Literally, multimedia means TWO or more media. If the publisher of this book Wanted to join the Current hype about multimedia, he could advertise the book as using multimedia technology. After all, it contains two media：text and graphics(the figures). Nevertheless, when most pepole refer to multimedia, they generally mean the combination of two or more continuous media, that is, media have to be played during some well-defined timed times interval, usually With the users interaction. In practice, the two media are normally audio and video, that is, sound plus moving pictures.

    In the multimedia environment, we have graphics and text at the same time, we can also add the photograph, animation, good-quality sound, and full motion video. All of the technologies make computers more interesting and much easier to use. For example, a multimedia program can play a segment of movie：a cat was playing a reel of thread, with "mewing…" The tableau can a be immediately captured and pasted to a text at the side of a paragraph of words.

    CD－ROM

    CD－ROM is an optical technology that is used to make compact disks for CD stereo systems；it has now been adapted to store data for computers. CD disk is an optical disc, on which data is recorded as a set of dips in the surface. When a laser beam shines across the dips, the reflected distortion represents the data. Optical disc has a 600 megabyte capacity and are well suited for the computer applications needing the vast storage. The playback effect of optical discs for music is very perfect, no hiss and crackle as with other photo-records. A computer system must have a CD drive that is designed to read the disks and translate the data into a form it can process. CD disks can store huge volumes of data and are very useful for reference material an encyclopedia, for example. However, as the name(read-only memory)implies, CD disks cannot be written on or changed in any way.

    Musical Instrument Digital Interface

    Musical Instrument Digital Interface, or MIDI, is a communication interface provided on virtually every synthesizer made today. It provides a standard that allows Products by different companies to communicate with each other. MIDI's original purpose as to allow a musician to control several synthesizers from one keyboard rather than connecting a number of keyboard-equipped synthesizers, to produce the multilayered sound. The MIDI standard provides for 16 channels. You can assign each channel to a specific synthesizer or synthesizer voice. If you record a sequence and assign it to channel 5, for example, only an instrument set to listen on channel 5 plays back the sequence, this feature enables MIDI networks to sound like orchestras.

    Audio

    An audio(sound) wave is a one-dimensional acoustic(pressure) wave. When an acoustic wave enters the ear, the eardrum vibrates, causing the tiny bones of the inner ear to vibrate along with it, and sending nerve pulses to the brain. These pluses are perceived as sound by the listener. Audio waves can be converted to digital form by an ADC (Analog Digital Converter). An ADC takes an electrical voltage as input and generates a binary number as output. Music, of course, is just a special case of general audio, but an important one. The representation, processing, storage, and transmission of such audio signals are a major part of the study of multimedia systems.

    Virtual Reality－Enter a Fancy Space

    In the science fiction "Neuromancer", William Gibson describes a space, Cyberspace, controlled by a computer. Once his brain was linked with the computer, a man would undergo all experiences in the space. His various senses in the realistic world would be replaced with a series of new electric stimuli. The Cyberspace is regarded as a goal of future virtual reality. 

    In fact, virtual reality is exploiting software and hardware of the computer to generate a simulation of an environment, such as an easeful classroom, a breathtaking action and so on. In such a simulated environment, one would have an immersed sense. For example, in a Virtual space, Students can "dissect" a human body, "visit" ancient battlefields, or "talk" with Shakespeare, …

    從字面上看，多媒體是指兩種或兩種以上媒體。如果本書的出版者想加入當前多媒體廣告的行列，那么，他就可以聲稱這本書已經使用了多媒體技術。因為，畢竟，它包含兩種媒體，文本和圖形（插圖）。然而，當大多數人談及多媒體時，他們通常是指混合了兩種或兩種以上連續(xù)的媒體，即，媒體可以在一段規(guī)定的時間之內連續(xù)播放，并且通常伴隨著與用戶的交互。實際上，這兩種媒體通常指音頻和視頻，即聲音加移動的圖片。

    在多媒體環(huán)境中，我們可以同時擁有圖形和文本，也可以增加圖片、動畫、高質量的音響和全動錄像，這些技術使得計算機使用起來更有趣也更容易。例如，一個多媒體程序可以播放一段電影：一只小貓正在玩線團，發(fā)出“喵喵”的聲音……，這個畫面可以立即剪貼到一段文字旁邊。

    CD-ROM

    CD－ROM原是一種用于制作CD立體聲系統(tǒng)的小型圓盤的光學技術，現(xiàn)在它已經被用來為計算機儲藏數據。CD盤是一種光盤，其數據以一組坑的形式記錄在光盤表面上，當激光束掃過這些坑的時候，返回的失真程度就代表了這些數據。光盤有600兆字節(jié)的容量，非常適合需要大存儲量的計算機應用。音樂光盤播放音樂的效果非常完美，沒有像用其他唱片那樣的嘶嘶聲和噼啪聲。計算機系統(tǒng)必須配備一個CD驅動器用來讀取光盤并將數據轉換到計算機能夠處理的形式。CD盤可以儲存大量數據，這對于文獻資料的存儲非常有用，如存儲一部百科全書。然而，正如其名字（只讀存儲器）所指出的那樣，CD盤不能寫，也不能用任何方式改變其內容。

    音樂設備數字接口

    音樂設備數字接口，或稱MIDI，實際上是為目前制造的各種合成器提供的一種通信接口。它提供的標準允許不同廠家生產的音樂產品可以進行通信。MIDI原本的目的并不是為了連接許多裝備了鍵盤的合成器來產生多層次的聲音,而是為了使音樂家能夠用一個鍵盤控制幾個合成器進行演奏。MIDI標準提供16個聲道，你可以為每一個聲道設置一個特別的合成器或合成器聲音。例如，你記錄了一個音樂序列并將它設置到第五聲道上，并且只有一種樂器在第五聲道上回放這個音序，其效果使MIDI網聽起來很像樂隊。

    聲波

    聲波是一維的聲學（氣壓）波，當聲波進入人的耳朵時，耳膜振動，引起耳朵內部的一些小骨頭振動，并向大腦發(fā)出神經脈沖，這些脈沖被聽者作為聲音聽到了。聲波可以通過ADC（模擬數字轉換器）轉換到數字形式，ADC采用電壓作為輸入并產生二進制數作為輸出。當然，音樂是聲波的一種特殊情況，但卻是重要的一種。這些音頻信號的表達、處理、存儲和轉換是多媒體系統(tǒng)研究的主要部分。

    虛擬現(xiàn)實——進入想像的空間

    William Gibson在他的科幻小說《Neuromancer》中描述了一個計算機控制空間Cyberspace，一個人只要將自己的大腦與計算機連接起來，進入Cyberspace，就可以體驗在該空間的一切遭遇。一套全新的電子刺激將代替人在真實世界的各種感覺。這個Cyberspace被認為是未來虛擬現(xiàn)實的目標。

    實際上，虛擬現(xiàn)實就是利用計算機的軟件和硬件去產生一種境界的仿真，如仿真一個學習場所，一次驚險的行為等等，人在這個仿真的環(huán)境中，有一種“身臨其境”的感覺。如，在虛擬的空間中，學生們可以“解剖”人體，“參觀”古戰(zhàn)場，與莎士比亞“對話”等等。