Overview

Low frequency noise generator

Discussion

Generates slowly varying random noise using by linearly interpolating between random values. The underlying random noise lies in the range [-1 +1). The module computes a new random value at the rate specified by .freq. If isSmoothed = 1, then linear interpolation is used between values. If isSmoothed = 0, then the output changes instantly effectively generating a square wave with constant period but random amplitudes.

Internally, the module uses a 32-bit linear congruential generator to generate random values. The initial seed of the random number generator is specified by .seed. If .fixCurrentSeed is 1, then the seed is fixed. This means that the prebuild function will not generate a new seed. By default, .fixCurrentSeed equals 0, and thus instances of the generator will produce different outputs.

Type Definition

typedef struct _ModuleRandiFract32
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    FLOAT32 freq;                                 // Rate at which random values are generated.
    INT32 isSmoothed;                             // Determines whether the random signal interpolates between random values (isSmoothed=1) or steps between random values (isSmoothed=0).
    fract32 slope;                                // Slope value for linear interpolation between random values.
    fract32 level;                                // The current value of the random signal.
    INT32 rate;                                   // Starting value for counter, dependent on freq.
    UINT32 seed;                                  // State of the random number generator.
    INT32 fixCurrentSeed;                         // Whether the prebuild function resets the seed or not. 0 = reset, 1 = no reset.
    INT32 counter;                                // Counter value is used in slewing between random values.
    fract32 oneOverRate;                          // Used in calculating the slope value.
} ModuleRandiFract32Class;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
freq	float	parameter	0	1000	0.01:24000	Hz
isSmoothed	int	parameter	0	1	0:1
slope	fract32	state	0	random value	Unrestricted
level	fract32	state	0	0	Unrestricted
rate	int	state	0	48	Unrestricted
seed	uint	state	0	random value	Unrestricted
fixCurrentSeed	int	parameter	0	0	0:1
counter	int	state	1	48	Unrestricted
oneOverRate	fract32	derived	1	0.02083	Unrestricted

Pins

Output Pins

Name: out

Description: audio output

Data type: fract32

MATLAB Usage

File Name: randi_fract32_module.m

 M=randi_fract32_module(NAME, SR, BLOCKSIZE)
 Creates a slowly varying random generator based on linear interpolation.
 This module has a single 1 channel output pin with controllable 
 frequency. The output of the module changes instantly when the 
 frequency is updated.  Fract32 version
 
 Arguments:
    NAME - name of the module.
    SR - sample rate.
    BLOCKSIZE - number of samples per output channel.