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发表于 2009-6-23 23:16:11
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至于PCM是什么。
Pulse code modulation (PCM) is a digital scheme fortransmitting analogdata. The signals in PCM are binary; that is, there areonly two possible states, represented by logic 1 (high) and logic0 (low). This is true no matter how complex the analog waveformhappens to be. Using PCM, it is possible to digitize all forms ofanalog data, including full-motion video, voices, music, telemetry, and virtual reality (VR).
To obtain PCM from an analog waveform at thesource (transmitter end) of a communications circuit, the analogsignal amplitude is sampled (measured) at regular time intervals.The sampling rate, or number of samples per second, is severaltimes the maximum frequency of the analog waveform in cycles per second or hertz. The instantaneousamplitude of the analog signal at each sampling is rounded off tothe nearest of several specific, predetermined levels. Thisprocess is called quantization. The number of levels is always apower of 2 -- for example, 8, 16, 32, or 64. These numbers can berepresented by three, four, five, or six binary digits (bits)respectively. The output of a pulse code modulator is thus aseries of binary numbers, each represented by some power of 2bits.
At the destination (receiver end) of thecommunications circuit, a pulse code demodulator converts thebinary numbers back into pulses having the same quantum levels asthose in the modulator. These pulses are further processed torestore the original analog waveform.
[ 本帖最后由 mifeng 于 2009-6-23 23:18 编辑 ] |
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第2点能听出来的话就真的太牛X了，特别是录音比较短的话
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