Audio Production Ch 2

The Science of Sound

sound, audio, hearing

in order to produce good quality audio, we have to understand:

sound

what is the term for: changes in air pressure cause by a vibrating object

all around; in a 3d globe shape and then bounces off flat surfaces

what direction does sound travel in

when an object making sound moves forward creating a higher air pressure

what is compression

when an object making sound moves backwards creating lower air pressure

what are rarefactions

transducer; ears, guitars, microphones

what is a device that converts one form of energy into another called; give examples

waveform

what is a graphic representation of changes in amplitude over time called

soundwaves are too complex and can’t be represented with a picture or graph

what is the difference between soundwaves and waveforms

amplitude

what is the term for how low the voltage levels of the audio signal are

distance above or below the centerline of the waveform

how is amplitude represented on a waveform graph

amount of pressure in a soundwave

what is amplitude in relation to sound

how fast pressure changes repeat in a soundwave or the number of cycles per second

what is frequency

as pitch

how is frequency perceived

Hertz (Hz) or Kilo-Hertz (KHz) when over 1,000

what is frequency measured in

20Hz to 20KHz

what frequencies can people with excellent hearing perceive

2 phases

what is one complete cycle when looking at frequency on a chart

in degrees like a circle; 360 is one complete cycle and 180 is only half of a cycle

how is frequency measured on a chart

how accurately a device will pass frequencies thorough itself; a graph

what is frequency response and what is it represented by

perfectly flat (doesn’t exist)

what does a perfectly accurate frequency response look like on a chart

how fast sound travels; 1,130ft per second/68F

what is velocity and what is sound’s velocity

the physical distance of one cycle of a wave; greek letter lambda (looks like an A with no line)

what is wavelength and what is it represented by

diving velocity of sound by the frequency

how do you calculate wavelength

the longer or more complex reflected paths of sound

what are late reflections in relation to reflection of sound

how much the elements of a wave align in time with another wave

what is phase

frequency and amplitude

what are the elements of a wave

the amount of time that one wave is ahead or behind another wave

what is phase shift

phase shift

what does the space between each wave represent

phase

what does how much the lines overlap at the same time represent

when two waves share the same features at the same time

what is in phase

the sound wave that occurs when two soundwaves are in phase and combined that is the same as the two waves but twice the amplitude

what is constructive interference

when the features of two waves are the same but the cycles occur 180 degrees different in time (opposite); phase reversal

what is out of phase and what is another name for it

phase consolation that results when two out of phase waves are combined and create a decrease in amplitude

what is destructive interference

an artificially created pure tone that consists of single frequency

what is a sine wave

natural sounds are complex waves while sine waves are only one frequency

what is the difference between natural sounds and sine waves

the presence of several different frequencies within a complex sound sound wave in addition to its fundamental frequency

what is harmonic content

the lowest frequency in a complex wave form; pitch note

what is the fundamental and what is it referred to in music

the frequencies higher than the fundamental in a complex sound

what are overtones

the harmonics and their relative levels produced by an instrument or sound source

what is timbre

by the frequency response of equipment; mic placement

how can tonal balance (timbre) be changed and what technique can you use to do so

the amplitude of the sound changes during the duration of any sound in nature

what is a sound envelope

attack, decay, sustain, release

what are the four stages of the sound envelope

the time it takes for a sound to reach its full amplitude when first sounded

what is attack

how fast the sound levels off to a sustain after the attack

what is decay

how long the sound continues after the decay

what is sustain

how long it takes to fade out at the end of the sound

what is release

dB; a unit of measurement of the amplitude of a sound wave or audio signal

what are decibels

SPL; the amount of pressure in a given area that is caused by sound

what is sound pressure level

dB SPL

what is the unit of measurement for amplitude of sound waves

the wattage or power of an audio signal

what does dBm refer to

changes the wattage or amount of power

what does moving a fader on a mixer do

volatge or pressure behind the flow

what does dBv refer to

a volume unit meter that measures the level of an audio signal

what is a VU meter

digital

what is a VU meter not commonly used for

peak program meter; purely electronic/software device that measures audio signal levels and used instead of VU meter for digital

what is PPM

the ear closest to the sound source will receive the loudest sound

what is interaural intensity differences

sound arrives at each ear at different times; the one closest hears it first

what is interaural time differences

ridges on our outer ear that create very small time differences by reflecting sound into the ear canal off these ridges; determine which direction sound is coming from

what is the effects of the pinna and what does it help us do

direct sound, early reflections, and reverberations

what 3 cues tell us how large a room is and how far away the sound is coming from

sound that travels the shortest path and reaches ear first

what is direct sound

sounds that bounce off surfaces and arrive at our ears first

what are early reflections

sound reflections that arrive at the ear more than 50 ms after the direct reflections as a continuous melded sound, even though it is many different reflections

what is reverberation