Class SNR

Inheritance

Object

SNR

Inherited Members

Object.Equals(Object)

Object.Equals(Object, Object)

Object.GetHashCode()

Object.GetType()

Object.MemberwiseClone()

Object.ReferenceEquals(Object, Object)

Object.ToString()

Namespace: AudioAnalysisTools.DSP

Assembly: AudioAnalysisTools.dll

Syntax

public class SNR

Constructors

| Improve this Doc View Source

SNR(Double[], Int32[,])

Initializes a new instance of the SNR class. CONSTRUCTOR This constructor is called once from DSP_Frames.ExtractEnvelopeAndAmplSpectrogram().

Declaration

public SNR(double[] signal, int[, ] frameIDs)

Parameters

Type	Name	Description
Double[]	signal	signal.
Int32[,]	frameIDs	the start and end index of every frame.

Fields

| Improve this Doc View Source

DefaultNhBgThreshold

Declaration

public const double DefaultNhBgThreshold = 2

Field Value

Type	Description
Double

| Improve this Doc View Source

DefaultStddevCount

Declaration

public const double DefaultStddevCount = 0

Field Value

Type	Description
Double

| Improve this Doc View Source

FractionalBoundForLowPercentile

Declaration

public const double FractionalBoundForLowPercentile = 0.2

Field Value

Type	Description
Double

| Improve this Doc View Source

FractionalBoundForMode

Declaration

public const double FractionalBoundForMode = 0.95

Field Value

Type	Description
Double

| Improve this Doc View Source

KeyDynamicRange

Declaration

public const string KeyDynamicRange = "DYNAMIC_RANGE"

Field Value

Type	Description
String

| Improve this Doc View Source

KeyNoiseReductionType

Declaration

public const string KeyNoiseReductionType = "NOISE_REDUCTION_TYPE"

Field Value

Type	Description
String

| Improve this Doc View Source

MaxLogEnergyReference

Declaration

public const double MaxLogEnergyReference = 0

Field Value

Type	Description
Double

| Improve this Doc View Source

MinimumDbBoundForEnvironmentalNoise

Reference dB levels for recording of very silent environment Used as minimum bound when normalising dB values. This value was based on actual recording of cold winter morning (Gympie) using an SM2. However, SM4 has a lower noise level. Consequently this value lowered to -90 on 7th August 2018.

Declaration

public const double MinimumDbBoundForEnvironmentalNoise = -90

Field Value

Type	Description
Double

| Improve this Doc View Source

MinimumDbBoundForZeroSignal

Reference dB levels for a zero signal Used as minimum bound when normalising dB values. This value was based on the observation of an actual zero signal on an SM2. However, SM4 has a lower noise level. Consequently this value lowered to -100 on 7th August 2018.

Declaration

public const double MinimumDbBoundForZeroSignal = -100

Field Value

Type	Description
Double

| Improve this Doc View Source

MinLogEnergyReference

Reference logEnergies for signal segmentation, energy normalisation etc MinLogEnergyReference was changed from -6.0 to -8.0 on 6th August 2018 to accommodate signals with extended zero values. Typical noise value using Jason Wimmer original handheld recorders was = -4.5 = -45dB Typical noise value for quiet recordings with SM4 = -8.0 or -9.0, i.e. -80 to -90 dB.

Declaration

public const double MinLogEnergyReference = -8

Field Value

Type	Description
Double

Properties

| Improve this Doc View Source

FractionOfHighEnergyFrames

Declaration

public double FractionOfHighEnergyFrames { get; set; }

Property Value

Type	Description
Double

| Improve this Doc View Source

FrameDecibels

Gets or sets the FrameDecibels array. Calculate as dB[i] = 10 x log-energy of frame[i]. Appears only to be used to determine the fraction of high energy frames.

