DSP Blockset

RMS

Compute the root-mean-square (RMS) value of an input or sequence of inputs.

Library

Statistics

Description

The RMS block computes the RMS value of each column in the input, or tracks the RMS value of a sequence of inputs over a period of time. The Running RMS parameter selects between basic operation and running operation.

Basic Operation

When the Running RMS check box is not selected, the block computes the RMS value of each column in M-by-N input matrix u independently at each sample time.

y = sqrt(sum(u.^2)/size(u,1))     % Equivalent MATLAB code

For convenience, length-M 1-D vector inputs and sample-based length-M row vector inputs are both treated as M-by-1 column vectors.

The output at each sample time, y, is a 1-by-N vector containing the RMS value for each column in u. The RMS value of the jth column is

The frame status of the output is the same as that of the input.

Running Operation

When the Running RMS check box is selected, the block tracks the RMS value of each channel in a time-sequence of M-by-N inputs. For sample-based inputs, the output is a sample-based M-by-N matrix with each element yij containing the RMS value of element uij over all inputs since the last reset. For frame-based inputs, the output is a frame-based M-by-N matrix with each element yij containing the RMS value of the jth column over all inputs since the last reset, up to and including element uij of the current input.

If the Reset port parameter is set to Non-zero sample, the optional Rst port is enabled and the block resets the running RMS when the scalar input at the Rst port is nonzero. (The Rst port can be disabled by setting the Reset port parameter to None.) For sample-based inputs, the running RMS for each channel is initialized to the value in the corresponding channel of the current input. For frame-based inputs, the running RMS for each channel is initialized to the earliest value in each channel of the current input.

As in basic operation, length-M 1-D vector inputs and sample-based length-M row vector inputs are both treated as M-by-1 column vectors.

Example

The RMS block in the model below calculates the running RMS of a frame-based 3-by-2 (two-channel) matrix input, u. The running RMS is reset at t=2 by an impulse to the block's Rst port.

The RMS block has the following settings:

• Running RMS =
• Reset port = Non-zero sample

The Signal From Workspace block has the following settings:

• Signal = u
• Sample time = 1/3
• Samples per frame = 3

where

u = [6 1 3 -7 2 5 8 0 -1 -3 2 1;1 3 9 2 4 1 6 2 5 0 4 17]'

The Discrete Impulse block has the following settings:

• Delay (samples) = 2
• Sample time = 1
• Samples per frame = 1

The block's operation is shown in the figure below.

Dialog Box

Running RMS

Enables running operation when selected.

Reset port

Enables the Rst input port when set to Non-zero sample, and disables the Rst input port when set to None.

See Also

Mean	DSP Blockset
Variance	DSP Blockset

RLS Adaptive Filter

Sample and Hold