Audioprocessor for Automobiles Using the TMS320C50 DSP

Ted Subonj

Presentation on SPRA302

CSE671 / Dr. S. Ganesan

Overview

Introduction

Goals

Hardware Components

Software Components

Conclusion

Introduction

Automobile Interior Space is Limited

Normal Echo is Not Present Inside an Automobile

Sound Inside a Car Can Lack a “Spacious” Quality

Introduction

Audio Characteristics Which Determine Space Size, as Perceived By The Ear Delay Between Original Signal and Echo Difference in Volume Between Original Signal

and Echo Sound Coming From Different Directions Ratio of Mono and Difference-Signal

Goals

Goal Is To Create A New Sense Of Space (Independent Of Actual Room)Four Signals Will Be Constructed From Two Stereo ChannelsOutput Signals Will Have A Variable Repetition Delay, Hence Simulating EchoOutput Signals Will Have A Variable Mono/Difference-Signal Mixing Ratio

Hardware Components

Processor Unit TMS320C50 DSP and Peripheral Components

Converter Unit Crystal CS4225 AD/DA Converter

Analog Unit (Converter Unit Support) Analog I/O Components Filters for Internal Reference Voltages

Hardware Components

I/O Interface 74AC138 I/O Decoder with 2 x 8-bit Inputs,

2 x 8-bit Outputs

Memory Interface 74AC138 Memory Decoder 32kWord x 16-bit RAM Memory Space

(Four 32k x 8-bit RAM Chips) 32k x 8-bit EEPROM Code Space

Hardware Components

UART-Serial InterfacePower Supply Two 5V Regulators

Processor and Converter Serial Interface Uses Both Processor Serial Ports for

Communication One Port for Audio Transmission in Both Directions One Port for Communication With User Interface

Hardware Components

LCD Display Hitachi LMO93XMLN 16 x 2 Character With Background LED Light

Keyboard 6 Closing Keys Using 1 Input Port Each

Software Components

Main Program User Interface Runs in the Background Read Keyboard Write to LCD and Converter Invoke the Active Menu Routine User Interface CPU Utilization: 1%

Software Components

Interrupts Four Interrupt Sources Receiving, Transmitting, and Processing of

Data Performed in Interrupt Subprograms

Calculation of Mono Signal and Channel-Difference Signal Mono Signal: Sum of Channels x Input Volume Difference Signal: Channel Difference x Vol.

Software Components

Echo Effects Step 1: Take Value from Circ Buffer Using

Echo Delay Pointer Step 2: Multiply By Feedback Volume Step 3: IIR Butterworth Low-Pass Filter Step 4: Sum the Input and Feedback Signal and

Restore it to the First Location of the Circular Buffer

Software Components

Calculate Channel Signals Get Mono and Channel-Difference Signals

From Circular Buffer Using Repetition Pointer Multiply By Their Respective Volume Sum the Values and Write Them to the

Channel’s Output Buffer

Software Components

User Interface Adjustable Parameters Main Volume (0 … 100%)

Attenuation for Converter’s Output Mono Echo (0 … 100m)

Mono Signal’s Delay Determines Difference Between Maximum Value and Repeat

Value in Circular Buffer Difference Signal Echo (0 … 100m)

Difference Signal’s Delay Determines Difference Between Maximum Value and Repeat

Value in Circular Buffer

Software Components

User Interface Adjustable Parameters (Cont’d) Mono Echo Feedback (0 … 100%)

Determines Volume of Echo’s Main Signal and Feedback

Difference Signal Echo Feedback (0 … 100%) Determines Volume of Echo’s Main Signal and

Feedback

Conclusion

The Audioprocessor Was Based on a TMS320C50 DSPThe Audio Interface Used a Crystal CS4225 Audio Converter ModuleThe User Interface Hardware Consisted of a Hitachi LMO93XMLN LCD and 6 KeysUser Interface and Signal Processing SW Were Designed and Implemented

Conclusion

Signal Processing Effects Were Developed and Tested Using the PC

Preprocessed Audio Data Was Played Using Two 16 Bit Sound Cards

The Hardware Was Built But Not Tested Due to PCB Delays