Overview

Converts from linear units to decibels using a polynomial approximation

Discussion

Converts from linear units to decibels (db20) using a polynomial approximation. The input format is Q9.23 (values in the range +/- 128) and the output format is Q9.23 also (values in the range +/- 128). The function computes the absolute value of the input before computing the log. The output will always be in the range [48.16 -198.4738]. The results are accurate to within 8e-3 (in Q9.23).

For negative inputs the function takes the absolute value. An input of 0 returns -256.

Type Definition

typedef struct _ModuleDb20Fract32
{
    ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
} ModuleDb20Fract32Class;

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: db20_fract32_module.m

 M=db20_fract32_module(NAME)
 Creates an Audio Weaver module that computes the function 20*log10(abs(x))
 using a polynomial approximation.  The input and the output are Q9.23.
 Arguments:
    NAME - name of the module.