1. Audioprocessor for Automobiles Using the TMS320C50 DSP Ted Subonj Presentation on SPRA302 CSE671 / Dr. S. Ganesan

2. Overview Introduction Goals Hardware Components Software Components Conclusion

3. Introduction Automobile Interior Space is Limited Normal Echo is Not Present Inside an Automobile Sound Inside a Car Can Lack a “Spacious” Quality

4. 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

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

6. 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

7. 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

8. Hardware Components UART-Serial Interface Power 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

9. Hardware Components LCD Display Hitachi LMO93XMLN 16 x 2 Character With Background LED Light Keyboard 6 Closing Keys Using 1 Input Port Each

10. 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%

11. 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.

12. 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

13. 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

14. 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

15. 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

16. Conclusion The Audioprocessor Was Based on a TMS320C50 DSP The Audio Interface Used a Crystal CS4225 Audio Converter Module The User Interface Hardware Consisted of a Hitachi LMO93XMLN LCD and 6 Keys User Interface and Signal Processing SW Were Designed and Implemented

17. 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