Loudness Meter

Standard-compliant loudness measurements

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Library:
Audio Toolbox / Measurements

Description

TheLoudness Meterblock measures the loudness and true-peak of an audio signal based on EBU R 128 and ITU-R BS.1770-4 standards.

Ports

Input

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`Port_1`— Input signal
matrix | 1-D vector

Matrix input –– Each column of the input is treated as an independent channel. If you use the defaultChannel weights, specify the input channels in order: [Left, Right, Center, Left surround, Right surround].
1-D vector input –– The input is treated as a single channel.

Data Types:single|double

Output

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`M`— Momentary loudness measurement
column vector

The block outputs a column vector with the same data type and number of rows as the input signal.

Data Types:single|double

`S`— Short-term loudness measurement
column vector

The block outputs a column vector with the same data type and number of rows as the input signal.

Data Types:single|double

`TP`— True-peak value
real scalar

The block outputs a real scalar with the same data type as the input signal.

Dependencies

来enable this port, select theOutput true-peak valueparameter.

Data Types:single|double

Parameters

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If a parameter is listed as tunable, then you can change its value during simulation.

`Channel weights`— Linear weighting applied to each input channel
`[1, 1, 1, 1.41, 1.41]`(default) | nonnegative row vector

The number of elements of the row vector must be equal to or greater than the number of input channels. Excess values in the vector are ignored.

The default channel weights follow the ITU-R BS.1170-4 standard. To use the default channel weights, specify the input to theLoudness Meterblock as a matrix whose columns correspond to channels in this order: [Left, Right, Center, Left surround, Right surround].

It is a best practice to specify the channel weights in order: [Left, Right, Center, Left surround, Right surround].

可调:Yes

`Use relative scale for loudness measurements`— Specify block to output loudness measurements relative to target level
off (default) | on

On — The loudness measurements are relative to the value specified byTarget loudness level (LUFS). The output of the block is returned in loudness units (LU).
Off — The loudness measurements are absolute, and returned in loudness units full scale (LUFS).

可调:No

`Target loudness level (LUFS)`— Reference level for relative loudness measurements
`–23`(default) | real scalar

For example, if theTarget loudness level (LUFS)is –23, then a loudness value of –24 LUFS is reported as –1 LU.

可调:Yes

Dependencies

来enable this parameter, select theUse relative scale for loudness measurementsparameter.

`Output true-peak value`— Add output port for true-peak value
off (default) | on

When you select this parameter, an additional output port,TP, is added to the block. TheTPport outputs the true-peak value of the input frame.

可调:No

`Inherit sample rate from input`— Specify source of input sample rate
on (default) | off

When you select this parameter, the block inherits its sample rate from the input signal. When you clear this parameter, you specify the sample rate inInput sample rate (Hz).

可调:No

`Input sample rate (Hz)`— Sample rate of input
`44100`(default) | scalar

可调:Yes

Dependencies

来enable this parameter, clear theInherit sample rate from inputparameter.

`Simulate using`— Specify type of simulation to run
`Code generation`(default) |`Interpreted execution`

Code generation–– Simulate model using generated C code. The first time you run a simulation, Simulink^®generates C code for the block. The C code is reused for subsequent simulations, as long as the model does not change. This option requires additional startup time but the speed of the subsequent simulations is comparable toInterpreted execution.
Interpreted execution–– Simulate model using the MATLAB^®interpreter. This option shortens startup time but has a slower simulation speed thanCode generation. In this mode, you can debug the source code of the block.

可调:No

Model Examples

Compare Loudness Before and After Audio Processing

Measure momentary and short-term loudness before and after compression of a streaming audio signal in Simulink®.

Open Model

Trigger Gain Control Based on Loudness Measurement

This model enables you to apply dynamic range compression to an audio signal while staying inside a preset loudness range. In this model, a Compressor block increases the loudness and decreases the dynamic range of an audio signal. A Loudness Meter block calculates the momentary loudness of the compressed audio signal. If momentary loudness crosses a -23 LUFS threshold, an enabled subsystem applies gain to lower the corresponding level of the audio signal.

Open Model

Block Characteristics

Data Types	`double`\|`single`
Direct Feedthrough	`no`
Multidimensional Signals	`no`
Variable-Size Signals	`yes`
Zero-Crossing Detection	`no`

Algorithms

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TheLoudness Meterblock calculates the momentary loudness, short-term loudness, and true-peak value of an audio signal. You can specify any number of channels and nondefault channel weights used for loudness measurements. The block algorithm is described for the general case ofnchannels and default channel weights.

Loudness Measurements

The input channels,x, pass through a K-weighted filter implemented using the algorithm of theWeighting Filterblock. The K-weighted filter shapes the frequency spectrum to reflect perceived loudness.

