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Lecture 2_winter_2012_6tp

Lecture 2_winter_2012_6tp - What is DSP Input Signal...

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1 1 Digital Speech Processing— Lecture 2 Review of DSP Fundamentals 2 What is DSP? Analog-to- Digital Conversion Computer Input Signal Output Signal Digital-to- Analog Conversion Digital Method to represent a quantity, a phenomenon or an event Why digital? Signal What is a signal? something (e.g., a sound, gesture, or object) that carries information a detectable physical quantity (e.g., a voltage, current, or magnetic field strength) by which messages or information can be transmitted What are we interested in, particularly when the signal is speech? Processing What kind of processing do we need and encounter almost everyday? Special effects? 3 Common Forms of Computing Text processing – handling of text, tables, basic arithmetic and logic operations (i.e., calculator functions) Word processing Language processing Spreadsheet processing Presentation processing Signal Processing – a more general form of information processing, including handling of speech, audio, image, video, etc. Filtering/spectral analysis Analysis, recognition, synthesis and coding of real world signals Detection and estimation of signals in the presence of noise or interference 4 Advantages of Digital Representations Permanence and robustness of signal representations; zero- distortion reproduction may be achievable Advanced IC technology works well for digital systems Virtually infinite flexibility with digital systems – Multi-functionality – Multi-input/multi-output Indispensable in telecommunications which is virtually all digital at the present time Signal Processor Input Signal Output Signal A-to-D Converter D-to-A Converter 5 Digital Processing of Analog Signals A-to-D conversion: bandwidth control, sampling and quantization Computational processing: implemented on computers or ASICs with finite-precision arithmetic basic numerical processing: add, subtract, multiply (scaling, amplification, attenuation), mute, … algorithmic numerical processing: convolution or linear filtering, non-linear filtering (e.g., median filtering), difference equations, DFT, inverse filtering, MAX/MIN, … D-to-A conversion: re-quantification* and filtering (or interpolation) for reconstruction x c ( t ) x [ n ] y [ n ] y c ( t ) A-to-D Computer D-to-A 6 Discrete-Time Signals { [ ]}, ( ), , [ ] ( ), A sequence of numbers Mathematical representation: Sampled from an analog signal, at time is called the and its recipr a a x x n n x t t nT x n x nT n T = − ∞ < < ∞ = = − ∞ < < ∞ sampling period, ± ± ± ± 1/ , 8000 1/ 8000 125 sec 10000 1/10000 100 sec 16000 1/16000 62.5 sec 20000 1/ 20000 50 sec ocal, is called the Hz Hz Hz Hz S S S S S F T F T F T F T F T μ μ μ μ = = = = = = = = = = = = = sampling frequency
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2 Speech Waveform Display 7 plot( ); stem( ); 8 Varying Sampling Rates Fs=8000 Hz Fs=6000 Hz Fs=10000 Hz Varying Sampling Rates 9 Fs=8000 Hz Fs=6000 Hz Fs=10000 Hz Quantization in out 0.3 0.9 1.5 2.1 2.4 1.8 1.2 0.6 7 6 5 4 3 2 1 0 A 3-bit uniform quantizer Quantization: Transforming a continuously- valued input into a representation that assumes
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