音频信息处理技术

1、 音频信息处理技术音频信息处理技术l1 Basics of Digtial Audio 声学基础知识l2 Digitization of Sound 音频信号数字化l3 Audio signal compression coding音频信号压缩编码l4 Coding standard of Speech compression 语音压缩编码标准l5 Multimedia audio signal file format多媒体音频信号文件格式 made by fangshuai&lijian 8#319 1 Basics of Digtial Audio 声学基础知识声学基础知识l1.1

2、 Audio signal characteristics音频信号特征 1、The time domain characteristics of voice signal声音信号的时域特征 This feature suggests people hear the voice of the process from production to the end of the.该特征说明人们听到的声音从产生到结束的过程。 This process can be divided into three stages: initiation, stable and end.这个过程大致可分为三个阶段：起

3、始、稳定和结束。 2、The frequency characteristics of sound signal声音信号的频域特征 lThe frequency of the acoustic wave声波频率 20Hz20kHz （Hertz）lSound pressure:The sound intensity of feeling 1kHz210-5Pa 1.2 The auditory characteristicsl1、Loudness：The human ear to sound intensity of feeling。l2、Masking effect： A voice wil

4、l influence the existence of people hearing ability of other sounds, make a sound in the auditory masking another sound。 2 音频信号数字化音频信号数字化 The process of digital audio signal is analog audio signal into a discrete sequence of a finite representation of numbers, digital audio sequence。It includes Samp

5、ling, quantization, coding模 拟 音频 信 号音 频 信 号 数 字 化采 样量 化编 码按 不 同 应 用 目 标进 行 数 字 压 缩 音频信息处理框图 Transform analog audio signal into a digital meter . 1、What is the samplinglIn the process of continuous signal discrete time general, sampling is generally carried out according to the uniform time interval。

6、数字激光唱盘CD10 205020034007 k 15 k 20 k 频率 / HzFM无线电广播AM无线电广播电 话This is a schematic of common audio application bandwidth2、What is the quantitativelQuantization is each sampled values are discretized in amplitude。3、What is the codelThe encoding process is indicated by binary numbers to quantify each sam

7、pling value。 3 Audio signal compression codingl3.1 Audio signal coding classification 1、Waveform coding：Digital processing of speech signals based on waveform of speech signal processing, waveform tried to rebuild after consistent with the original signal waveform。 Advantages: simple realization, go

8、od speech quality, adaptability。 Disadvantages: compression degree is not high, need higher coding rate。 Waveform coding techniques Commonly used：DM、DPCM、ADPCM、SBC、VQ。 2、Parametric coding 3、Hybrid coding Process simultaneously use two or more than two kinds of coding method to encode。 The mixed codi

9、ng encoders include MPE-LPC、RPE-LPC、celp Etc.。3.2 Compression coding methods commonly usedl1 The general delta modulation（DM）l2 Adaptive delta modulation（ADM）l3 Differential pulse code modulationl4 The subband codingl5 Vector quantization coding 4 Audio signal compression standardl4.1 Waveform codin

10、g standard 1、standard of G.711 2、standard of G.721 3、standard of G.722 4.2 Mixed coding standard 1、standard of G.728 2、standard of G.729 3、standard of G.723.1 5 Multimedia audio signal file format The audio file is usually divided into two categories: sound files and MIDI files。 The sound file: orig

11、inal sound by sound recording equipment, recording, record of binary real sound sampling data, usually a larger file size。 MIDI file: a music instruction sequence, equivalent to the music, the electronic musical instrument can use the sound output device or connected with the computer to play, a smaller file。（1）The Wave file，Extension is wav。 （2）Audio file，Extension is AU Compressed digital audio format by Sun company, the common sound file format in Internet。（3）MPEG