fundamentals of audio production
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Fundamentals of Audio Production. Chapter Three: Digital Audio. 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 - PowerPoint PPT PresentationTRANSCRIPT
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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