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(8.D.2.4) Db20Fract32

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.

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