Momentary Loudness

The K-weighted channels,y, are divided into 0.4-second segments with 0.3-second overlap. If the required number of samples have not been collected yet, theLoudness Meterblock returns the last computed value for momentary loudness. If enough samples have been collected, then the power (mean square) of each segment of the K-weighted channels is calculated:

$m P_{i} = \frac{1}{w} \sum_{k = 1}^{w} y_{i}^{2} [k]$
- mP_iis the momentary power of theith segment.
- wis the segment length in samples.
The momentary loudness,mL, is computed for each segment:

$m L_{i} = - 0.691 + 10 \log_{10} (\sum_{c = 1}^{n} G_{c} \times m P_{(i, c)}) L U F S$
- G_cis the weighting for channelc.
mLis the momentary loudness returned by yourLoudness Meterblock.

Short-Term Loudness

The K-weighted channels,y, are divided into 3-second segments with 2.9-second overlap. If the required number of samples have not been collected yet, theLoudness Meterblock returns the last computed values for short-term loudness and loudness range. If enough samples have been collected, then the power (mean square) of each K-weighted channel is calculated:

$s P_{i} = \frac{1}{w} \sum_{k = 1}^{w} y_{i}^{2} [k]$
- sP_iis the short-term power of theith segment of a channel.
- wis the segment length in samples.
The short-term loudness,sL, is computed for each segment:

$s L_{i} = - 0.691 + 10 \log_{10} (\sum_{c = 1}^{n} G_{c} \times s P_{(i, c)}) L U F S$
- G_cis the weighting for channelc.
sLis the short-term loudness returned by yourLoudness Meterblock.

True-Peak

Thetrue-peakmeasurement considers only the current input frame of a call to your loudness meter.

信号是至少192千赫采样过量。来optimize processing, the input sample rate determines the exact oversampling. An input sample rate below 750 Hz is not considered.

Input Sample Rate (kHz)	Upsample Factor
[0.75,1.5)	256
[1.5,3)	128
[3,6)	64
[6,12)	32
[12,24)	16
[24,48)	8
[48,96)	4
[96,192)	2
[192,∞)	not required

The oversampled signal,a, passes through a lowpass filter with a half-polyphase length of 12 and stopband attenuation of 80 dB. The filter design usesdesignMultirateFIR.
The filtered signal,b, is rectified and converted to the dB TP scale:

$c = 20 \times \log_{10} (| b |)$
确定了true-peak极限m of the converted signal,c.

References

[1] International Telecommunication Union; Radiocommunication Sector.Algorithms to Measure Audio Programme Loudness and True-Peak Audio Level.ITU-R BS.1770-4. 2015.

[2] European Broadcasting Union.Loudness Normalisation and Permitted Maximum Level of Audio Signals.EBU R 128. 2014.

[3] European Broadcasting Union.Loudness Metering: 'EBU Mode' Metering to Supplement EBU R 128 Loudness Normalization.EBU R 128 Tech 3341. 2014.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2016b

Loudness Meter

Description

Ports

Input

Port_1— Input signalmatrix | 1-D vector

Output

M— Momentary loudness measurementcolumn vector

S— Short-term loudness measurementcolumn vector

TP— True-peak valuereal scalar

Dependencies

Parameters

Channel weights— Linear weighting applied to each input channel[1, 1, 1, 1.41, 1.41](default) | nonnegative row vector

Use relative scale for loudness measurements— Specify block to output loudness measurements relative to target leveloff (default) | on

Target loudness level (LUFS)— Reference level for relative loudness measurements–23(default) | real scalar

Dependencies

Output true-peak value— Add output port for true-peak valueoff (default) | on

Inherit sample rate from input— Specify source of input sample rateon (default) | off

Input sample rate (Hz)— Sample rate of input44100(default) | scalar

Dependencies

Simulate using— Specify type of simulation to runCode generation(default) |Interpreted execution

Model Examples

Compare Loudness Before and After Audio Processing

Trigger Gain Control Based on Loudness Measurement

Block Characteristics

Algorithms

Loudness Measurements

True-Peak

References

Extended Capabilities

C/C++ Code GenerationGenerate C and C++ code using Simulink® Coder™.

Version History

See Also

`Port_1`— Input signal
matrix | 1-D vector

`M`— Momentary loudness measurement
column vector

`S`— Short-term loudness measurement
column vector

`TP`— True-peak value
real scalar

`Channel weights`— Linear weighting applied to each input channel
`[1, 1, 1, 1.41, 1.41]`(default) | nonnegative row vector

`Use relative scale for loudness measurements`— Specify block to output loudness measurements relative to target level
off (default) | on

`Target loudness level (LUFS)`— Reference level for relative loudness measurements
`–23`(default) | real scalar

`Output true-peak value`— Add output port for true-peak value
off (default) | on

`Inherit sample rate from input`— Specify source of input sample rate
on (default) | off

`Input sample rate (Hz)`— Sample rate of input
`44100`(default) | scalar

`Simulate using`— Specify type of simulation to run
`Code generation`(default) |`Interpreted execution`

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.