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原帖由 jjx01 于 2007-12-26 17:59 发表 ![]()
( E2 I: z( M8 I' Z" a% g F》大家看上面这张图,2倍的采样率完好的重现了源信号) v/ s) A8 E2 V
( Q1 T3 h8 x. d, S: u; m正弦线最后变成了三角形组合……
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44。1也不是刚好是20的两倍……
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Why 44100? Why not make it a round decimal value like 44000, or a round binary quantity like 44032? Why not 32KHz or 48KHz? In general, the human ear can hear tones out to about 20KHz. According to a smart fellow named Nyquist, you have to sample at twice that rate. Because of imperfections in filtering, you actually want to be a little above 40KHz. According to John Watkinson's _The Art of Digital Audio_, 2nd edition, page 104, the choice of frequency is an artifact of the equipment used during early digital audio research. Storing digital audio on a hard drive was impractical, because the capacity needed for significant amounts of 1 Mbps audio was expensive. Instead, they used video recorders, storing samples as black and white levels. If you take the number of 16-bit stereo samples you can get on a line, and multiply it by the number of recorded lines in a field and the number of fields per second, you get the sampling rate. It turned out that both NTSC and PAL formats (the video standards used in US/Japan and Europe, respectively) could handle a rate of 44100 samples per second. This rate was carried over into the definition of the compact disc.
* [/ g1 R9 }( S) x" ^! ^另外,虽然不是正好的两倍,但采样出来也是和零差不多了。 |
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