Flashcards in Pot Purri Deck (98):
Sound Design for Visual Media program concentrates on two main career fields:
sound for film and television, and game audio (sound for video games).
stereo technique uses
2 or more mics
what mic is good for room ambience?
omni-directional mic records from where?
all 360 angles
type of unidirectional mic
what is sound?
a series of pressure waves produced by vibration
Sound waves travel through the air and cause your eardrum to
oscillate (move back and
forth) in response to the sound
Like ocean waves breaking on a beach, sound waves alternately press forward and recede back
Parts of sound wave
Amplitude (up/down) wavelength (across)
Amplitude of sound wave determined by
Increased and Decreased atmospheric pressure
height of the wave (or amplitude) corresponds to
The loudness or volume of a sound results from the
amount of pressure produced by the sound wave
Sound pressure level
Volume is measured in
The softest audible sounds occur at the
threshold of hearing
The volume of normal conversation is about _____ above threshold
The threshold of
pain is at about
With audio in a
recording system, if we increase a sound’s level by ___dB,
6 dB, it will sound about twice as loud
Difference in volume between loudest and quietest sound
The human ear has a dynamic range of _____ between the ___________
130 dB between the thresholds of hearing
Tape noise, or hiss, is always present in analog recordings and, like the shuffling
sounds of the symphony audience, it determines the lower limit of the dynamic range (the noise floor).
signal-to-noise (s/n) ratio
dynamic range of a tape recorder
What is perceived as pitch is determined by the ________
frequency of the sound wave
Frequency is a measure of
Frequency is a measure of how frequently the waves of sound pressure strike the ear—that is, how many cycles of pressure increase/decrease occur in a given length of time.
Frequency was formerly measured in cycles per second; now the same unit is called a hertz (Hz)
Musical notes are standardized
according to their frequency. Orchestras usually tune up to concert A, which is 440 Hz.
Doubling any frequency produces
a tone one octave
The ear can sense low frequencies down to about
sounds above 20,000 Hz are audible to dogs and bats, but seldom humans.
When sound volume is low, the ear is much more sensitive to ______ than ________
midrange frequencies (2,000 to 4,000 Hz) than to low or high frequencies.
e. Some audio equipment has a “loudness”
control that increases the low bass when the volume is down to compensate for this deficiency
A violin string vibrates at a basic frequency (called the
fundamental), as well as at various multiples of this frequency. These other frequencies are called harmonics or overtones, and they are usually
quieter than the fundamental.
The relative strengths
of the harmonics determine
tone quality or timbre.
Sounds like speaking or door slam have what type of pitch and harmonic distribution?
sounds, such as a speaking voice or a door slam, have no discernible pitch; their harmonics are more complexly distributed.
how an audio system responds to various frequencies of sound
ex of frequency response
at low volume the ear
favors middle-frequency sounds, and at high volume its frequency response is more even or flat.
a good audio recorder's frequency response
A good audio recorder is capable of providing a
fairly flat frequency response throughout the frequency range of human hearing.
if you change the frequency response of your equipment by increasing or decreasing
the response to low, middle, or high frequencies, you can change
the character of the sounds.
Equalizers are often used to
alter the frequencies of sounds during recording or after.
With an equalizer you could _______
you could boost low frequencies to make, say, a truck engine sound deep, rumbly, or menacing, or you could boost the high
frequencies of a piano to make its sound “brighter.”
If we diminish high frequencies without changing the bass, the effect is
like putting cotton in your
ears: The sound is muddy and dull.
"Telephone Sound" frequency
Telephones have a fairly limited frequency response, which is centered on the middle frequencies needed to understand speech. In movies, the
sound of someone talking through a phone can be simulated with an equalizer by cutting the low and high frequencies and boosting the midrange.
How does a microphone work?
The microphone responds to sound waves by producing electrical waves that have essentially the same character in terms of frequency and
Most modern microphones employ an extremely light diaphragm that can move with the slightest variations in sound pressure.
moving-coil microphones have a
very light coil of wire attached to the diaphragm
When the diaphragm moves back and forth, the
coil moves past a magnet and creates an alternating electric current that flows through the wires in the coil. Thus, sound pressure is translated into
electric pressure, or voltage.
Voltage from mic and the pre-amp & then
This voltage travels from the microphone to a mic preamp (preamplifier), which increases its strength, and may supply the mic with power & then it goes to the magnetic "recording head"
A recording head is an
electromagnet, not unlike the ones used in metal scrap yards or that kids
sometimes play with.
When electricity passes through the head it
generates a magnetic field.
The head is a
C-shaped piece of metal with wire coiled around it.
On the front of the head is an extremely narrow opening called the gap. The head completes a flow of energy: Advancing and receding sound
waves become electrical waves, which finally result in a magnetic field that is oriented first in one direction and then in the opposite.
Components of magnetic tape
Magnetic tape is made up of a thick support material or base and a thin emulsion that stores the information
Tape emulsion is called oxide and
contains small particles of iron.
