1 Introduction to Speech Coding What, Why, Where & How (First Part) By Allam Mousa Department of Telecommunication Engineering An Najah University SP_2_Coding_1of2

2 Contents   What is speech coding   Applications   Types of coding   Practical examples of speech coders   Some properties of speech coders   Quantization   Some speech coder standards   Some Speech Properties   Coding Principles SP_2_Coding_1of2

3 What is Speech Coding ?   Speech coding is concerned with compact digital representations of speech signals for efficient transmission or storage.   The objective is to represent a signal with a minimum number of bits while maintaining perceptual quality.   Current applications for speech and audio coding algorithms include cellular and personal communications networks (PCNs), teleconferencing, multi- media systems, and secure communications.   speech coding systems is to transmit speech with the highest possible quality using the least possible channel capacity.   To save bandwidth in telecoms applications and to reduce memory storage requirements. SP_2_Coding_1of2

Why Speech Coding?  speech coding systems is to transmit speech with the highest possible quality using the least possible channel capacity.  To save bandwidth in telecoms applications and to reduce memory storage requirements. 4SP_2_Coding_1of2

5 Applications of Speech Coding   Wire line Telephony   Videoconferencing   Digital Cellular   IP Telephony   Voice Mail   Speech Storage World wide growth in communications World wide growth in communications Need for new multimedia applications Need for new multimedia applications Advances in VLSI Advances in VLSI SP_2_Coding_1of2

Speech Coding Hierarchy: 6SP_2_Coding_1of2

7 Standardization  International Telecommunication Union (ITU)  European Telecommunication Standards Institute (ETSI)  International Standards Organization (ISO)  Telecommunication Industry Association (TIA)  R&D Center for Radio systems (RCR) SP_2_Coding_1of2

Characteristic of Speech Signals: Characteristic of Speech Signals: 1-Probability Density Function(PDF): the pdf of speech signal is in general characterized by a very high probability of near zero amplitudes, a significant probability of very high amplitudes the pdf of speech signal is in general characterized by a very high probability of near zero amplitudes, a significant probability of very high amplitudes 8SP_2_Coding_1of2

Characteristic of Speech Signals: Characteristic of Speech Signals: 2-Autocorrelation Function (ACF): The ACF gives a quantitative measure of the closeness or similarity between samples of a speech signal as a function of their time separation. The ACF gives a quantitative measure of the closeness or similarity between samples of a speech signal as a function of their time separation. 9SP_2_Coding_1of2

Characteristic of Speech Signals: 3-Power Spectral Function (PSD): The nonflat characteristic of the power spectral density of speech makes it possible to obtain significant compression by coding speech in the frequency domain. 10SP_2_Coding_1of2