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.*conj(u))/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 y_ij containing the RMS value of element u_ij over all inputs since the last reset. For frame-based inputs, the output is a frame-based M-by-N matrix with each element y_ij containing the RMS value of the jth column over all inputs since the last reset, up to and including element u_ij 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.

Resetting the Running RMS.   The block resets the running RMS whenever a reset event is detected at the optional Rst port. The reset signal rate must be a positive integer multiple of the rate of the data signal input.

When the block is reset 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.

The reset event is specified by the Reset port parameter, and can be one of the following:

• None disables the Rst port.
• Rising edge -- Triggers a reset operation when the Rst input does one of the following:
• Rises from a negative value to a positive value or zero
• Rises from zero to a positive value, where the rise is not a continuation of a rise from a negative value to zero (see the following figure)
  
  
• Falling edge -- Triggers a reset operation when the Rst input does one of the following:
• Falls from a positive value to a negative value or zero
• Falls from zero to a negative value, where the fall is not a continuation of a fall from a positive value to zero (see the following figure)
  
  
• Either edge -- Triggers a reset operation when the Rst input is a Rising edge or Falling edge (as described above).
• Non-zero sample -- Triggers a reset operation at each sample time that the Rst input is not zero.

Note    When running simulations in the Simulink MultiTasking mode, sample-based reset signals have a one-sample latency, and frame-based reset signals have one frame of latency. Thus, there is a one-sample or one-frame delay between the time the block detects a reset event, and when it applies the reset. For more information on latency and the Simulink tasking modes, see Excess Algorithmic Delay (Tasking Latency) and the topic on the Simulation Parameters dialog box in the Simulink documentation.

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

Determines the reset event that causes the block to reset the running RMS. The reset signal rate must be a positive integer multiple of the rate of the data signal input. This parameter is enabled only when you set the Running RMS parameter. For more information, see Resetting the Running RMS.

Supported Data Types

• Double-precision floating point
• Single-precision floating point
• Boolean -- The block accepts Boolean inputs to the Rst port.

To learn how to convert to the above data types in MATLAB and Simulink, see Supported Data Types and How to Convert to Them.

See Also

Mean	DSP Blockset
Variance	DSP Blockset

Also see Statistics for a list of all the blocks in the Statistics library.

RLS Adaptive Filter

Sample and Hold