Appendix B: An Introduction to Digital Recording
Converting Sound into Numbers
In a digital recording system, sound is represented as a series of numbers,
with each number representing the voltage, or amplitude, of a sound wave at
a particular moment in time. The numbers are generated by an
analog-to-
digital converter
, or ADC, which converts the signal from an analog audio
source (such as a guitar or a microphone) connected to its input into
numbers. The ADC reads the input signal several thousand times a second,
and outputs a number based on the input that is read. This number is called a
sample.
The number of samples taken per second is called the
sample rate
.
On playback, the process happens in reverse: The series of numbers is
played back through a
digital-to-analog converter
, or DAC, which converts
the numbers back into an analog signal. This signal can then be sent to an
amplifier and speakers for listening.
In computers,
binary numbers
are used to store the values that make up the
samples. Only two characters, 1 and 0, are used. The value of a character
depends on its place in the number, just as in the familiar decimal system.
Here are a few binary/decimal equivalents:
BINARY
DECIMAL
0000000000000000
0
0000000000000001
1
0000000000000011
3
0000000000000111
7
0000000000001111
15
0000000000011111
31
1111111111111111
65,535
Figure A. Binary numbers and their decimal equivalents
Each digit in the number is called a
bit.
The binary numbers expressed in
figure A are sixteen bits long, and have a maximum value of 65,535. The
more bits that are used to store the sampled value, the more closely it will
represent the source signal. In a 16-bit system, there are 65,535 possible
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