DerivativeFract32

Overview

Fixed point Discrete-time derivative

Discussion

Computes the derivative of a fixed-point (1.31 format) discrete-time signal. The derivative is defined as:

$y[n] = K/T * (x[n] - x[n-1])$ where T is the sample period and K is the optional gain parameter. The module sets the default starting value to x[-1] = 0.

The discrete derivative is similar to the continuous time derivative. For example, if the input is a sine wave at 1 kHz, then the output will be a cosine at 1 kHz scaled by 2*pi*1000.

The hidden internal array .lastValue stores the previous value x[n-1] between blocks. The length of the array is set by the prebuild function to the number of channels. The output format of the module is 18.14.

Type Definition

CODE

typedef struct _ModuleDerivativeFract32
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
    FLOAT32 gain;                                 // Additional gain.
    fract32 gainFract32;                          // Additional gain.
    fract32* lastValue;                           // Previous value x[n-1].
} ModuleDerivativeFract32Class;

Variables

Properties

Name	Type	Usage	isHidden	Default value	Range	Units
gain	float	parameter	0	1	-1:1	linear
gainFract32	fract32	derived	1	0.3662	Unrestricted
lastValue	fract32*	state	1	[1 x 1]	Unrestricted

Pins

Input Pins

Name: in

Description: Input signal

Data type: fract32

Channel range: Unrestricted

Block size range: Unrestricted

Sample rate range: Unrestricted

Complex support: Real

Output Pins

Name: out

Description: Output signal

Data type: fract32

MATLAB Usage

File Name: derivative_fract32_module.m

CODE

 M=derivative_fract32_module(NAME) 
 This module computes the derivative of the input signal.  Mathematically,
 this is:
   y[n] = 1/dt * (x[n] - x[n-1])
 where dt is the time step, dt = 1/SR.  The module has a multichannel
 input and computes the derivative per channel.  Arguments:
    NAME - name of the module.