frequency, pitch, tone and length february 12, 2014 thanks to chilin shih for making some of these...
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Frequency, Pitch, Tone and Length
February 12, 2014
Thanks to Chilin Shih for making some of these lecture materials available.
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Announcements• For Friday: Production Exercise #2 is due.
• at 5 pm
• On Friday, we will talk about the suprasegmental features of language:
• tone, accent, stress and quantity
• On Monday after the break: transcription exercise on tone.
• Yoruba and a mystery tone language!
• For today, let’s start off by doing something fun.
• …and then let’s dig deeper into acoustics.
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Pin
Fad
Fad
• How is sound transmitted through the air?
• Recall our bilabial trill scenario:
Acoustics: Basics
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What does sound look like?• Air consists of floating air molecules
• Normally, the molecules are suspended and evenly spaced apart from each other
• What happens when we push on one molecule?
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What does sound look like?• The force knocks that molecule against its neighbor
• The neighbor, in turn, gets knocked against its neighbor
• The first molecule bounces back past its initial rest position
initial rest positionCheck out some atomic bomb videos…
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What does sound look like?• The initial force gets transferred on down the line
rest position #1
rest position #2
• The first two molecules swing back to meet up with each other again, in between their initial rest positions
• Think: bucket brigade
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Compression Wave• A wave of force travels down the line of molecules
• Ultimately: individual molecules vibrate back and forth, around an equilibrium point
• The transfer of force sets up what is called a compression wave.
• What gets “compressed” is the space between molecules
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Compression Wave
area of high pressure
(compression)area of low pressure
(rarefaction)
• Compression waves consist of alternating areas of high and low pressure
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Pressure Level Meters• Microphones
• Have diaphragms, which move back and forth with air pressure variations
• Pressure variations are converted into electrical voltage
• Ears
• Eardrums move back and forth with pressure variations
• Amplified by components of middle ear
• Eventually converted into neurochemical signals
• We experience fluctuations in air pressure as sound
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Measuring Sound• What if we set up a pressure level meter at one point in the wave?
Time
pressure level meter• How would pressure change over time?
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Sine Waves• The reading on the pressure level meter will fluctuate between high and low pressure values
• In the simplest case, the variations in pressure level will look like a sine wave.
time
pressure
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Other Basic Sinewave concepts• Sinewaves are periodic; i.e., they recur over time.
• The period is the amount of time it takes for the pattern to repeat itself.
• The frequency is the number of times, within a given timeframe, that the pattern repeats itself.
• Frequency = 1 / period
• usually measured in cycles per second, or Hertz
• The peak amplitude is the the maximum amount of vertical displacement in the wave
• = maximum/minimum amount of pressure
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Complex Waves• When more than one sinewave gets combined, they form a complex wave.
• At any given time, each wave will have some amplitude value.
• A1(t1) := Amplitude value of sinewave 1 at time 1
• A2(t1) := Amplitude value of sinewave 2 at time 1
• The amplitude value of the complex wave is the sum of these values.
• Ac(t1) = A1 (t1) + A2 (t1)
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Complex Wave Example• Take waveform 1:
• high amplitude
• low frequency
• Add waveform 2:
• low amplitude
• high frequency
• The sum is this complex waveform:
+
=
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Other Examples• 480 Hz tone
• 620 Hz tone
• the combo = ?
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Fundamental Frequency• The fundamental frequency of a complex wave is the frequency at which the complex wave repeats itself.
• = greatest common denominator of frequencies of component waves.
• Greatest common denominator =
• largest number that two (or more) numbers can be divided by to yield an integer (whole number) value.
• Q: What’s the fundamental frequency of a complex wave consisting of 600 Hz and 800 Hz tones?
• How about one with 120 Hz and 150 Hz tones?
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Linguistically Speaking• In speech, the fundamental frequency of voiced sounds is based on the rate at which the vocal folds open and close.
• The wave set up by the vocal folds is a complex wave.
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Complex Wave Visual• Combination of 100 Hz and 300 Hz wave.
• Voicing sort of looks like this, but it’s even more complex:
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Why Should You Care?• The modulation of fundamental frequency in speech can have linguistic meaning.
• Tone
• Pitch Accent
• Stress
• Intonation
• Since this modulation can occur (relatively) independently of the stream of vowel and consonant segments in speech…
• these linguistic properties are often referred to as suprasegmentals.
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Suprasegmentals• Suprasegmentals are phonetic features of speech which are “above the segment”
• Tone/Accent/Intonation
• Quantity
• Stress
• “Suprasegmental features are established by a comparison of items in a sequence.” --Ilse Lehiste (1970)
• Suprasegmental features are always defined in a relative manner.
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Where Tone Comes FromHere’s a waveform for my vowel :
• The acoustic shockwave of each opening of the vocal folds shows up as a vertical bar in the waveform.
• A “voicing bar”
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Voicing Bar Close-up
Individual glottal pulses
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Voicing bars, really close up
• The fundamental frequency of voicing can be calculated by measuring the period between glottal pulses.
• Voicing is a complex wave. (i.e., not sinusoidal)
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Voicing bars, really close up
• Frequency = 1 / period
• In this case, period = .01 seconds, so frequency = ?
period
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Pitch Tracks• Measuring the fundamental frequency (F0) at every step in a sound file yields a pitch track.
• Time on the x-axis.
• Fundamental frequency on the y-axis.
F0
time
I’d like to collect sea shells this after noon
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Just So You Know• Praat has an automatic pitch tracker.
• Check it out.
• It can be messed up by:
• voiceless sounds
• obstruents (stops, fricatives, affricates)
• Also, it can sometimes double or halve the correct fundamental frequency.
• I’ll spare you the technical reasons why.
• In general, though, it works well.