MDIA 308 Digital technologies

Converting analog to digital ADC – analog to digital conversion An analog voltage is converted in binary code Binary = “two states” Expressed as “1/0” or “on/off” Each digit is called a bit Bits are combined into longer binary numbers or “bit words”

Converting analog to digital If a single digit were used to express the voltage values – there would be only two values By creating clusters of binary digits in longer strings, many values may be represented Two digits could describe four values: 00 – 11 – 10 – 01

Converting analog to digital The number of digits in the binary number or “bit word” is called the bit rate For many years the standard for consumer audio (compact disks) has been 16-bit, or binary numbers with sixteen digits 16-bit sampling will allow over 65,000 various combinations of digits 16-bit sampling produces acceptable fidelity for most puposes

Converting analog to digital Another variable which determines the accuracy of analog to digital conversion is the sampling rate Sampling rate describes how frequently the analog voltage is measured and converted into digital data

Nyquist Principle The Nyquist principle states that the highest frequency that can be sample is one half the sampling rate Thus, a sampling rate of 44,100 samples per second would accurately reproduce frequencies up to 22,050 Hz. Since most humans hear frequencies no higher than 20,000 Hz, 44.1 is acceptable

Sampling rate Each red point along the timeline represents one sample

Sampling rate A low sampling rate induces sampling error represented here as a misshapen wave form

Sampling rate A higher sampling rate reduces sampling error represented here as a more accurate wave form

Digitization At best, the digital data set is an approximation of the analog voltage that was sampled Converting the digital data back into an analog signal will have some inherent error

Digitization Over sampling and higher sampling rates produce more accurate wave forms

Data management High fidelity audio (wide frequency response and high dynamic range) requires large data sets HD video storage requires even larger data sets

Data management Down sampling or down conversion lower the sampling and bit rates to produce smaller files To help manage data, compression schemes remove redundancies and use “masking” of some content