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

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

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

5. Compression of Audio MP3, MPEG-4, AACMP3, MPEG-4, AAC –Modified Discrete Cosine Transform Lapped : Map 2N discrete points into N discrete pointsLapped : Map 2N discrete points into N discrete points MDCT

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

7. Wireless CC2420DBK RF Transceiver CC2420 radioCC2420 radio 2.4 GHz frequency band2.4 GHz frequency band Atmel Atmega128L AVR microcontrollerAtmel Atmega128L AVR microcontroller 2x32 kBytes external RAM2x32 kBytes external RAM PCB antennaPCB antenna Joystick, buttons, LEDs (visual user application interface)Joystick, buttons, LEDs (visual user application interface)

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

9. Wireless Transmission Algorithm Error Correction AlgorithmError Correction Algorithm –Forward Error Correction (FEC) sender adds redundant data to its messagessender adds redundant data to its messages allows receiver to detect errorsallows receiver to detect errors Reed Solomon CodeReed Solomon Code –Key idea: data is encoded as a polynomialdata is encoded as a polynomial any k distinct points uniquely determine a polynomial of degree at most k-1any 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 = 2 m - 1 Example: m = 8, Code Rate 223/255Example: 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. DecompressionMemory 1024-pt.FFT Bucketizer Equalizer MultiplierModuleIFFT LPF AC-97 18 FFT_real FFT_img FFT_index 18 10 Mult_re Mult_im ifft_enable 18 real_inv 8 to_ac97_data Audio Effects: The BIG Picture

12. Questions?