专业外语-多媒体-音频信号

1、Lecture 15: Introduction to multimedia: audio2013.5Outline Background Text tour Vocabulary Difficult points Text tour 英译汉 汉译英背景介绍(Background) 在计算机系统中，组合两种或两种以上媒体的一种人机交互式信息交流和传播媒体。使用的媒体包括文字、图片、声音 (包含音乐、语音旁白、特殊音效)、动画和影片，以及程式所提供的互动功能。 本讲中重点讲解多媒体中的音频与图像方面的知识 音频部分包括音频传输、音频压缩、音频格式等内容。 图像部分包括图像基本知识、图像压缩、图像

2、格式等。语音频率与采样 人耳听到的语音频率范围为20Hz-20kHz。其中，人耳对1kHz-4kHz范围的语音频率最为敏感。 根据尼奎斯特采样定理，要获得不失真的语音信号，采样频率需在40kHz以上。例如，高保真音频采用44.1kHz采样频率。 为了传输需要，很多系统(如电话系统)采用8kHz采样频率，保留语音中对人类最敏感的频率部分。 语音合成技术（如线性预测编码:LPC）可以更大限度的压缩语音信号。音频制式：MP3 MPEG: Moving Picture Experts Group (动态图像专家组)。MPEG标准主要有以下五个，MPEG-1、MPEG-2、MPEG-4、MPEG-7及M

3、PEG-21等。该专家组建于1988年，专门负责为CD建立视频和音频标准 MP3：MPEG-1 audio layer 3Paragraph 1Multimedia is media and content that uses a combination of different content forms. Multimedia includes a combination of text, audio, still images, animation, video, or interactivity content forms. Multimedia is usually recorded

4、 and played, displayed, or accessed by information content processing devices, such as computerized and electronic devices, but can also be part of a live performance. Multimedia devices are electronic media devices used to store and experience multimedia content. Multimedia is distinguished from mi

5、xed media in fine art; by including audio, for example, it has a broader scope. The term “rich media” is synonymous for interactive multimedia. Hypermedia can be considered one particular multimedia application. From WikipediaVocabulary Multimedia: 多媒体 Content forms: 内容格式 Animation: 动画 Interactivity

6、：相互，交互 Store：存储 Mixed media：复合媒体，综合材料 Device: 器件，设备Vocabulary Still image: 静态图像 Video：视频 Audio: 音频 Text：文字 Hypermedia： 超媒体 Synonymous： 代名词 Rich media: 富媒体，互动式媒体 Live performance: 现场表演Difficult pointMultimedia includes a combination of text, audio, still images, animation, video, or interactivity con

7、tent forms. a combination of: 组合 翻译：多媒体是由文字、音频、静态图像、动画、视频及交互程序组合而成的。Difficult point Multimedia is usually recorded and played, displayed, or accessed by information content processing devices, such as computerized and electronic devices access: 存取，访问。 例如：程序设计中，指针的非法访问会报错access violation。 翻译：多媒体一般是利用

8、信息处理设备如电子与计算机设备来对媒体内容进行记录和播放、显示与存取。Difficult point Multimedia is distinguished from mixed media in fine art; distinguish from: 与。区别翻译：多媒体与美术中的复合媒体是不一样的。Paragraph 2 CD-quality audio requires a transmission bandwidth of 1.411 Mbps. Clearly, substantial compression is needed to make transmission over t

9、he Internet practical. For this reason, various audio compression algorithms have been developed. Probably the most popular one is MPEG audio, which has three layers (variants), of which MP3 (MPEG audio layer 3) is the most powerful and best known. Large amounts of music in MP3 format are available

10、on the Internet, not all of it legal, which has resulted in numerous lawsuits from the artists and copyright owners. MP3 belongs to the audio portion of the MPEG video compression standard. Vocabulary CD-quality: CD音质 Transmission bandwidth: 传输带宽 Compression: 压缩 substantial compression：高度压缩 MPEG：Mov

11、ing Pictures Experts Group，多媒体一种常用格式 MP3：MPEG-1 Audio Layer 3Vocabulary Algorithms： 算法 Legal: 合法的 Lawsuit：诉讼 Portion: 组成部分 Numerous：大量的 Available: 可用的 Copyright：版权 Standard：标准Difficult point CD-quality audio requires a transmission bandwidth of 1.411 Mbps. CD-quality audio: 高音质音频 翻译：传送高音质音频需要1.411兆带

12、宽。 Difficult point Large amounts of music in MP3 format are available on the Internet, not all of it legal, which has resulted in numerous lawsuits from the artists and copyright owners. result in: 导致，由此而来 翻译：互联网上有大量的MP3格式的音乐资源。但是，由于版权问题，它们有些是非法的。艺术创作者与版权所有者提起的大量诉讼案件也由此而来。Paragraph 3 Table 1 shows t

13、he tradeoff between sound quality and data rate for these three categories. High fidelity music system sample fast enough (44.1 kHz), and with enough precision (16 bits), that they can capture virtually all of the sounds that humans are capable of hearing. This magnificent sound quality comes at the

14、 price of a high data rate, 44.1kHz16bits= 706kbits/sec. This is pure brute force. Vocabulary Tradeoff: 平衡的，折中的 High fidelity music:高保真音乐 Precision: 精度 Virtually： 简直，实质上 Magnificent: 华丽的，优秀的 Capture：采集，捕捉 Difficult point Table 1 shows the tradeoff between sound quality and data rate for these three

15、categories. Tradeoff between: 兼顾，折中考虑，平衡 翻译：表1显示这三种音频制式对音质与数据码率这两个指标上折中考虑。Difficult point This magnificent sound quality comes at the price of a high data rate, 44.1kHz16bits= 706kbits/sec. at the price of: 付出.的代价 翻译：高音质带来的代价就是高达706kbits/sec的数据码率。英译汉 The range of human hearing is generally considere

16、d to be 20 Hz to 20 kHz, but it is far more sensitive to sounds between 1 kHz and 4 kHz. For example, listeners can detect sounds as low as 0 dB SPL at 3 kHz, but require 40 dB SPL at 100 hertz (an amplitude increase of 100). Listeners can tell that two tones are different if their frequencies diffe

17、r by more than about 0.3% at 3 kHz. This increases to 3% at 100 hertz. For comparison, adjacent keys on a piano differ by about 6% in frequency. 英译汉 Audio processing covers many diverse fields, all involved in presenting sound to human listeners. Three areas are prominent: (1) high fidelity music reproduction, such as in audio compact discs, (2) voice telecommunications, another name for telephone networks, and (3) synthetic speech, where computers generate and recognize human voice patterns. While these applications have different goals and problems, they are link