Declaration

public double[] FrameDecibels { get; set; }

Property Value

Type	Description
Double[]

| Improve this Doc View Source

MaxDb

Declaration

public double MaxDb { get; set; }

Property Value

Type	Description
Double

| Improve this Doc View Source

MaxReferenceDecibelsWrtNoise

Declaration

public double MaxReferenceDecibelsWrtNoise { get; set; }

Property Value

Type	Description
Double

| Improve this Doc View Source

MinDb

Declaration

public double MinDb { get; set; }

Property Value

Type	Description
Double

| Improve this Doc View Source

ModalNoiseProfile

Declaration

public double[] ModalNoiseProfile { get; set; }

Property Value

Type	Description
Double[]

| Improve this Doc View Source

NoiseRange

Declaration

public double NoiseRange { get; set; }

Property Value

Type	Description
Double

| Improve this Doc View Source

NoiseSubtracted

Declaration

public double NoiseSubtracted { get; set; }

Property Value

Type	Description
Double

| Improve this Doc View Source

Snr

Gets or sets Snr. SNR = max_dB - Q that is, max decibels minus the modal noise This is notation used by Lamel et al.

Declaration

public double Snr { get; set; }

Property Value

Type	Description
Double

Methods

| Improve this Doc View Source

Calculate_SNR_ShortRecording(FileInfo, Dictionary<String, String>, TimeSpan, TimeSpan, Int32, Int32, Double)

This method written 18-09-2014 to process Xueyan's query recordings. Calculate the SNR statistics for each recording and then write info back to csv file.

Declaration

public static SNR.SnrStatistics Calculate_SNR_ShortRecording(FileInfo sourceRecording, Dictionary<string, string> configDict, TimeSpan start, TimeSpan duration, int minHz, int maxHz, double threshold)

Parameters

Type	Name	Description
FileInfo	sourceRecording
Dictionary<String, String>	configDict
TimeSpan	start
TimeSpan	duration
Int32	minHz
Int32	maxHz
Double	threshold

Returns

Type	Description
SNR.SnrStatistics

| Improve this Doc View Source

CalculateFreqBandAvIntensity(Double[,], Int32, Int32, Int32)

Calculates the mean intensity in a freq band defined by its min and max freq. THis method averages dB log values incorrectly but it is faster than doing many log conversions. This method is used to find acoustic events and is accurate enough for the purpose.

Declaration

public static double[] CalculateFreqBandAvIntensity(double[, ] sonogram, int minHz, int maxHz, int nyquist)

Parameters

Type	Name	Description
Double[,]	sonogram
Int32	minHz
Int32	maxHz
Int32	nyquist

Returns

Type	Description
Double[]

| Improve this Doc View Source

CalculateFreqBandAvIntensityMinusBufferIntensity(Double[,], Int32, Int32, Int32, Int32, Int32)

Calculates the average intensity in a freq band having min and max freq, AND then subtracts average intensity in the side/buffer bands, below and above. THis method adds dB log values incorrectly but it is faster than doing many log conversions. This method is used to find acoustic events and is accurate enough for the purpose.

Declaration

public static double[] CalculateFreqBandAvIntensityMinusBufferIntensity(double[, ] sonogramData, int minHz, int maxHz, int bottomHzBuffer, int topHzBuffer, int nyquist)

Parameters

Type	Name	Description
Double[,]	sonogramData
Int32	minHz
Int32	maxHz
Int32	bottomHzBuffer
Int32	topHzBuffer
Int32	nyquist

Returns

Type	Description
Double[]

| Improve this Doc View Source

CalculateLogEnergyOfsignalFrames(Double[], Int32[,])

Returns the log(energy) in each frame of the signal. The energy of a frame is the log of the summed energy of all the samples in the frame. Normally, if the passed frames are FFT spectra, then would multiply by 2 because spectra are symmetrical about Nyquist. BUT this method returns the AVERAGE sample energy, which therefore normalises for frame length / sample number.

Energy normalisation formula taken from Lecture Notes of Prof. Bryan Pellom Automatic Speech Recognition: From Theory to Practice. http://www.cis.hut.fi/Opinnot/T-61.184/ September 27th 2004.

Calculate normalised energy of frame as energy[i] = logEnergy - maxLogEnergy; This is same as log10(logEnergy / maxLogEnergy) ie normalised to a fixed maximum energy value.

Declaration

public static double[] CalculateLogEnergyOfsignalFrames(double[] signal, int[, ] frameIDs)

Parameters

Type	Name	Description
Double[]	signal
Int32[,]	frameIDs

Returns

Type	Description
Double[]

| Improve this Doc View Source

CalculateLogEnergyOfsignalFrames(Double[,])

NOTE: This method is identical to the above one, except that the actual frames are passed rather than the starts and ends of the frames.

