…. * wireless * audio effects processor lohith kini rahul shroff spyros zoumpoulis april 30 th,...
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* * WirelessWireless** Audio Effects Audio Effects ProcessorProcessor
Lohith KiniRahul Shroff
Spyros Zoumpoulis
April 30th, 20076.111 Project Presentation
Our Model: AirTunes®
• Audio input from source
• Compressed • Wirelessly transmitted• Decompressed• Equalizer & Audio
Effects
Top Level Block DiagramTop Level Block Diagram
AC97 Controller
AC97Codec
Decompression
IMDCTSRAM
Compression
MDCT
SRAM
FSM
FSM
Transmission
Reception
FFT
IFFT
Equalizer
Equalization
Compression of AudioCompression of Audio
• MP3, MPEG-4, AACMP3, MPEG-4, AAC– ModifiedModified Discrete Cosine Transform Discrete Cosine Transform
• LappedLapped : Map : Map 2N2N discrete points into discrete points into NN discrete discrete pointspoints
MDCT
AC97
ac97_bit_clock(global)
ac97_sdata_out
ac97_sdata_inac97_synch
AC97 Controller
WR Data
18
FIFO
Compression
CLKRD Data_Out
DA
DataND
CLK
RESET
RFDData_Out RDY
1D MDCT
18
AC97 FSM
CompressionFSM
WIRELESS MEMORY
WEaddress
Data_Out
18
18
16-pt.
8-pt.
8-pt.
16-pt.
10
Wireless CC2420DBK RF Wireless CC2420DBK RF Transceiver Transceiver
• CC2420 radioCC2420 radio• 2.4 GHz frequency band 2.4 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)
Wireless Big PictureWireless Big Picture
Packet TransmitterPacket Transmitter
Packet ReceiverPacket Receiver
Encoder Encoder (FEC)(FEC)
BlockBlockMemoryMemory(wireless)(wireless)
TX Control UnitTX Control Unit
Decoder Decoder (FEC)(FEC)
RX Control UnitRX Control Unit
BlockBlockMemoryMemory(wireless)(wireless)
FPGAFPGA
FPGAFPGA
Wireless Transmission AlgorithmWireless Transmission Algorithm
• Error Correction AlgorithmError Correction Algorithm– Forward Error Correction (FEC)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:Key idea:
• data is encoded as a polynomialdata is encoded as a polynomial• any any kk distinct points distinct points uniquelyuniquely determine a polynomial of degree at most determine a polynomial of degree at most kk-1-1
– Polynomial is then “encoded” by its evaluation at various points, and these Polynomial is then “encoded” by its evaluation at various points, and these values are what is actually sentvalues are what is actually sent
– Transmission: some of these values may become corrupted Transmission: some of these values may become corrupted – More than More than kk points are actually sent points are actually sent– Receiver decodes the original dataReceiver decodes the original data– Total number of m-bit symbols in the encoded block is Total number of m-bit symbols in the encoded block is n = 2n = 2mm - 1 - 1
• Example: m = 8, Code Rate 223/255 Example: m = 8, Code Rate 223/255 – (In each block 223 symbols are formed from the encoder input and 32 parity (In each block 223 symbols are formed from the encoder input and 32 parity
symbols are added.) symbols are added.) – Capable of correcting up to 16 symbols per blockCapable of correcting up to 16 symbols per block
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
DecompressionDecompressionMemoryMemory
1024-pt.1024-pt.FFTFFT
BucketizerBucketizer
EqualizerEqualizer
MultiplierMultiplierModuleModuleIFFTIFFTLPFLPF
AC-97AC-97
18
FFT_real
FFT_img
FFT_index
18
18
10
Mult_re
Mult_im
ifft_enable
18
18
real_inv
8
to_ac97_data
Audio Effects: The BIG PictureAudio Effects: The BIG Picture