Overview

Subband RMS detector

Discussion

Compute the smoothed RMS value of frequency domain data on a subband-by-subband basis The module accepts real or complex inputs and has a separate state variable per subband. The module accepts an arbitrary blockSize and numChannels.

The module first computes the energy of the input, passes this through a first order smoother, and then compute the square root. The smoothing time is configured in milliseconds and a time of 0 milliseconds is allowable. When the smoothing time is 0 milliseconds, the output equals the magnitude of the input. The size of the output pin matches the size of the input pin. The only difference is that the output pin is always real data.

When bypassed the module computes the absolute value of the input; no smoothing occurs. For real data, the output is just fabs(in). For complex data, the square root of the magnitude squared is returned.

Type Definition

typedef struct _ModuleSbRMS
{
    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* yNm1;                                // Delayed output vector.
} ModuleSbRMSClass;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
smoothingTime	float	parameter	0	1000	0:10000	msec
a1	float	derived	1	-0.9999	Unrestricted
b0	float	derived	1	0.0001309	Unrestricted
yNm1	float*	state	1	[32 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 and Complex

Output Pins

Name: out

Description: audio output

Data type: float

MATLAB Usage

File Name: sb_rms_module.m

 M=sb_rms_module(NAME)
 Subband RMS detector in which the RMS value of each subband is 
 separately computed.  Each subband has its own state variables
 and there is a single smoothing time across all bands.
 % Arguments:
    NAME - name of the module.
 Copyright 2011.  DSP Concepts, Inc.  All Rights Reserved.