splMeter
Measure sound pressure level of audio signal
Description
The splMeter
System object™ computes sound pressure level measurements. The object returns measurements for:
frequency-weighted sound levels
fast or slow time-weighted sound levels
equivalent-continuous sound levels
peak sound levels
maximum sound levels
To implement SPL metering:
Create the
splMeter
object and set its properties.Call the object with arguments, as if it were a function.
To learn more about how System objects work, see What Are System Objects?
Creation
Description
SPL = splMeter
creates a System object, SPL
, that performs SPL metering.
SPL = splMeter(
sets each
property Name,Value
)Name
to the specified Value
. Unspecified
properties have default values.
Example: SPL =
splMeter('FrequencyWeighting','C-weighting','SampleRate',12000)
creates a System object, SPL
, that performs C-weighting and operates at 12
kHz.
Properties
Unless otherwise indicated, properties are nontunable, which means you cannot change their
values after calling the object. Objects lock when you call them, and the
release
function unlocks them.
If a property is tunable, you can change its value at any time.
For more information on changing property values, see System Design in MATLAB Using System Objects.
Bandwidth
— Width of analysis bands
'Full band'
(default) | '1 octave'
| '2/3 octave'
| '1/3 octave'
Width of analysis bands, specified as 'Full band'
, '1
octave'
, '2/3 octave'
, or '1/3
octave'
. If Bandwidth
is specified as 'Full
band'
, the SPL meter returns one set of measurements for the whole frequency
band. If Bandwidth
is specified as '1 octave'
,
'2/3 octave'
, or '1/3 octave'
, the SPL meter
returns one set of measurements per octave or fractional-octave band.
Tunable: No
Data Types: char
| string
FrequencyRange
— Frequency range of filter bank (Hz)
[22 22050]
(default) | two-element row vector of positive monotonically increasing values
Frequency range of the filter bank in Hz, specified as a two-element row vector of
positive monotonically increasing values. Frequency bands centered above
SampleRate
/2 are excluded.
Tunable: No
Dependencies
To enable this property, set Bandwidth
to '1
octave'
, '2/3 octave'
, or '1/3
octave'
.
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
OctaveFilterOrder
— Order of octave filter
2
(default) | even integer
Order of the octave filter, specified as an even integer.
Tunable: No
Dependencies
To enable this property, set Bandwidth
to '1
octave'
, '2/3 octave'
, or '1/3
octave'
.
Data Types: single
| double
FrequencyWeighting
— Frequency weighting applied to input
'A-weighting'
(default) | 'C-weighting'
| 'Z-weighting'
(no weighting)
Frequency weighting applied to input, specified as 'A-weighting'
,
'C-weighting'
, or 'Z-weighting'
, where
Z-weighting corresponds to no weighting. The frequency weighting is designed and
implemented using the weightingFilter
System object.
Tunable: No
Data Types: char
| string
TimeWeighting
— Time weighting (s)
'Fast'
(default) | 'Slow'
Time weighting, in seconds, for calculation of time-weighted sound level and maximum
time-weighted sound level, specified as 'Fast'
or
'Slow'
. The TimeWeighting
property is used to
specify the coefficient of a lowpass filter.
'Fast'
– 1/8'Slow'
– 1
Tunable: Yes
Data Types: char
| string
PressureReference
— Reference pressure for dB calculations (Pa)
2e-5
(default) | positive scalar
Reference pressure for dB calculations in Pa, specified as a positive scalar.
Tunable: Yes
Data Types: single
| double
TimeInterval
— Time interval for reporting level measurements (s)
1
(default) | positive scalar
Time interval, in seconds, to report equivalent-continuous, peak, and maximum time-weighted sound levels, specified as a positive scalar.
Tunable: No
Data Types: single
| double
CalibrationFactor
— Calibration factor multiplied by input
1 (default) | positive finite scalar or vector
Scalar (mono input) or vector (multichannel input) calibration factor multiplied by input.
To set the calibration factor using a reference tone, use calibrate
.
Tunable: No
Data Types: single
| double
SampleRate
— Input sample rate (Hz)
44100
(default) | positive scalar
Input sample rate in Hz, specified as a positive scalar.
Tunable: No
Data Types: single
| double
Usage
Description
Input Arguments
audioIn
— Audio input to SPL meter
column vector | matrix
Audio input to the SPL meter, specified as a column vector or matrix. The columns of the matrix are treated as independent audio channels.
Data Types: single
| double
Output Arguments
Lt
— Time-weighted sound level (dB)
column vector | matrix | 3-D array
Time-weighted sound level in dB, returned as a column vector, matrix, or 3-D array
the same type as audioIn
.
