* Wireless* Audio Effects ProcessorOur Model: AirTunes®Top Level Block DiagramCompression of AudioWireless CC2420DBK RF Transceiver Wireless Big PictureWireless Transmission AlgorithmEqualizationAudio Effects: The BIG PictureQuestions?…* * WirelessWireless**Audio Effects Audio Effects ProcessorProcessorLohith KiniRahul ShroffSpyros ZoumpoulisApril 30th, 20076.111 Project PresentationOur Model: AirTunes®• Audio input from source• Compressed • Wirelessly transmitted• Decompressed• Equalizer & Audio EffectsTop Level Block DiagramTop Level Block DiagramAC97 ControllerAC97CodecDecompressionIMDCTSRAMCompressionMDCTSRAMFSMFSMTransmissionReceptionFFTIFFTEqualizerEqualizationCompression of AudioCompression of Audio••MP3, MPEGMP3, MPEG--4, AAC4, AAC––ModifiedModifiedDiscrete Cosine TransformDiscrete Cosine Transform••LappedLapped: Map : Map 2N2Ndiscrete points into discrete points into NNdiscrete discrete pointspointsMDCTAC97ac97_bit_clock(global)ac97_sdata_outac97_sdata_inac97_synchAC97 ControllerWRData18FIFOCompressionCLKRD Data_OutDADataNDCLKRESETRFDData_OutRDY1D MDCT18AC97 FSMCompressionFSMWIRELESS MEMORYWEaddressData_Out181816-pt.8-pt.8-pt.16-pt.10Wireless CC2420DBK RF Wireless CC2420DBK RF Transceiver Transceiver ••CC2420 radioCC2420 radio••2.4 GHz frequency band 2.4 GHz frequency band ••AtmelAtmelAtmega128L AVR microcontrollerAtmega128L AVR microcontroller••2x32 2x32 kByteskBytesexternal RAMexternal RAM••PCB antennaPCB antenna••Joystick, buttons, Joystick, buttons, LEDsLEDs(visual user application interface)(visual user application interface)Wireless Big PictureWireless Big PicturePacket TransmitterPacket TransmitterPacket ReceiverPacket ReceiverEncoder Encoder (FEC)(FEC)BlockBlockMemoryMemory(wireless)(wireless)TX Control UnitTX Control UnitDecoder Decoder (FEC)(FEC)RX Control UnitRX Control UnitBlockBlockMemoryMemory(wireless)(wireless)FPGAFPGAFPGAFPGAWireless 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 kkdistinct points distinct points uniquelyuniquelydetermine a polynomial of degree at most determine a polynomial of degree at most kk--11––Polynomial is then Polynomial is then ““encodedencoded””by its evaluation at various points, and these 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 kkpoints are actually sentpoints are actually sent––Receiver decodes the original dataReceiver decodes the original data––Total number of mTotal number of m--bit symbols in the encoded block is bit symbols in the encoded block is n = 2n = 2mm--11••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(In each block 223 symbols are formed from the encoder input and32 parity 32 parity symbols are added.) symbols are added.) ––Capable of correcting up to 16 symbols per blockCapable of correcting up to 16 symbols per blockEqualization• 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 lineDecompressionDecompressionMemoryMemory10241024--pt.pt.FFTFFTBucketizerBucketizerEqualizerEqualizerMultiplierMultiplierModuleModuleIFFTIFFTLPFLPFACAC--979718FFT_realFFT_imgFFT_index181810Mult_reMult_imifft_enable1818real_inv8to_ac97_dataAudio Effects: The BIG PictureAudio Effects: The BIG
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