Introduction
Speech Coding
Speech coding has been a common area of research in signal processing since the introduction of
wire-based telephones. Numerous speech coding techniques have been thoroughly researched and
developed, spurned further by the advances in internet, technology and wireless communication.
Speech coding is a fundamental element of digital communications, continuously attracting
attention due to the increase of demands in telecommunication services and capabilities.
Applications of speech coders for signal processing purposes has improved at a very fast pace
throughout the years in order to allow it to take advantage of the increasing capabilities of
communication technology infrastructure and computer hardware.
This project focuses on the area of speech coding. This particular area has become a fundamental
necessity due to the bandwidth limitation of most signal transmission systems. Ideally in speech
coding, a digital representation of a speech signal is coded using a minimum number of bits to
achieve a satisfactory quality of the synthesized signal whilst maintaining a reasonable
computational complexity. Speech coding has two main applications: digital transmission and
storage of speech signals. In speech coding, our aim is to minimize the bit-rate while preserving a
certain quality of speech signal, or to improve speech quality at a certain bit rate.
Currently, there are various kinds of coders being implemented. This project focuses on the
design and implementation of a Code Excited Linear Predictive (CELP) coder. This Linear
Predictive Coding (LPC) method performs LP analysis of speech by extracting the LP parameters
and coefficients and employs a quantization method to search a codebook and compute the
excitation signal. The quantization of the LP parameters, play an important role in the
performance of the CELP coder. This project analyzes the performance of the CELP coder by
using various quantization methods such as Scalar, vector, DPCM and TSVQ to quantize the LP
parameters
.
Speech Production
Before proceeding with the handling of digitized speech, it is crucial to have a basic
understanding of how speech is produced. Speech is produced when the lungs force the direction
of airflow to pass through the larynx into the vocal tract. In normal speech production, the air that
is driven up from the lungs is passed through the glottis and vocal tract narrowing resulting in
periodic or aperiodic (noise) excitation.
Parts of the mouth’s anatomy, such as the jaw, tongue, lips, velum (soft palate) and nasal cavities,
act as resonant cavities. These cavities modify the excitation spectrum that is emitted as vibrating
sounds. Vowel sounds are produces with an open vocal tract with very little audible obstruction
restricting the movement of air. Consonant sounds are produced with a relatively closed vocal
tract, from temporary closure or narrowing of air passageway, resulting in high audible effect on
the flow of air.
4
我的内容管理
收起
我的收益 登录查看自己的收益
我的积分
登录查看自己的积分
我的C币
登录后查看C币余额
我的收藏 
我的下载 
下载帮助 