Size and interpretation of the outputs depend on what the Bandwidth property is set to:
'Full band'
(default) ––Lt
,Leq
,Lpeak
, andLmax
are returned as column vectors or matrices the same size asaudioIn
.'1 octave'
,'2/3 octave'
, or'1/3 octave'
––Lt
,Leq
,Lpeak
, andLmax
are returned as L-by-B-by-C arrays.L –– Number of rows in
audioIn
B –– Number of octave bands
C –– Number of columns in
audioIn
Data Types: single
| double
Leq
— Equivalent-continuous sound level (dB)
column vector | matrix | 3-D array
Equivalent-continuous sound level in dB, returned as a column vector, matrix, or
3-D array the same type as audioIn
.
Size and interpretation of the outputs depend on what the Bandwidth property is set to:
'Full band'
(default) ––Lt
,Leq
,Lpeak
, andLmax
are returned as column vectors or matrices the same size asaudioIn
.'1 octave'
,'2/3 octave'
, or'1/3 octave'
––Lt
,Leq
,Lpeak
, andLmax
are returned as L-by-B-by-C arrays.L –– Number of rows in
audioIn
B –– Number of octave bands
C –– Number of columns in
audioIn
Data Types: single
| double
Lpeak
— Peak sound level (dB)
column vector | matrix | 3-D array
Peak sound level in dB, returned as a column vector, matrix, or 3-D array the same
type as audioIn
.
Size and interpretation of the outputs depend on what the Bandwidth property is set to:
'Full band'
(default) ––Lt
,Leq
,Lpeak
, andLmax
are returned as column vectors or matrices the same size asaudioIn
.'1 octave'
,'2/3 octave'
, or'1/3 octave'
––Lt
,Leq
,Lpeak
, andLmax
are returned as L-by-B-by-C arrays.L –– Number of rows in
audioIn
B –– Number of octave bands
C –– Number of columns in
audioIn
Data Types: single
| double
Lmax
— Maximum time-weighted sound level (dB)
column vector | matrix | 3-D array
Maximum time-weighted sound level in dB, returned as a column vector, matrix, or
3-D array the same type as audioIn
.
Size and interpretation of the outputs depend on what the Bandwidth property is set to:
'Full band'
(default) ––Lt
,Leq
,Lpeak
, andLmax
are returned as column vectors or matrices the same size asaudioIn
.'1 octave'
,'2/3 octave'
, or'1/3 octave'
––Lt
,Leq
,Lpeak
, andLmax
are returned as L-by-B-by-C arrays.L –– Number of rows in
audioIn
B –– Number of octave bands
C –– Number of columns in
audioIn
Data Types: single
| double
Object Functions
To use an object function, specify the
System object as the first input argument. For
example, to release system resources of a System object named obj
, use
this syntax:
release(obj)
Specific to splMeter
calibrate | Calibrate meter using calibration tone with known level |
getCenterFrequencies | Center frequencies of filters |
Examples
Measure SPL of Audio Signal
Use the splMeter
System object™ to measure the A-weighted sound pressure level of a streaming audio signal. Specify a two second time-interval for reporting and a fast time-weighting. Visualize the SPL measurements using the timescope
object.
Create a dsp.AudioFileReader
object to read in an audio file frame by frame. Create an audioDeviceWriter
object to listen to the audio signal. Create a timescope
object to visualize SPL measurements. Create an splMeter
to measure the sound pressure level of the audio file. Use the default calibration factor of 1.
source = dsp.AudioFileReader("Ambiance-16-44p1-mono-12secs.wav"); fs = source.SampleRate; player = audioDeviceWriter(SampleRate=fs); scope = timescope(SampleRate=fs, ... TimeSpanSource="property",TimeSpan=3, ... YLimits=[20 110], ... ShowLegend=true,BufferLength=4*3*fs, ... ChannelNames=["Lt_AF","Leq_A","Lpeak_A","Lmax_AF"], ... Name="Sound Pressure Level Meter"); SPL = splMeter(TimeWeighting="Fast", ... FrequencyWeighting="A-weighting", ... SampleRate=fs, ... TimeInterval=2);
In an audio stream loop:
Read in the audio signal frame.
Play the audio signal to your output device.
Call the SPL meter to return the time-weighted, equivalent-continuous, peak, and maximum time-weighted sound levels in dB.
Display the sound levels using the scope.
