Fundamentals of Audio Production. Chapter 3

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Fundamentals of Audio Fundamentals of Audio ProductionProduction

Chapter Three:Chapter Three:

Digital AudioDigital Audio

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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”

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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

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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

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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

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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

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Sampling rate

Each red point along the timeline represents one sample

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Sampling rate

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

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Sampling rate

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

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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

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Digitization

Over sampling and higher sampling rates produce more accurate wave forms

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Data management

• High fidelity audio (wide frequency response and high dynamic range) requires large data sets

• To accommodate high fidelity audio, high capacity storage systems are necessary

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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

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Data management

• 44.1 Khz .WAV file

• 22.1 KHz .WAV file

• 11.8 KHz .WAV file

• 8.8 KHz .WAV file

• 16 KHz .AU file

• 22.1 KHZ .MP3 file