電話的缺陷
Effective speech transmission systems must be able to cope with signals having this bandwidth(5 kHz). It is interesting that one system that does not support this 5 kHz bandwidth is the telephone: Telephone systems act like a bandpass filter passing energy between about 200 Hz and 3.2 kHz. The most important consequence of this filtering is the removal of high frequency energy. In our sample utterance, the “ce” sound in “Rice” contains most of its energy above 3.2 kHz; this filtering effect is why it is extremely difficult to distinguish the sounds “s” and “f” over the telephone. Try this yourself: Call a friend and determine if they can distinguish between the words “six” and “fix”. If you say these words in isolation so that no context provides a hint about which word you are saying, your friend will not be able to tell them apart.
昨天在網上閱讀一些關於 FYP 的 Paper 時，得知原來電話是不能夠支援 5kHz 頻寬的。而人的聲音大約能夠去到 5 kHz，但是電話的頻寬只能夠去到 3.2 kHz 的頻寬，所以當說一些高過 3.2 kHz 頻寬的字時就聽不清楚了。昨晚，我也作過這樣的實驗，在電話中分別說出 six 和 fix 兩個字讓對方分辨一下，結果是他們真的分辨不出來，這可算是電話的缺陷吧﹗