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* Wireless * Audio Effects Processor

…. * Wireless * Audio Effects Processor. Lohith Kini Rahul Shroff Spyros Zoumpoulis April 30 th , 2007 6.111 Project Presentation. Our Model: AirTunes®. Audio input from source Compressed Wirelessly transmitted Decompressed Equalizer & Audio Effects. Decompression. Compression.

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* Wireless * Audio Effects Processor

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  1. …

  2. * Wireless* Audio Effects Processor Lohith Kini Rahul Shroff Spyros Zoumpoulis April 30th, 2007 6.111 Project Presentation

  3. Our Model: AirTunes® • Audio input from source • Compressed • Wirelessly transmitted • Decompressed • Equalizer & Audio Effects

  4. Decompression Compression IMDCT MDCT FSM SRAM SRAM Top Level Block Diagram IFFT AC97 Controller AC97 Codec Equalizer Transmission FFT Equalization FSM Reception

  5. Compression of Audio • MP3, MPEG-4, AAC • Modified Discrete Cosine Transform • Lapped : Map 2N discrete points into N discrete points MDCT

  6. WIRELESS MEMORY WE 10 18 8-pt. address Data_Out ac97_sdata_in ac97_synch Compression FSM AC97 Controller AC97 AC97 FSM ac97_sdata_out 16-pt. 18 Data WR ac97_bit_clock (global) FIFO RD Data_Out DA CLK 16-pt. 18 RFD 1D MDCT ND Data_Out RDY CLK Data Compression 8-pt. 18 RESET

  7. Wireless CC2420DBK RF Transceiver • CC2420 radio • 2.4 GHz frequency band • Atmel Atmega128L AVR microcontroller • 2x32 kBytes external RAM • PCB antenna • Joystick, buttons, LEDs (visual user application interface)

  8. Wireless Big Picture Block Memory (wireless) TX Control Unit Encoder (FEC) FPGA Packet Transmitter Packet Receiver Block Memory (wireless) Decoder (FEC) RX Control Unit FPGA

  9. Wireless Transmission Algorithm • Error Correction Algorithm • Forward Error Correction (FEC) • sender adds redundant data to its messages • allows receiver to detect errors • Reed Solomon Code • Key idea: • data is encoded as a polynomial • any k distinct points uniquely determine a polynomial of degree at most k-1 • Polynomial is then “encoded” by its evaluation at various points, and these values are what is actually sent • Transmission: some of these values may become corrupted • More than k points are actually sent • Receiver decodes the original data • Total number of m-bit symbols in the encoded block is n = 2m - 1 • Example: m = 8, Code Rate 223/255 • (In each block 223 symbols are formed from the encoder input and 32 parity symbols are added.) • Capable of correcting up to 16 symbols per block

  10. Equalization • Use FFT to convert audio signal into frequency spectrum • Add desired effects as required by the user • Take IFFT of resulting signal • Transmit processed audio to AC-97 output line

  11. Mult_re 18 IFFT Multiplier Module real_inv Mult_im LPF 18 8 ifft_enable to_ac97_data AC-97 Equalizer FFT_real 18 1024-pt. FFT 18 Bucketizer FFT_img 18 10 FFT_index Decompression Memory Audio Effects: The BIG Picture

  12. Questions?

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