Declaration

public static double[] CalculateLogEnergyOfsignalFrames(double[, ] frames)

Parameters

Type	Name	Description
Double[,]	frames

Returns

Type	Description
Double[]

| Improve this Doc View Source

CalculateModalBackgroundNoiseInSignal(Double[], Double)

Declaration

public static SNR.BackgroundNoise CalculateModalBackgroundNoiseInSignal(double[] array, double sdCount)

Parameters

Type	Name	Description
Double[]	array
Double	sdCount

Returns

Type	Description
SNR.BackgroundNoise

| Improve this Doc View Source

CalculateSnrInFreqBand(BaseSonogram, TimeSpan, TimeSpan, Int32, Int32, Double)

Calculates the matrix row/column bounds given the real world bounds. Axis scales are obtained form the passed sonogram instance.

Declaration

public static SNR.SnrStatistics CalculateSnrInFreqBand(BaseSonogram sonogram, TimeSpan startTime, TimeSpan extractDuration, int minHz, int maxHz, double threshold)

Parameters

Type	Name	Description
BaseSonogram	sonogram
TimeSpan	startTime
TimeSpan	extractDuration
Int32	minHz
Int32	maxHz
Double	threshold

Returns

Type	Description
SNR.SnrStatistics

| Improve this Doc View Source

CalculateSnrInFreqBand(Double[,], Int32, Int32, Int32, Int32, Double)

The calculation of SNR in this method assumes that background noise has already been removed. That is, the maximum value is with respect to zero. SNR should be calculated based on power values in decibel units. i.e. SNR = 10log(PowerOfSignal / PowerOfNoise); or SNR = 20log(Signal amplitude) - 20log(Noise amplitude); If the passed sonogram data is amplitude or energy values (rather than decibel values) then the returned SNR value needs to be appropriately corrected.

Declaration

public static SNR.SnrStatistics CalculateSnrInFreqBand(double[, ] sonogramData, int startframe, int frameSpan, int minBin, int maxBin, double threshold)

Parameters

Type	Name	Description
Double[,]	sonogramData
Int32	startframe
Int32	frameSpan
Int32	minBin
Int32	maxBin
Double	threshold

Returns

Type	Description
SNR.SnrStatistics

| Improve this Doc View Source

CalculateWhistleIntensity(Double[,], Int32, Int32, Int32, Int32, Int32)

Declaration

public static double[] CalculateWhistleIntensity(double[, ] sonogramData, int minHz, int maxHz, int bottomHzBuffer, int topHzBuffer, int nyquist)

Parameters

Type	Name	Description
Double[,]	sonogramData
Int32	minHz
Int32	maxHz
Int32	bottomHzBuffer
Int32	topHzBuffer
Int32	nyquist

Returns

Type	Description
Double[]

| Improve this Doc View Source

ConvertLogEnergy2Decibels(Double[])

Declaration

public static double[] ConvertLogEnergy2Decibels(double[] logEnergy)

Parameters

Type	Name	Description
Double[]	logEnergy

Returns

Type	Description
Double[]

| Improve this Doc View Source

DecibelsInSubband(Double[,], Int32, Int32, Double)

Declaration

public static double[] DecibelsInSubband(double[, ] dBMatrix, int minHz, int maxHz, double freqBinWidth)

Parameters

Type	Name	Description
Double[,]	dBMatrix
Int32	minHz
Int32	maxHz
Double	freqBinWidth

Returns

Type	Description
Double[]

| Improve this Doc View Source

GetModeAndOneStandardDeviation(Double[], out Int32, out Int32)

This is the important part of Lamel's algorithm. It assumes an additive noise model. That is, it assumes that the passed histogram represents the distribution of values in a waveform consisting of a signal plus added Gaussian noise. This method estimates the mean and SD of the noise.

Declaration

public static void GetModeAndOneStandardDeviation(double[] histo, out int indexOfMode, out int indexOfOneSd)

Parameters

Type	Name	Description
Double[]	histo
Int32	indexOfMode
Int32	indexOfOneSd

| Improve this Doc View Source

KeyToNoiseReductionType(String)

Converts a string interpreted as a key to a NoiseReduction Type.

