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Designing Web Audio & CD-ROM by Dylan Thede, Josh Beggs

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Digital audio demystified

Sound is converted to digital information by means of a circuit that creates a set of numbers corresponding to the shape of an incoming electrical wave or current. Two sets of binary values represent digitized waveforms: sampling rate and bit-depth. A sample is the value and position assigned to a point of an electrical waveform. The number of samples taken per second is called the sampling rate. Bit-depth refers to the size of the binary numbers assigned to describe the dynamic value of each sample.

Sampling is the most important part of the digitizing process. A sample is simply a snapshot of a sound at a given point in time. The sampling rate is a measurement of how many snapshots are taken. To understand this, think about film. A movie camera takes 24 still photographs per second. When they are played back at a certain speed in the theater, the result is almost indistinguishable from reality. Each frame of film is a sample; 24 frames per second is the sampling rate. If you were to film at a lower sampling rate, there would be less information for each second of film. The result would be jerky motion. If you filmed at an even slower rate, the illusion of motion would disappear completely; the film would look like a sequence of still images (which it is).

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