Overview

Smooth Stereo Balance Module

Discussion

The Fractional Balance module smoothly scales left and right channels as specified by the balance parameter. The module has two multichannel input pins and two multichannel output pins. All dimensions of input and output pins are identical. The balance setting is automatically converted to target gains for left and right channels: gainL and gainR. gainL,R are computed from balance using the sine/cosine panning law: gainL = cos((1+balance)*pi/4), and gainR = sin((1+balance)*pi/4). Thus: full pan left-->gainL=1,gainR=0; full pan right-->gainL=0, gainR=1; balance=0, (centered) -->gainL=gainR=.707 . Internally currentGainL, currentGainR represent the instaneous smoothed gains applied to the left and right channels. currentGainL,R exponentially approach gainL,R with a time constant equal to smoothingTime. Note: we have only one time constant controlling both left and right channels. currentGainL,R also serve as the starting point of the module. If currentGainL,R = gainL,R then the module starts up in a converged state. If currentGain != gain for either left or right channels then currentGain will smoothly vary until the value of gain is reached.

Type Definition

typedef struct _ModuleBalanceFract32
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    FLOAT32 balance;                              // Left/Right Balance
    FLOAT32 smoothingTime;                        // Time constant of the smoothing process
    fract32 currentGainLFract32;                  // Instantaneous gain applied to left channel. This is also the starting gain of the left channel.
    fract32 currentGainRFract32;                  // Instantaneous gain applied to right channel. This is also the starting gain of the right channel.
    fract32 smoothingCoeff;                       // Smoothing coefficient
    fract32 gainLFract32;                         // Target gain left channel
    fract32 gainRFract32;                         // Target gain right channel
} ModuleBalanceFract32Class;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
balance	float	parameter	0	0	-1:1	linear
smoothingTime	float	parameter	0	10	0:1000	msec
currentGainLFract32	fract32	state	0	0.707	0:0.9999	linear
currentGainRFract32	fract32	state	0	0.707	0:0.9999	linear
smoothingCoeff	fract32	derived	1	0.002081	Unrestricted
gainLFract32	fract32	derived	1	0.7071	0:0.9999	linear
gainRFract32	fract32	derived	1	0.7071	0:0.9999	linear

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

Name: in2

Description: audio input

Data type: fract32

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out1

Description: audio output

Data type: fract32

Name: out2

Description: audio output

Data type: fract32

MATLAB Usage

File Name: balance_fract32_module.m

 M=balance_fract32_module(NAME)
 Creates a Fractional balance module for use in the 
 Audio Engine. The module has two multichannel inputs and two
 multichannel stereo outputs.  Each channel is scaled according to
 the value of a balance parameter.
 Arguments:
   NAME - name of the module.