIBELS.
void	setThresholdWidth(int tWidth) Sets the threshold width that will be used in samples, after converting from milliseconds.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CompressorEffect

public CompressorEffect(float threshold,
                double ratio,
                double attack,
                double release,
                double gain,
                boolean autoGain,
                java.lang.String detectionType,
                int thresholdWidth,
                float sampleRate)

Creates a Compressor effect

Parameters:

threshold - the threshold level in (negative) decibels. When the signal goes over this threshold, compression is applied

ratio - the compression ratio is the ratio of change of the input signal versus the change in the output signal

attack - the time taken before the compressor kicks into action. In milliseconds.

release - the time taken for the compression to stop after the signal falls below the threshold. In milliseconds.

gain - make up gain to boost the signal level after comrpession

autoGain - boolean value to indicate if the user wishes to automatically normalise the audio after compression

detectionType - multiple choice string input which chooses the type of choices by process method to choose suitable method. Chooses between Peak, Region Average, Region Max, and RMS.

thresholdWidth - the size of the window which is the 'region' being examined too be able to set the threshold

sampleRate - the sample rate of the incoming audio

Method Detail

setThreshold

public void setThreshold(float thresh)

Sets the threshold level in DECIBELS. 0dB is the nominal/maximum value, the threshold is therefore relative to this, in negative decibels. This works for short (a maximum of 32767)

Parameters:

thresh - this is an integer value, which is converted to a decibel value, relative to the maximum short value of 32767

setRatio

public void setRatio(double rat)

Sets the compression ratio.

Parameters:

rat - this is compression ratio value. Any samples which are over the threshold level are divided by this value, but first taking into account the attack/release times

setAttackTime

public void setAttackTime(double att)

Sets the compressor's attack time in samples, after converting from milliseconds

Parameters:

att - this is the size of the attack 'delay'. This is used to set delay before the compression is applied, and create the compression envelope

setReleaseTime

public void setReleaseTime(double rel)

Sets the compressors release time in samples, after converting from milliseconds

Parameters:

rel - this is the size of the release 'delay'. This is used before the compression is stopped being applied, and creates the compression release envelope

setGain

public void setGain(double vol)

Sets the make up gain. After the signal is compressed, the audio may be quieter and so the user may wish to increase the volume to compensate. This value is ignored if 'auto gain' is selected.

Parameters:

vol - this can be used to increase the volume of the signal, after compression. This is in decibels (logarithmic).

setDetectionType

public void setDetectionType(java.lang.String detect)

Sets the type of threshold calculator that will be used (Peak, RMS, Region Average or Region Max)

Parameters:

detect - this is the type of threshold calculator which will be used.

setThresholdWidth

public void setThresholdWidth(int tWidth)

Sets the threshold width that will be used in samples, after converting from milliseconds. This is used when region max, region average, and RMS threshold calculators are used. This is essentially a 'window' where only a small part of the audio file is examined. If the user chooses 'Region Average' and sets a threshold width of 10ms, then the average value of the samples in the regions' 'window' is taken

Parameters:

tWidth - this is the threshold width, in milliseconds. This method is used to convert tWidth to samples.

setAutoGain

public void setAutoGain(boolean auto)

Selects if the signal will be normalised before outputting

Parameters:

auto - this is a boolean variable. This is used to to decide if the signal will be normalised to 100%, or if the make up gain is used

getRegionMax

public float getRegionMax(short[] currentChunk,
                 int currentPosition)

Method to calculate the threshold when 'Regional Max' is selected. This calculates the threshold by finding the maximum value in the window of the array which is being considered. The window size is set by the thresholdWidth variable

Parameters:

currentChunk - the current short array or 'audio chunk' being considered. If chunking is not being used, this will stay constant.

currentPosition - the current position of the sample being considered in for loop in the process method.

getRegionAverage

public float getRegionAverage(short[] currentChunk,
                     int currentPosition)

Method to calculate the threshold when 'Regional Average' is selected. This calculates the threshold by finding the average value in the window of the array which is being considered. This can help to give a more subtle and natural compressor sound. The window size is set by the thresholdWidth variable

Parameters:

currentChunk - the current short array or 'audio chunk' being considered. If chunking is not being used, this will stay constant.

currentPosition - the current position of the sample being considered in for loop in the process method.

getRegionRMS

public float getRegionRMS(short[] currentChunk,
                 int currentPosition)

Method to calculate the threshold when 'Regional RMS' is selected. This calculates the threshold by finding the value which is the 'Root Mean Square' in the window of the array which is being considered. This models human hearing more accurately to human hearing. The window size is set by the thresholdWidth variable.

Parameters:

currentChunk - the current short array or 'audio chunk' being considered. If chunking is not being used, this will stay constant.

currentPosition - the current position of the sample being considered in for loop in the process method.

gainSideChain

public float gainSideChain(float inputSam,
                  float attackCoefficient,
                  float releaseCoefficient,
                  short[] array,
                  int n)

Sidechain thing to work out... many things, y'see

Returns:

a short array which has been manipulated.

process

public short[] process(short[] input)

Process method that compresses the audio. A threshold calculator is chosen and the attack and release envelopes are created, to create a subtle compression effect. The values that are over the threshold are divided by the current compression ratio, which is worked out depending on the attack/release times.Works in 32bit (ints) to avoid any (unintentional) clipping from using shorts.

Parameters:

input - short array containing the input data to be manipulated by algorithm

Returns:

a short array which has been manipulated.