Transcript Fundamentals of Audio Production

Fundamentals of Audio
Production
Chapter Three:
Digital Audio
Fundamentals of Audio
Production. Chapter 3
1
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”
Fundamentals of Audio
Production. Chapter 3
2
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
Fundamentals of Audio
Production. Chapter 3
3
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
Fundamentals of Audio
Production. Chapter 3
4
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
Fundamentals of Audio
Production. Chapter 3
5
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
Fundamentals of Audio
Production. Chapter 3
6
Sampling rate
Each red point along the timeline represents one sample
Fundamentals of Audio
Production. Chapter 3
7
Sampling rate
A low sampling rate induces sampling error
represented here as a misshapen wave form
Fundamentals of Audio
Production. Chapter 3
8
Sampling rate
A higher sampling rate reduces sampling error
represented here as a more accurate wave form
Fundamentals of Audio
Production. Chapter 3
9
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
Fundamentals of Audio
Production. Chapter 3
10
Digitization
Over sampling and higher sampling rates produce more accurate wave forms
Fundamentals of Audio
Production. Chapter 3
11
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
Fundamentals of Audio
Production. Chapter 3
12
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
Fundamentals of Audio
Production. Chapter 3
13
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
Fundamentals of Audio
Production. Chapter 3
14