雙語暢銷書《艾倫圖靈傳》第6章:連接兩個世界(7)
Alan had probably already learnt about the Vocoder when in Britain, since Dollis Hill had received information on it in 1941.
It was a very advanced piece of communications technology, which had been patented by the Bell engineer H. W. Dudley in 1935 and developed since then at the Bell laboratories.
這是一項非常先進的通信技術，1935年貝爾工程師H.W.達德雷註冊了該專利，從此以後它就在貝爾實驗室不斷得到改進。The idea of the Vocoder was to abstract the essential elements of speech, throwing away much of its redundancy, and conversely to reconstruct the speech signal from its essential components.
聲碼器的概念是，將聲音的基本元素抽出來，去掉多餘的元素，然後再用這些基本元素來重建語音信號。
One way of thinking of this process was to regard it as reducing the bandwidth, or frequency range, of a speech signal.
這個過程是爲了降低語音信號帶寬，或者說頻率範圍。Any Bell Labs engineer would be familiar with the idea of reducing the frequency range of speech, since the telephone cut off sound above 4000 Hz.
貝爾實驗室的任何一個工程師，對降低聲音的頻率範圍都很熟悉，因爲電話會削去4000Hz以上的聲音。The resulting lack-lustre tones were still perfectly comprehensible, the point being that higher frequencies were redundant in ordinary applications.
這使電話的聲音總是死氣沉沉，但完全可以聽懂，也就是說，普通應用中並不需要更高的頻率。But to reduce that frequency limit much further would produce a sort of miserable grunting, which would not do at all.
但是，如果進一步直接削減頻率，就會產生一種嚴重的嘟噥聲，這就無法使用了。The Vocoder did something far more sophisticated. It collected information about the amplitude of the speech signal at each of ten frequencies up to 3000 Hz,
聲碼器通過一種更精密的方式來削減頻率，它在3000Hz以下的10個頻率點上，and also took an eleventh component which coded either the fundamental pitch of the sound or (during unvoiced sounds like ssss) an absence of pitch.
採集一個對應該頻率的振幅信息，然後對其進行編碼。Each of these eleven signals required a frequency range of only 25 Hz.
這樣編碼出來的每個信號，頻率範圍只有25Hz。In this way, sufficient information was abstracted for intelligible speech to be reconstructed, and yet the total bandwidth was confined to less than 300 Hz.
這樣的方法，就能將語音信息需要的總帶寬限制在300Hz以內，而且能保證足以能夠聽懂的語音質量。
