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dsp.MovingRMS System object

Moving Root Mean Square


The dsp.MovingRMS System object™ computes the moving Root Mean Square (RMS) of the input signal along each channel, independently over time. The object uses either the sliding window method or the exponential weighting method to compute the moving RMS. In the sliding window method, a window of specified length is moved over the data, sample by sample, and the RMS is computed over the data in the window. In the exponential weighting method, the object squares the data samples, multiplies them with a set of weighting factors, and sums the weighed data. The object then computes the RMS by taking the square root of the sum. For more details on these methods, see Algorithms.

The object accepts multichannel inputs, that is, m-by-n size inputs, where m ≥ 1, and n > 1. The object also accepts variable-size inputs. Once the object is locked, you can change the size of each input channel. However, the number of channels cannot change. This object supports C and C++ code generation.

To compute the moving RMS of the input:

  1. Create a dsp.MovingRMS object and set the properties of the object.

  2. Call step to compute the moving RMS.


Alternatively, instead of using the step method to perform the operation defined by the System object, you can call the object with arguments, as if it were a function. For example, y = step(obj,x) and y = obj(x) perform equivalent operations.


movRMS = dsp.MovingRMS returns a moving RMS object, movRMS, using the default properties.

movRMS = dsp.MovingRMS(Len) sets the WindowLength property to Len.

movRMS = dsp.MovingRMS(Name,Value) specifies additional properties using Name,Value pairs. Unspecified properties have default values.


movRMS = dsp.MovingRMS('Method','Exponential weighting','ForgettingFactor',0.9);


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Moving RMS method, specified as 'Sliding window' or 'Exponential weighting'.

  • 'Sliding window' — A window of length specified by SpecifyWindowLength is moved over the input data along each channel. For every sample the window moves by, the object computes the RMS over the data in the window.

  • 'Exponential weighting' — The object multiplies the squares of the samples with a set of weighting factors. The magnitude of the weighting factors decreases exponentially as the age of the data increases, never reaching zero. To compute the RMS, the algorithm sums the weighted data, and takes a square root of the sum.

For more details on these methods, see Algorithms.

Flag to specify a window length, specified as a scalar Boolean.

  • true — The length of the sliding window is equal to the value you specify in the WindowLength property.

  • false — The length of the sliding window is infinite. In this mode, the RMS is computed using the current sample and all past samples.

This property applies when you set Method to 'Sliding window'.

Length of the sliding window, specified as a positive scalar integer. This property applies when you set Method to 'Sliding window' and SpecifyWindowLength to true.

Exponential weighting factor, specified as a positive real scalar in the range (0,1]. This property applies when you set Method to 'Exponential weighting'.

A forgetting factor of 0.9 gives more weight to the older data than does a forgetting factor of 0.1. A forgetting factor of 1.0 indicates infinite memory. All the past samples are given an equal weight.

This property is tunable. You can change its value even when the object is locked.


resetReset internal states of System object
stepMoving RMS of input signal
Common to All System Objects

Create System object with same property values


Expected number of inputs to a System object


Expected number of outputs of a System object


Check locked states of a System object (logical)


Allow System object property value changes


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Compute the moving RMS of a noisy square wave signal with varying amplitude using the dsp.MovingRMS object.


Set up movrmsWin and movrmsExp objects. movrmsWin uses the sliding window method with a window length of 20. movrmsExp uses the exponential weighting method with a forgetting factor of 0.995. Create a time scope for viewing the output.

FrameLength = 10;
Fs = 100;
movrmsWin = dsp.MovingRMS(20);
movrmsExp = dsp.MovingRMS('Method','Exponential weighting',...
scope  = dsp.TimeScope('SampleRate',Fs,...
    'YLimits',[-1.0 5.5]);
title = 'Sliding Window RMS (blue) and Exponentially Weighted RMS (red)';
scope.Title = title;

Compute the RMS

Generate a noisy square wave signal. Vary the amplitude of the square wave after a given number of frames. Apply the sliding window method and the exponential weighting method on this signal. View the output on the time scope.

count = 1;
Vect = [1/8 1/2 1 2 3 4];
index = 1;
for index = 1:length(Vect)
    V = Vect(index);
    for i = 1:160
        x = V + 0.1 * randn(FrameLength,1);
        y1 = movrmsWin(x);
        y2 = movrmsExp(x);


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[1] Bodenham, Dean. “Adaptive Filtering and Change Detection for Streaming Data.” PH.D. Thesis. Imperial College, London, 2012.

Extended Capabilities

Introduced in R2016b

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