Declaration

public static NoiseReductionType KeyToNoiseReductionType(string key)

Parameters

Type	Name	Description
String	key	The string to convert.

Returns

Type	Description
NoiseReductionType	A NoiseReductionType enumeration.

| Improve this Doc View Source

NoiseReduce(Double[,], NoiseReductionType, Double)

Removes noise from a spectrogram. Choice of methods. Make sure that do MelScale reduction BEFORE applying noise filter.

Declaration

public static Tuple<double[, ], double[]> NoiseReduce(double[, ] m, NoiseReductionType nrt, double parameter)

Parameters

Type	Name	Description
Double[,]	m
NoiseReductionType	nrt
Double	parameter

Returns

Type	Description
Tuple<Double[,], Double[]>

| Improve this Doc View Source

NoiseReduce_FixedRange(Double[,], Double, Double)

IMPORTANT: Mel scale conversion should be done before noise reduction.

Declaration

public static double[, ] NoiseReduce_FixedRange(double[, ] matrix, double dynamicRange, double sdCount)

Parameters

Type	Name	Description
Double[,]	matrix
Double	dynamicRange
Double	sdCount

Returns

Type	Description
Double[,]

| Improve this Doc View Source

NoiseReduce_FlattenAndTrim(Double[,], Double)

Declaration

public static double[, ] NoiseReduce_FlattenAndTrim(double[, ] matrix, double stdDevCount)

Parameters

Type	Name	Description
Double[,]	matrix
Double	stdDevCount

Returns

Type	Description
Double[,]

| Improve this Doc View Source

NoiseReduce_Mean(Double[,], Double)

The passed matrix is the decibel spectrogram.

Declaration

public static double[, ] NoiseReduce_Mean(double[, ] matrix, double nhBackgroundThreshold)

Parameters

Type	Name	Description
Double[,]	matrix
Double	nhBackgroundThreshold

Returns

Type	Description
Double[,]

| Improve this Doc View Source

NoiseReduce_Median(Double[,], Double)

The passed matrix is the decibel spectrogram.

Declaration

public static double[, ] NoiseReduce_Median(double[, ] matrix, double nhBackgroundThreshold)

Parameters

Type	Name	Description
Double[,]	matrix
Double	nhBackgroundThreshold

Returns

Type	Description
Double[,]

| Improve this Doc View Source

NoiseReduce_Standard(Double[,])

expects a spectrogram in dB values IMPORTANT: Mel scale conversion should be done before noise reduction Uses default values for severity of noise reduction and neighbourhood threshold.

Declaration

public static double[, ] NoiseReduce_Standard(double[, ] matrix)

Parameters

Type	Name	Description
Double[,]	matrix

Returns

Type	Description
Double[,]

| Improve this Doc View Source

NoiseReduce_Standard(Double[,], Double[], Double)

expects a spectrogram in dB values.

Declaration

public static double[, ] NoiseReduce_Standard(double[, ] matrix, double[] noiseProfile, double nhBackgroundThreshold)

Parameters

Type	Name	Description
Double[,]	matrix
Double[]	noiseProfile
Double	nhBackgroundThreshold

Returns

Type	Description
Double[,]

| Improve this Doc View Source

NormaliseDecibelArray_ZeroOne(Double[], Double)

NormaliseMatrixValues the power values using the passed reference decibel level. NOTE: This method assumes that the energy values are in decibels and that they have been scaled so that the modal noise value = 0 dB. Simply truncate all values below this to zero dB.

Declaration

public static double[] NormaliseDecibelArray_ZeroOne(double[] dB, double maxDecibels)

Parameters

Type	Name	Description
Double[]	dB
Double	maxDecibels

Returns

Type	Description
Double[]

| Improve this Doc View Source

ReduceFreqBinsInSpectrogram(Double[,], Int32)

returns a spectrogram with reduced number of frequency bins.

Declaration

public static double[, ] ReduceFreqBinsInSpectrogram(double[, ] inSpectro, int subbandCount)

Parameters

Type	Name	Description
Double[,]	inSpectro	input spectrogram.
Int32	subbandCount	numbre of req bands in output spectrogram.

