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When CDs come out in the early 1980s, their single purpose in life was to hold music. So to understand how a CD works, we need to understand how digital recording and playback work.
Thomas Edison created the first device for recording and playing back sounds in 1877. He used a very simple mechanism to store an analogue wave. In Edison's original phonograph a diaphragm controlled a needle and the needle scratched an analogue signal onto a thin foil cylinder. During playback, the vibrations pressed into the tin cause the needle to vibrate, causing the diaphragm to vibrate and play the sound. Modern phonographs work in the same way, but the signals read by the needle are amplified electronically. The problem with the simple approach is that the fidelity is not very good and if a phonograph is plaid repeatedly, eventually it will wear out.
In a CD the goal is to create a recording with very high fidelity and perfect reproduction. To accomplish these two goals, digital recording converts the analogue wave into a stream of numbers and records the numbers instead of the wave. The conversion is done by a device called an analogue-to-digital converter. Then to play back the music, the stream of numbers is converted back to an analogue wave by a digital-to-analogue converter (DAC). The analogue wave produced by the DAC is amplified and fed to the speakers to produce the sound.
When you sample the wave with an analogue-to-digital converter there are 2 variables. They must be controlled. The first is the sampling rate. The rate controls how many samples are taken per second. The second is the sampling precision. The precision controls how many different gradations are possible when taking the sample.
In the case of CD sound the sampling rate is 44,100 samples per second and the number of gradations is 65,536. At this level the output of the DAC so closely matches the original wave form that the sound is essentially "perfect" to most human ears.
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