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Transcript of MDIA 308 Digital technologies. Converting analog to digital ADC – analog to digital conversion An...
MDIA 308MDIA 308
Digital technologiesDigital 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