Returns

Type	Description
Double[,]

| Improve this Doc View Source

RemoveNeighbourhoodBackgroundNoise(Double[,], Double)

This method sets a sonogram pixel value = minimum value in sonogram if average pixel value in its neighbourhood is less than min+threshold. Typically would expect min value in sonogram = zero.

Declaration

public static double[, ] RemoveNeighbourhoodBackgroundNoise(double[, ] matrix, double nhThreshold)

Parameters

Type	Name	Description
Double[,]	matrix	the sonogram.
Double	nhThreshold	user defined threshold. Typically in range 2-4 dB.

Returns

Type	Description
Double[,]

| Improve this Doc View Source

RmsNormalization(Double[,])

Root Mean Square (RMS) Normalization Matrix is assumed to be a spectrogram Divides the spectrogram values by the RMS in order to adjust for varying levels of signal strength.

Declaration

public static double[, ] RmsNormalization(double[, ] matrix)

Parameters

Type	Name	Description
Double[,]	matrix

Returns

Type	Description
Double[,]

| Improve this Doc View Source

SegmentArrayOfIntensityvalues(Double[], Double, Int32)

Declaration

public static List<int[]> SegmentArrayOfIntensityvalues(double[] values, double threshold, int minLength)

Parameters

Type	Name	Description
Double[]	values
Double	threshold
Int32	minLength

Returns

Type	Description
List<Int32[]>

| Improve this Doc View Source

SetDynamicRange(Double[,], Double, Double)

sets the dynamic range in dB for a sonogram. All intensity values are shifted so that the max intensity value = maxDB parameter. All values which fall below the minDB parameter are then set = to minDB.

Declaration

public static double[, ] SetDynamicRange(double[, ] m, double minDb, double maxDb)

Parameters

Type	Name	Description
Double[,]	m	The spectral sonogram passes as matrix of doubles.
Double	minDb	minimum decibel value.
Double	maxDb	maximum decibel value.

Returns

Type	Description
Double[,]

| Improve this Doc View Source

SetLocalBounds(Double[,], Int32, Int32, Int32, Int32)

SetLocalBounds.

Declaration

public static double[, ] SetLocalBounds(double[, ] m, int minPercentileBound, int maxPercentileBound, int temporalNh, int freqBinNh)

Parameters

Type	Name	Description
Double[,]	m	The spectral sonogram passes as matrix of doubles.
Int32	minPercentileBound	minimum decibel value.
Int32	maxPercentileBound	maximum decibel value.
Int32	temporalNh	buffer in temporal dimension.
Int32	freqBinNh	buffer in frequency dimension.

Returns

Type	Description
Double[,]

| Improve this Doc View Source

Signal2Decibels(Double[])

Declaration

public static double[] Signal2Decibels(double[] signal)

Parameters

Type	Name	Description
Double[]	signal

Returns

Type	Description
Double[]

| Improve this Doc View Source

SubbandIntensity_NoiseReduced(Double[,], Int32, Int32, Int32, Double, Double)

Declaration

public static Tuple<double[], double, double> SubbandIntensity_NoiseReduced(double[, ] sonogram, int minHz, int maxHz, int nyquist, double smoothDuration, double framesPerSec)

Parameters

Type	Name	Description
Double[,]	sonogram	sonogram of signal - values in dB.
Int32	minHz	min of freq band to sample.
Int32	maxHz	max of freq band to sample.
Int32	nyquist	signal nyquist - used to caluclate hz per bin.
Double	smoothDuration	window width (in seconds) to smooth sig intenisty.
Double	framesPerSec	time scale of the sonogram.

Returns

Type	Description
Tuple<Double[], Double, Double>

| Improve this Doc View Source

SubtractAndTruncate2Zero(Double[], Double)

Declaration

public static double[] SubtractAndTruncate2Zero(double[] inArray, double threshold)

Parameters

Type	Name	Description
Double[]	inArray
Double	threshold

Returns

Type	Description
Double[]

| Improve this Doc View Source

SubtractAndTruncateNoiseProfile(Double[,], Double[], Double)

Subtracts the supplied noise profile from spectorgram AND sets values less than backgroundThreshold to ZERO.

