RMSN

Overview

Multichannel RMS detector with built-in smoothing

Discussion

This module calculates the smoothed RMS value of the input signal on a block-by-block basis. The input pin can have an arbitrary number of interleaved channels and the RMS calculation occurs on a channel by channel basis. The output pin has a multiple channels all with a blockSize of 1.

The following algorithm is used internally. For each channel, the sum of the square of all input data is computed (the energy). Next, the energy is divided by the number of samples to yield the average energy. The average energy then passes through a first order lowpass filter with a specified integration time (the smoothingTime). Finally, the square root of the filter output is computed and this serves as the output of the module.

Module Pack

Standard

ClassID

classID = 218

Type Definition

typedef struct _ModuleRMSN
{
ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
FLOAT32 smoothingTime;                        // Time interval over which to smooth the measurement.
FLOAT32 a1;                                   // a1 coefficient of 1st order smoothing filter.
FLOAT32 b0;                                   // b0 coefficient of 1st order smoothing filter.
FLOAT32* energy;                              // Array of squared energy values, one per channel.
} ModuleRMSNClass;

Variables

Properties

Name	Type	Usage	isHidden	Default Value	Range	Units
smoothingTime	float	parameter	0	1000	0:10000	msec
a1	float	derived	1	-0.9958	Unrestricted
b0	float	derived	1	0.00418	Unrestricted
energy	float*	state	1	[1 x 1]	Unrestricted

Pins

Input Pins


Name	in
Description	Audio input
Data type	float
Channel range	Unrestricted
Block size range	Unrestricted
Sample rate range	Unrestricted
Complex support	Real

Output Pins


Name	out
Description	Filtered RMS output
Data Type	float

Matlab Usage

File Name: rmsn_module.m 
 M = rmsn_module(NAME) 
 Multichannel RMS detector with a separate value computed per input 
 channel.  The module has a single multichannel input (numChan x blockSize) 
 and a single multichannel output (1 x blockSize).  The module has a 
 configurable smoothing time.  Arguments: 
    NAME - name of the module.