Spectral Analysis

1
Spectral Analysis
February 14, 2012
2
Friendly Reminders

• ToBI homeworks to hand back.
• Extra credit ToBI Production exercise will be
  posted later today.
• due after the break
• Mid-term is on Thursday!
• On the Tuesday after the break, well be back in
  the Craigie Hall lab.
• Korean stops exercise
• Todays goal start to learn where spectrograms
  come from.
• http//sakurakoshimizu.blogspot.com/

3
Voice Quality Summary
AT LT MC Flow Modal moderate varies moderat
e med. Tense high varies high high Creaky high
low high low Whisper low N/A high med. Brea
thy low varies low high Falsetto high high hi
gh low
4

• Last but not least, Korean makes an interesting
  distinction between emphatic (or fortis)
  obstruents and unaspirated and aspirated (lenis)
  obstruents.

5
Whats going on here?

• A variety of things occur during the articulation
  of fortis consonants in Korean.
• Glottis is not open as wide (during closure) as
  in lenis stops.
• Voicing begins more quickly after stop release
• Increased airflow in fortis stops.
• Higher F0 after stop release.
• Vocal folds are more tense than in lenis stops.
• greater medial compression
• squarer glottal waveform

6
Back to the Source

• Modal voicing (by me)

• Note completely closed and completely open
  phases are both actually quite short.
• Also closure slope is greater than opening
  slope.
• Q Why might there be differences in slope?

7
A Different Kind of Voicing

• The basic voice quality in khoomei is called
  xorekteer.

• Notice any differences in the EGG waveforms?
• This voice quality requires greater medial
  compression of the vocal folds.
• ...and also greater airflow

8
Why Should You Care?

• Remember that the most basic kind of sound wave
  is a sinewave.

pressure
time

• Sinewaves can be defined by three basic
  properties
• Frequency, (peak) amplitude, phase

9
Complex Waves

• It is possible to combine more than one sinewave
  together into 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)
• Note a harmonic is simply a component sinewave
  of a complex wave.

10
Complex Wave Example

• Take waveform 1
• high amplitude
• low frequency

• Add waveform 2
• low amplitude
• high frequency

• The sum is this complex waveform

11
Another Perspective

• Sinewaves can also be represented by their power
  spectra.
• Frequency on the x-axis
• Intensity on the y-axis (related to peak
  amplitude)
• Waveform Power Spectrum

12
Putting the two together
Waveform Power Spectrum




harmonics
13
More Combinations

• What happens if we keep adding more and more
  high frequency components to the sum?

14
A Spectral Comparison
Waveform Power Spectrum
15
Whats the Point?

• Remember our EGG waveforms for the different
  kinds of voice qualities

• The glottal waveform for tense voice resembles a
  square wave.
• ? lots of high frequency components (harmonics)

16
Whats the point, part 2

• A modal voicing EGG looks like

• It is less square and therefore has less high
  frequency components.
• Although it is far from sinusoidal...

17
Whats the point, part 3

• Breathy and falsetto voice are more
  sinusoidal...
• And therefore the high frequency harmonics have
  less power, compared to the fundamental frequency.

18
Lets Check em out

• Head over to Praat and check out the power
  spectra of
• a sinewave
• a square wave
• a sawtooth wave
• tense voice
• modal voice
• creaky voice
• breathy voice

19
Spectral Tilt

• Spectral tilt drop-off in intensity of higher
  harmonics, compared to the intensity of the
  fundamental.

20
The Source

• The complex wave emitted from the glottis during
  voicing
• The source of all voiced speech sounds.
• In speech (particularly in vowels), humans can
  shape this spectrum to make distinctive sounds.
• Some harmonics may be emphasized...
• Others may be diminished (damped)
• Different spectral shapes may be formed by
  particular articulatory configurations.
• ...but the process of spectral shaping requires
  the raw stuff of the source to work with.