by jj2739


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Analog
Continous signal that mimics shape of acoustic sound pressure wave
Digital
Stream of discrete numbers that represent instantaneous amplitudes of analog signal, measure at equally spaced points in time

A series of "snapshots"
Sampling Rate
How often analog signal is measured

Eg. 44,100Hz
Sampling Resolution
Precision of numbers used for measurement: the more bits, the higher the resolution.

Eg. 16 bit
Nyquist Theorem
Sampling rate must be at least twice as high as the highest frequency you want to represent
Aliasing
Occurs when sampling rate is not high enough. Also known as Foldover.

An ADC has a low-pass anti-aliasing filter to prevent this
Quanitzation Noise
Round-off error: difference between actual signal and quantization to integer values.
3-bit Quanitization
23= 8 values
4-bit Quanitization
24= 16 values
Codec
Coder-Decoder

Analog to Digital conversion device

Eg. Modem
Noise
Data that is not being used to transmit a signal, but is simply produced as an unwanted by-product of other activities.

External noise: originates in the communication medium. 
Man-made noise
Atmospheric noise(static)
Space noise(mostly solar noise)

Internal noise: originates in the communication equipment
Thermal noise(white noise)
Shot noise
Excess noise(flicker noise or pink noise)
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