26. sound Flashcards
Sound energy def?
Travelling wave of air pressure changes
Continuous sounds aka…?
Pure tones
Pure tones/continuous sounds represented in what kind of wave?
Sin wave
2 phases of sin wave for pure tones (cont. sounds) ?
Compression & Rarefaction
Compression def? What does it look like on the wave?
High density, high pressure
Where molecules bump into each other
Upper part of the wave, the “peak”
Rarefaction def? What does it look like on the wave?
Low density, low pressure
Molecules aren’t bumping into each other (as much)
Lower part of wave, “valley”
How is a wave shown on a graph? What are the axes? (options…)
Y axis: air pressure
X axis:
- Time is most common
- Space (if you FREEZE time and measure from the origin of the sound expanding outwards/towards the ear)
3 physical dimensions of sound? What are their perceptual correlates?
- Frequency
- Amplitude
-
Waveform
–> Pure tone - simple sin wave
–> Complex sound - all bumpy, combination of a bunch of different pure tones
1a. Pitch (freq.)
2a. Loudness (amp)
3a. Timbre (waveform)
Wavelength def? (Is this super commonly used when discussing sounds?)
Time for ONE (1) cycle to be completed, from start to finish
NOT commonly used, much more common to use frequency
Frequency def? Unit?
NUMBER of cycles per second
Unit: Hertz (Hz)
Pitch def?
- the perceived highness or lowness of a sound
- perceptual correspondent to FRQ
Amplitude def?
- Difference b/tw the max and min sound pressure in a sound wave
- physical aspect of sound –> related to the perceptual aspect of loudness
Loudness def? depends on…?
- how intense or quiet a sound seems
- perceptual correspondent to amp
- depends on amp AND frq
“Phase relations” –>
2 phases that exist for PURE tones within a complex sound?
In phase & out phase
In phase def?
When does it happen/ what does it look like/ what’s going on?
- both component waves are in the same “side” of the graph
- both compressing or both rarefacting at the same time
Out phase def?
When does it happen/ what does it look like/ what’s going on?
- the component waves are NOT on the same “side” of the graph
- doing opposite things
- kinda cancel each other out
- can create little pulsations
- this part of the sound is what makes you feel like its NOT a pure tone
How do noise canceling headphones work?
- they produce noise that it out of phase with noise from the environment
- it cancels out, and you hear relative silence / quiet
decibel (dB) definition? SPL meaning?
dB SPL meaning??
- A physical unit used to measure sound amplitude
- Uses LOGS of micro-pascals to convert into reasonable numbers
- SPL = Sound Pressure Level
- means that its the agreed upon standard where:
–> Po is 20 micro-pascals
–> 0 dB is the threshold for adult human hearing of a 1,000 Hz tone
Fourier analysis def / what’s it for?
A mathematical procedure for decomposing a complex waveform into a collection of sine waves with various frequencies and amplitudes.
What does a Fourier spectrum show? What does it look like? What are the axes?
- Shows the amplitudes at all frequencies that make up a complex waveform
- Looks like a BAR graph
X axis: Frq
Y axis: Amp
Fundamental frequency def?
- The frequency of the simple wave produced by the simplest back-and-forth motion
- also the lowest frequency component of a complex sound
Harmonics def? (where do they occur?) What is their numerical relationship to fundamental frq?
- A second/third/etc. part of vibration that is an EXACT MULTIPLE of the fundamental frq.
- They occur in instruments that have strings
Harmonics example:
fundamental frq = 100 Hz
Give the first 2 harmonics. How much of the string is vibrating for each?
200 Hz –> 1/2 of the string
300 Hz –> 1/3 of the string
Harmonics:
- What does the Fourier spectrum look like? (general slope)
- What does this mean for the relationship between amp. and frq.?
- angles down, tail to the right
- As frq increases, the amp. decreases
^ general trend, not rule all of the time
Why do notes sound different on a flute, clarinet, and violin? What perceptual dimension of sound is affected?
- the relative strengths of all the harmonics are different
- this makes the timbre different
How is amplitude measured/specified? What units? What is the equation?
- PRESSURE
- pressure (therefore amp) is measured in dB SPL
- dB SPL = 20 log (P/po) –> (p null)
What is 0 dB?
Threshold for adult human hearing for a 1000 Hz tone
How to measure sound level of increasing sounds / noises?
- CAN’T add dB
- only add pressures
- log (x + y) = log(x) + log(y)
2 tones are played with the same amplitude, but they aren’t perceived as equally loud. Why does this happen?
- loudness depends on amp and frq
- we aren’t equally sensitive to all frqs
- sensitivity changes based on amp
Audibility curve def? What are the axes? What’s the general shape? Lowest range?
- shows minimum amplitude at which sounds can be detected at each frequency
- shape is a U ish / V ish curve
- lowest range is between 500-5000 Hz
- any 2 points would sound the same
x axis: frequency
y axis: dB SPL (amplitude)
Equal loudness contour def? What does graph look like? What are units and axes?
- curve shows the amplitude of tones at different frequencies that sound about equally loud
- Graph mirrors the audibility curve but moves higher up & flattens as it moves up
- Units = PHONS
x axis: frequency
y axis: dB SPL (amplitude)
Phon def? Accounts for…?
- unit of loudness
- the loudness of a tone in phons is numerically equal to the amplitude of a 1,000 Hz tone that sounds equally loud–> ie if the loudness = 50 phons, then an equally loud tone of 1,000 Hz would have an amp of 50
- accounts for differential sensitivity to frequencies
Timbre def?
- perceptual correlate of waveform
- differences in sound quality due to things other than pitch and loudness
- for complex sounds, mainly due to relative amplitudes of overtones / harmonics
What 2 things does timbre depend on?
- relative strengths of harmonics
- “tone envelope”
“Tone envelope” –> 2 components? Meaning? ex from class?
Attack rate and decay rate
Rate of the rise and decline of a note
Piano played backwards (diff. tone envelope) doesn’t sound like a piano anymore. Sounds like bagpipes