As a best practice, release your objects once complete.
while ~isDone(source) x = source(); player(x); [Lt,Leq,Lpeak,Lmax] = SPL(x); scope([Lt,Leq,Lpeak,Lmax]) end release(source) release(player) release(SPL) release(scope)
Octave SPL Metering
The splMeter
enables you to monitor sound pressure level for octave and fractional-octave bands. In this example, you monitor the equivalent-continuous sound pressure level of 1/3-octave bands.
Create a dsp.AudioFileReader
object to read in an audio file frame by frame. Create an audioDeviceWriter
object so you can listen to the audio signal. Create an splMeter
to measure the octave sound pressure level of the audio file. Use the default calibration factor of 1. Create a dsp.ArrayPlot
object to visualize the equivalent-continuous SPL for each octave band.
source = dsp.AudioFileReader('JetAirplane-16-11p025-mono-16secs.wav'); fs = source.SampleRate; player = audioDeviceWriter('SampleRate',fs); SPL = splMeter( ... 'Bandwidth','1/3 octave', ... 'SampleRate',fs); centerFrequencies = getCenterFrequencies(SPL); scope = dsp.ArrayPlot(... 'XDataMode','Custom', ... 'CustomXData',centerFrequencies, ... 'XLabel','Octave Band Center Frequencies (Hz)', ... 'YLabel','Equivalent-Continuous Sound Level (dB)', ... 'YLimits',[20 90], ... 'ShowGrid',true, ... 'Name','Sound Pressure Level Meter');
In an audio stream loop:
Read in the audio signal frame.
Play the audio signal to your output device.
Call the SPL meter to return the equivalent-continuous sound pressure level in dB.
Display the sound levels using the scope. Update the scope only when the equivalent-continuous sound pressure level has changed.
As a best practice, release your objects once complete.
LeqPrevious = zeros(size(centerFrequencies)); while ~isDone(source) x = source(); player(x); [~,Leq] = SPL(x); for i = 1:size(Leq,1) if LeqPrevious ~= Leq(i,:) scope(Leq(i,:)') LeqPrevious = Leq(i,:); end end end release(source) release(player) release(SPL) release(scope)
Algorithms
Sound pressure level calculations follow the algorithms described in [1]. You can specify property values to conform to standards [2] and [3].
Calibration
To account for environmental and input device effects in SPL measurements, the audio input is multiplied by a calibration factor:
The CalibrationFactor
property can be set directly, or by using the
calibrate
function, which compares a known level with acquired data. The known level is determined
using a physical calibrator.
Frequency Weighting
A-, C-, or Z-frequency weighting is applied. The frequency weighting is implemented
using the weightingFilter
System object.
Analysis Bands
If you specify the Bandwidth
property as '1
octave'
, '2/3 octave'
or '1/3 octave'
,
then the SPL calculations are applied to each octave or fractional-octave band. These
analysis bands are determined after frequency weighting.
Time-Weighted Sound Level
Time-weighted sound level is defined as the ratio of the time-weighted root mean squared sound pressure to the reference sound pressure, converted to dB. That is,
h(y2) can be interpreted as the convolution of y2 with a filter with impulse response . y is the output of the frequency-weighting filter. The impulse response corresponds to a lowpass filter of the form . Using impulse invariance, the discrete filter can be interpreted as,
τ is specified by the time-weighting coefficient as 0.125 (if
TimeWeighting
is set to'Fast'
) or 1 (ifTimeWeighting
is set to'Slow'
).fs is the sample rate specified by the
SampleRate
property.
Equivalent-Continuous Sound Level
Equivalent-continuous sound level is also called time-average sound level. It is defined as the ratio of root mean squared sound pressure to the reference sound pressure, converted to dB. That is,
where
y is the output of the frequency-weighting filter.
po is the reference sound pressure, specified by the
PressureReference
property.
Peak Sound Level
Peak sound level is defined as the ratio of peak sound pressure to the reference sound pressure, converted to dB. That is,
where
y is the output of the frequency-weighting filter.
po is the reference sound pressure, specified by the
PressureReference
property.
Max Time-Weighted Sound Level
Maximum time-weighted sound level is defined as the greatest time-weighted sound level within a stated time interval.
References
[1] Harris, Cyril M. Handbook of Acoustical Measurements and Noise Control. 3rd ed. American Institute of Physics, 1998.
[2] International Electrotechnical Commission. Electroacoustics - Sound level meters - Part 1: Specifications. IEC 61672-1:2013.
[3] American National Standards Institute. ANSI S1.4: Specification for Sound Level Meters. 1983.
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Usage notes and limitations:
System Objects in MATLAB Code Generation (MATLAB Coder)
Version History
Introduced in R2018a
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