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Unformatted text preview: Purdue University: ECE438 - Digital Signal Processing with Applications 1 ECE438 - Laboratory 9: Speech Processing (Week 1) October 6, 2010 1 Introduction Speech is an acoustic waveform that conveys information from a speaker to a listener. Given the importance of this form of communication, it is no surprise that many applications of signal processing have been developed to manipulate speech signals. Almost all speech processing applications currently fall into three broad categories: speech recognition, speech synthesis, and speech coding. Speech recognition may be concerned with the identification of certain words, or with the identification of the speaker. Isolated word recognition algorithms attempt to identify individual words, such as in automated telephone services. Automatic speech recognition systems attempt to recognize continuous spoken language, possibly to convert into text within a word processor. These systems often incorporate grammatical cues to increase their accuracy. Speaker identification is mostly used in security applications, as a persons voice is much like a fingerprint. The objective in speech synthesis is to convert a string of text, or a sequence of words, into natural-sounding speech. One example is the Speech Plus synthesizer used by Stephen Hawking (although it unfortunately gives him an American accent). There are also similar systems which read text for the blind. Speech synthesis has also been used to aid scientists in learning about the mechanisms of human speech production, and thereby in the treatment of speech-related disorders. Speech coding is mainly concerned with exploiting certain redundancies of the speech signal, allowing it to be represented in a compressed form. Much of the research in speech compression has been motivated by the need to conserve bandwidth in communication sys- tems. For example, speech coding is used to reduce the bit rate in digital cellular systems. In this lab, we will describe some elementary properties of speech signals, introduce a tool known as the short-time discrete-time Fourier Transform , and show how it can be used to form a spectrogram . We will then use the spectrogram to estimate properties of speech waveforms. This is the first part of a two-week experiment. During the second week , we will study speech models and linear predictive coding. Questions or comments concerning this laboratory should be directed to Prof. Charles A. Bouman, School of Electrical and Computer Engineering, Purdue University, West Lafayette IN 47907; (765) 494- 0340; email@example.com Purdue University: ECE438 - Digital Signal Processing with Applications 2 2 Time Domain Analysis of Speech Signals Figure 1: The Human Speech Production System 2.1 Speech Production Speech consists of acoustic pressure waves created by the voluntary movements of anatom- ical structures in the human speech production system, shown in Figure 1. As the diaphragm forces air through the system, these structures are able to generate and shape a wide variety...
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