Overview

Fract32 Soft clip in Fract32

Discussion

The soft clipper uses a combination of piecewise linear and non-linear functions. Threshold sets the beginning of the knee. The maximum output is always -6*guardbit dB. The knee is shorter when the threshold is closer to max output.

Type Definition

typedef struct _ModuleSoftClipFract32
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    FLOAT32 threshold;                            // Transition point between linear response and knee.
    INT32 guardbit;                               // Linear threshold and max output are scaled by 2^(-guardbit) so output has 6*guardbit dB of headroom.
    fract32 th;                                   // Threshold in linear scale
    fract32* lastIn;                              // Array of last input sample, one per channel.
    fract32* lastOut;                             // Array of last output sample, one per channel.
    FLOAT32* currentGain;                         // Array of soft clipper gain, one per channel.
} ModuleSoftClipFract32Class;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
threshold	float	parameter	0	-4	-20:-0.5	dB
guardbit	int	parameter	0	4	0:8	linear
th	fract32	derived	1	0.03943	Unrestricted
lastIn	fract32*	state	1	[1 x 1]	Unrestricted	linear
lastOut	fract32*	state	1	[1 x 1]	Unrestricted	linear
currentGain	float*	state	0	[1 x 1]	-40:3	linear

Pins

Input Pins

Name: in

Description: audio input

Data type: fract32

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: audio output

Data type: fract32

MATLAB Usage

File Name: soft_clip_fract32_module.m

 M=soft_clip_fract32_module(NAME)
 Creates a soft clipper module for use in Audio Weaver.  The soft clipper
 is realized using a piecewise function.
 Arguments: clipping threshold in dB. When input signal is below the
 threshold, the gain of the soft clipper is 0 dB. 
 Then as the input signal increases, the output approaches max value of
 1.0. The soft clipper maintains the continuity of the piecewise
 compression function at the threshold point.
    NAME - name of the module.