The components of the iron in oxide
Each piece of iron is a miniature bar magnet with distinct north and south poles
When a particle of iron passes the
gap in the recording head, the magnetic polarity of the particle aligns itself with the magnetic field at the head. When the tape moves on, it
maintains that alignment. Since the magnetic field is always alternating back and forth, any given stretch of tape contains groups of particles that
alternate in their alignment. The orientation of the particles corresponds to the original sound in this simplified way:
The louder the sound, the more
particles will be forced to line up the same way; the higher the frequency, the closer together the alternating groups will be.
When you play back the tape, it is passed over the same head, or a similar playback head. Now the magnetic field stored in the iron particles
creates an electric current in the wires coiled around the head. This signal is amplified and sent to a loudspeaker, which acts like a moving-coil
microphone in reverse
Instead of the microphone’s diaphragm, the speaker employs a paper cone that is connected to the coil. When current
passes through the coil, it moves the cone, which in turn pushes the air to produce sound pressure waves. If you stand in front of a large bass
speaker, you can both hear and feel the sound waves generated by the paper moving back and forth.
could the same microphone
feed an analog or digital recorder)?
With analog recording, sound is converted to a ______ then _________
voltage; the voltage is converted to a magnetic field, which is then stored on tape.
In digital audio
recording, we start the same way: Sound is converted to ____ then ________
a voltage. Then the analog-to-digital (A/D) converter
The level of the signal at each sample is measured
according to a level scale (the horizontal lines). The total number of units in the scale is determined by the number of bits in the system; a three-bit
system is pictured here
Samples can only be measured in
How can we make a higher resolution recording in regards to sample rate?
By taking more samples in the same period of time (higher sample rate) and using more bits
per sample, we can make a higher-resolution recording.
Pictured here is a four-bit system with twice the sampling rate as the middle graph. Now
the scale has finer gradations, allowing us to measure the signal more precisely. Note that this curve better approximates the shape of the original
Picture of more pinpoints on a graph
two-step process is the heart of digital recording:
processes the sound by repeatedly measuring the voltage level (sampling it) and converting those measurements to numbers (quantizing).
(sample rate and frequency) To accurately measure the level of high-frequency sounds we need to
take samples more
frequently than for low sounds.
A Swede named ________ proved that ____________
Henry Nyquist proved that the sampling rate has to be at least twice the maximum frequency we hope to capture
. Because humans can perceive
sounds up to about ___________, a digital audio recorder needs to sample at least ______ times a second to capture that range of frequencies
20,000 Hz (20 kHz), 40,000 (40 kHz)
Too low a sample rate results in _________
aliasing, with poor high-frequency reproduction.
The higher the sample rate, the
better the frequency response and quality
Many video cameras and
recorders use sample rate of
Very high-quality recorders used for high-end production and music recording
may operate at 96 kHz or even 192 kHz
Some DV cameras can be operated at 32 kHz—a low sample rate that compromises quality.
Sample rate is an expression of
how often we measure the audio signal
Bit depth or _______ refers to _________
precision, how accurately we measure each
Poor Bit depth stick analogy
Say you had to measure people’s height with a stick. The stick is one foot long and
you can only recordthe height in one-stick increments. So, you could measure a six-foot-tall man very accurately (six sticks). But when you measure
a woman who’s five feet, six inches tall, you either have to record her height as five sticks or six sticks—either way, you’re off by half a foot.
Good Bit depth stick analogy
Now, imagine that we do the same thing with a shorter stick that’s only six inches long. We can still measure the man’s height precisely (twelve
sticks). And when we measure the woman, now we can be just as accurate (eleven sticks).
Digital systems use a _________ to ________.
The scale has ________
a measurement scale to record the voltage of each audio sample. The scale has a number of levels.
In an 8-bit system there
are ___ levels
Levels in bit depths are like our
measuring sticks from analogy
Quantizing error is a form of
If the signal level fell midway between 125 and 126, it would be rounded down to 125 or up to 126, introducing
an error that could degrade the sound
For greater precision we could use more
In a 16-bit system (which is fairly typical in professional video cameras) there are _________
More levels allow one to
measure different voltage levels much more accurately and reproduce sounds more precisely
The more bits used for each sample,
higher the quality and the lower the noise.
However, increasing bit depth, like raising the sample rate,
increases the amount of audio data to be
processed and stored.
Some high-quality recording systems use how many bits?
20 bits or 24 bits or more
Even though you might not be able to hear the difference between 16 bits
and 24 bits, when digital audio gets processed during postproduction, errors get multiplied, so more precision keeps the sound cleaner in the
The noise floor
Sounds that are lower than the first level will disappear entirely
from the recording (they will be recorded as zero)
But if we use more bits, the first level is now lower, and we may be able to
catch quiet sounds that would have been too low to register before. This reduces _______ increases _______
reduces noise and increases dynamic range.8
together ______ and ______ contribute to the resolution of a digital audio recording
sample rate and bit depth
Low-resolution recordings may sound
overly crisp (“cold”).
recordings sound more
faithful to the original sound source in terms of frequency response, dynamic range, and lack of noise
With digital audio or video, it’s very easy to move data
you only need ones and zeros to represent any value.