Declaration

public static double[, ] SubtractAndTruncateNoiseProfile(double[, ] matrix, double[] noiseProfile, double backgroundThreshold)

Parameters

Type	Name	Description
Double[,]	matrix
Double[]	noiseProfile
Double	backgroundThreshold

Returns

Type	Description
Double[,]

| Improve this Doc View Source

SubtractBackgroundNoise_dB()

subtract background noise to produce a decibels array in which zero dB = modal noise DOES NOT TRUNCATE BELOW ZERO VALUES.

Declaration

public void SubtractBackgroundNoise_dB()

| Improve this Doc View Source

SubtractBackgroundNoiseFromSignal(Double[], Double)

Calculates and subtracts the background noise value from an array of double. Used for calculating and removing the background noise and setting baseline = zero. Implements a MODIFIED version of Lamel et al. They only search in range 10dB above min dB whereas this method sets upper limit to 66% of range of intensity values. ASSUMES ADDITIVE MODEL with GAUSSIAN NOISE. Values below zero set equal to zero. This method can be called for any array of signal values but is PRESUMED TO BE A WAVEFORM or FREQ BIN OF HISTOGRAM.

Declaration

public static SNR.BackgroundNoise SubtractBackgroundNoiseFromSignal(double[] array, double sdCount)

Parameters

Type	Name	Description
Double[]	array
Double	sdCount

Returns

Type	Description
SNR.BackgroundNoise

| Improve this Doc View Source

SubtractBackgroundNoiseFromWaveform_dB(Double[], Double)

Calls method to implement the "Adaptive Level Equalisatsion" algorithm of (Lamel et al, 1981) It has the effect of setting background noise level to 0 dB. Passed signal array MUST be in deciBels. ASSUMES an ADDITIVE MODEL with GAUSSIAN NOISE. Calculates the average and standard deviation of the noise and then calculates a noise threshold. Then subtracts threshold noise from the signal - so now zero dB = threshold noise Sets default values for min dB value and the noise threshold. 10 dB is a default used by Lamel et al. RETURNS: 1) noise reduced decibel array; 2) Q - the modal BG level; 3) min value 4) max value; 5) snr; and 6) SD of the noise.

Declaration

public static SNR.BackgroundNoise SubtractBackgroundNoiseFromWaveform_dB(double[] dBarray, double sdCount)

Parameters

Type	Name	Description
Double[]	dBarray
Double	sdCount

Returns

Type	Description
SNR.BackgroundNoise

| Improve this Doc View Source

SubtractBgNoiseFromSpectrogram(Double[,], Double[])

Subtracts the supplied modal noise value for each freq bin BUT DOES NOT set negative values to zero.

Declaration

public static double[, ] SubtractBgNoiseFromSpectrogram(double[, ] matrix, double[] noiseProfile)

Parameters

Type	Name	Description
Double[,]	matrix
Double[]	noiseProfile

Returns

Type	Description
Double[,]

| Improve this Doc View Source

TruncateBgNoiseFromSpectrogram(Double[,], Double[])

Subtracts the supplied noise profile from spectorgram AND sets negative values to ZERO.

Declaration

public static double[, ] TruncateBgNoiseFromSpectrogram(double[, ] matrix, double[] noiseProfile)

Parameters

Type	Name	Description
Double[,]	matrix
Double[]	noiseProfile

Returns

Type	Description
Double[,]

| Improve this Doc View Source

TruncateNegativeValues2Zero(Double[])

Declaration

public static double[] TruncateNegativeValues2Zero(double[] inArray)

Parameters

Type	Name	Description
Double[]	inArray

Returns

Type	Description
Double[]

Extension Methods

ObjectExtensions.NotNull(Object)

ObjectExtensions.AsArray<T>(T)

ObjectExtensions.AsList<T>(T)

ObjectExtensions.Wrap<T>(T)

SystemExtensions.BinarySerialize(Object)

ConfigFileExtensions.NotNull(Object, FileInfo, String, String)

ConfigFileExtensions.ValidateNotNull(Object, String, String)

ConfigFileExtensions.ValidateLessThan<T>(Object, Nullable<T>, String, Nullable<T>, String, String)

ExtensionsXml.SerializeObject<T>(T)