Overview

Linear multichannel smoothly varying dB scaler

Discussion

The Scaler DB Smoothed module smoothly scales multichannel input data by a single gain value specified in dB, (gainDB). The module has i multichannel input pin and one output pin of the same dimensions as the input pin. gainDB is automatically converted to a linear value: gain. Changes to the gain parameter are exponentially smoothed (first order IIR) at the sample rate, with the time constant determined by the smoothingTime parameter. This module is controlled by varying the gainDB variable. gainDB is then converted to gain. Internally, currentGain represents the instantaneous smoothed gain that is applied. currentGain exponentially approaches gain with a time constant equal to smoothingTime. currentGain also serves as the starting point of the module. If currentGain = gain then the module starts up in a converged state. If currentGain != gain then the module will smoothly vary the gain at startup.

Type Definition

typedef struct _ModuleScalerDBSmoothedFract32
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    FLOAT32 smoothingTime;                        // Time constant of the smoothing process
    FLOAT32 gainDB;                               // Target gain in DB
    fract32 targetGain;                           // Desired (or target) of the fractional portion of the overall scaling. This is also the starting gain of the module.
    fract32 currentGain;                          // Instantaneous gain applied by the module. This is also the starting gain of the module.
    fract32 smoothingCoeff;                       // Smoothing coefficient
    INT32 postShift;                              // Number of bits to shift after the fractional multiply. This is based on gain.range.
    FLOAT32 twoPowMinusPostShift;                 // 2^(-postShift). Used by to streamline the operation of the set function
} ModuleScalerDBSmoothedFract32Class;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
smoothingTime	float	parameter	0	10	0:1000	msec
gainDB	float	parameter	0	0	-40:0.1:20	dB
targetGain	fract32	derived	1	0.0625	Unrestricted
currentGain	fract32	state	1	0.0625	Unrestricted
smoothingCoeff	fract32	derived	1	0.002081	Unrestricted
postShift	int	derived	1	4	Unrestricted
twoPowMinusPostShift	float	derived	1	0.0625	Unrestricted

Pins

Input Pins

Name: in1

Description: audio input

Data type: fract32

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real and Complex

Output Pins

Name: out1

Description: audio output

Data type: fract32

MATLAB Usage

File Name: scaler_db_smoothed_fract32_module.m

 M=scaler_db_smoothed_fract32_module(NAME, NUMPINS)
 Creates a smoothed dB scaler for use in the
 Audio Weaver. The module has a single multichannel
 input and scales all channels by the same value.
 Arguments:
    NAME - name of the module.
    NUMPINS - number of pins, optional (default=1)