Overview

General purpose multiplexor

Discussion

This module has a variable number of input pins and routes (or copies) one of these pins to the output pin, while smoothly varying the multiplexor module with fade time between input pin transitions.

This module has built in smoothing to prevent audible clicks when transitioning between input pins. The smoothing is performed using a first order smoother and the variable smoothingTime controls the transition rate. It takes about 3 x smoothingTime for the complete transition to occur.

An optional control pin (Ctrl) is provided (enabled under module Arguments using isControl = true). The first sample value of the control pin is used as the index for the multiplexor input pins; all other values are ignored. The control pin contains an integer value in the range 0 to N-1, where N is the number of audio inputs. If the control value is outside of the allowable range it is clipped to max index (N-1).

Only when the control pin is disabled (isControl = false) the index for the multiplexor input pins can be selected from the Module Inspector (Double clicking on the Module on the designer canvas)

Each audio input pin must have the same number of channels and block size.

The module can also be configured to output zeros between transitions. The variable fadeTime specifies the silence period, in msec, when transitions occur.

Type Definition

typedef struct _ModuleMultiplexorV2
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    INT32 index;                                  // Specifies which input pin to route to the output. The index is zero based.
    FLOAT32 smoothingTime;                        // Time constant of the smoothing process
    FLOAT32 fadeTime;                             // Silence time in crossfade
    INT32 isControl;                              // Indicates if the index is controlled by an external signal
    FLOAT32 smoothingCoeff;                       // Smoothing coefficient
    FLOAT32 oldSrcGain;                           // Instanteous gain being applied to the old source. This is an internal variable used in the smoothing process
    FLOAT32 newSrcGain;                           // Instanteous gain being applied to the new source. This is an internal variable used in the smoothing process
    INT32 fadeState;                              // State variable for determining when to transitioning between inputs
    INT32 fadeStateInit;                          // Derived from fadeTime, determines number of blocks to wait before switching input pins
    INT32 oldIndex;                               // This is the index that is currently being used
    INT32 newIndex;                               // This is the index being transitioned to
} ModuleMultiplexorV2Class;

Variables

Properties

Pins

Input Pins

Name: Ctrl

Description: Input pin control signal

Data type: int

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Name: in1

Description: Input signal

Data type: float

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real and Complex

Name: in2

Description: Input signal

Data type: float

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real and Complex

Name: in3

Description: Input signal

Data type: float

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real and Complex

Output Pins

Name: out

Description: Output signal

Data type: float

MATLAB Usage

File Name: multiplexor_v2_module.m

 M = multiplexor_v2_module(NAME, ISCONTROL, NUMINPINS)
 Creates a multiplexor module that seamlessly switches between inputs.
 The module has multiple input pins and switches from one input to another.
 The optional control pin is the first pin (when enabled) and determines
 which of N inputs is selected. The input pin is an integer value in the
 range 0 to N-1.
 Arguments:
    NAME - name of the module.
    ISCONTROL - enables or disables the control pin
    NUMINPINS - number of input pins.
 All input pins must have the same block size and number of channels.
 Note, this verson implements an optional smooth crossfade between inputs.