100222-lecture6 - 1 EE522 Communications Theory Spring 2010...

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Unformatted text preview: 1 EE522 Communications Theory Spring 2010 Instructor: Hwang Soo Lee Lecture #6 – Speech Coding & Introduction to Signal-Space Approach to Modulation 2 Announcements ¡ HW #2 Due February 25 ¡ Project Proposals Due March 9 ¢ Some new project suggestions have been added to the projects section of the web page ¡ Handouts: ¢ Lecture #6 3 Source Coding/Data Compression ¡ Many digital data streams contain much redundant information. A digital picture file might contain many more 0’s than 1’s: 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 1 ¡ The operation of eliminating redundant data is called source coding or data compression. ¢ Unlike quantization, source coding can compress data without introducing distortion. ¡ Source coding is particularly important when bandwidth is expensive (e.g. FAX machines). ¡ Source coding is also important for storage of information on magnetic or optical media. 4 Source Coding Techniques ¡ Two main algorithms for source coding ¢ Huffman algorithm - for random data with known distribution ¢ Lempel-Ziv algorithm - for random data with unknown distribution • Used in most modern data compression routines ¡ For more detail on Source Coding and Quantization, take EE623 - Information Theory ¢ Reference: T. M. Cover and J. A. Thomas, Elements of Information Theory, Wiley, 1991. 5 Coding Techniques for Speech ¡ All speech coding techniques employ quantization. Many also employ additional properties of speech: ¢ Temporal Waveform Coding - attempt to represent time domain samples of speech waveform. ¢ Spectral Waveform Coding - attempt to represent spectral characteristics of speech waveform. ¢ Model-Based Encoding - attempt to replicate a model of the process by which speech was constructed. 6 Model-Based Speech Coding Techniques ¡ Linear Predictive Speech Coders (LPC) ¡ Speech is divided into frames of approximately 20 ms. ¡ Human speech is modeled as noise (air from the lungs) exciting a linear filter (throat, vocal cords, and mouth)....
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This note was uploaded on 11/23/2010 for the course EE EE522 taught by Professor Eeehwangsoo during the Spring '10 term at Korea Advanced Institute of Science and Technology.

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100222-lecture6 - 1 EE522 Communications Theory Spring 2010...

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