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.

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

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.