Pro Tools 101_ An Introduction to Pro Tools 11 ( PDFDrive )

are synonymous—15,000 CPS is the same as 15,000 Hz. Multiples of 1,000
Hz are often denoted as kilohertz (kHz). Therefore, 15,000 Hz is also written
as 15 kHz.
As the frequency of vibration increases, the pitch of the sound goes up—
numerically higher frequencies produce higher pitches, while numerically
lower frequencies produce lower pitches. Each time the frequency doubles,
the pitch raises by one octave. By way of example, the A string on a guitar
vibrates at 110 Hz in standard tuning. Playing the A note on the 12th fret
produces vibrations at 220 Hz (one octave higher).
Amplitude
The intensity or amplitude of the sound pressure variations that reaches our
ears creates our perception of the loudness of the sound. We measure
amplitude in decibels (dB). The decibel scale is defined by the dynamic
range of human hearing, with the threshold of hearing defined as 0 dB and the
threshold of sensation or pain reached at approximately 120 dB. The dB is a
logarithmic unit that is used to describe a ratio of sound pressure; as such, it
does not have a linear relation to our perception of loudness.
As the amplitude of pressure variations increases, the sound becomes louder.
Doubling the intensity of sound-pressure variations creates a gain of 3 dB;
however, we do not perceive this change as doubling the sound’s loudness.
An increase of approximately 10 dB is required to produce a perceived
doubling of loudness. By way of example, the amplitude of ordinary
conversation is around 60 dB. Increasing the amplitude to 70 dB would
essentially double the loudness; increasing amplitude to 80 dB would double
it again, quadrupling the original loudness.
Recording and Playing Back Analog Audio
The task of a recording microphone is to respond to changes in air pressure
—the waveforms, frequencies, and amplitudes that make up a sound—and
translate them into an electronic output that can be captured or recorded. The
continuous electrical signal produced by a microphone is an alternating
current with a waveform, frequency, and amplitude that directly corresponds
to, or is analogous to, the original acoustic information. Hence the term
analog audio.