The Source

January 26, 2010

Voice Quality ReviewAT LT MC Flow

Modal moderate varies moderate med.

Creaky high low high low

Breathy low varies low high

Some Leftovers1. Louie Armstrong: ventricular voice

2. This American Life: Alix Spiegel

3. The Shining & “Tony”

4. Steve Sklar’s high pitch tense voice

• “Tense voice” maintains the high medial compression and adductive tension of creaky voice…

• But adds higher airflow

• And longitudinal tension can vary.

• There are a couple more voice quality options…

Tense Voice• Tuvan throat singing (khoomei): xorekteer voice

• The high medial compression squares off the glottal waveform on both top and bottom.

4. Whispery Voice• When we whisper:

• The cartilaginous glottis remains open, but the ligamental glottis is closed.

• Air flow through opening with a “hiss”

• The laryngeal settings:

1. Little or no adductive tension

2. Moderate to high medial compression

3. Moderate airflow

4. Longitudinal tension is irrelevant…

Nodules• One of the more common voice disorders is the development of nodules on either or both of the vocal folds.

• nodule = callous-like bump

• What effect might this have on voice quality?

Last but not least• What’s going on here?

• At some point, my voice changes from modal to falsetto.

5. Falsetto• The laryngeal specifications for falsetto:

1. High longitudinal tension

2. High adductive tension

3. High medial compression

• Contraction of thyroarytenoids

4. Lower airflow than in modal voicing

• The results:

• Very high F0.

• Very thin area of contact between vocal folds.

• Air often escapes through the vocal folds.

Falsetto EGG

• The falsetto voice waveform is considerably more sinusoidal than modal voice.

Voice Quality SummaryAT LT MC Flow

Modal moderate varies moderate med.

Creaky high low high low

Tense high varies high high

Breathy low varies low high

Whisper low N/A high med.

Falsetto high high high low

• Check out Mel Blanc one last time…

Sine Waves!• “Sinusoidal” = resembling a sine wave.

• A sine wave is a purely mathematical concept;

• it reflects the change in position--in one dimension only--of a point moving around a circle.

• Check it out: http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=148

time

amplitude (displacement)

Waveforms• Remember: a waveform plots amplitude on the y axis against time on the x axis.

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.

• A cycle is one repetition of the acoustic pattern.

• 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 (or minimum) amount of pressure

Sine vs. Complex• Periodic motions are not necessarily sinusoidal; they can often exhibit a complex pattern of repetition.

• A (perhaps familiar) example--my modal voicing EGG:

• Note: complex waves may have the same properties that sine waves do (period, frequency, peak amplitude)…

• But we need to know more than this to describe them completely.

Combinatorics• Q: What do complex waves have that sine waves do not?

• A: More than one sine wave.

• Any time you add two different sinewaves together, you get 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)

• Let’s play with an example in Praat…

Complex Wave Visual• Take waveform 1:

• high amplitude

• low frequency

• Add waveform 2:

• low amplitude

• high frequency

• The sum is this complex waveform:

+

=

Pin

Fad

Fad

• Recall our trill scenario:

Why does this matter?

• Air emanates from the vocal tract in a series of short, sharp bursts.

• = it’s periodic.

Sound: The Microscopic View• Air consists of floating air molecules

• Normally, the molecules are suspended and evenly spaced apart from each other (and in three dimensions)

• What happens when we push on one molecule?

A B C D E F

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 position

A B C D E F

A B C D E F

What does sound look like?• The initial force gets transferred on down the line

rest position #1

rest position #2

• Note: the initial push has been transferred from A to B to C…

• Also note: molecules A and B swing back to meet up with each other again, in between their initial rest positions

• Think: bucket brigade

A B C D E F

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

A B C D E F

A B C D E F

Compression Wave

area of high pressure

(compression)area of low pressure

(rarefaction)

• Compression waves consist of alternating areas of high and low pressure

• We experience fluctuations in air pressure as sound.

A B C D E F

Wave Types• In a compression wave, the particles travel in the same direction as the wave being propagated.

• In a transverse wave, the particles travel perpendicularly to the propagation of the wave.

• Try the slinky experiment.

Source: http://paws.kettering.edu/~drussell/Demos/waves/wavemotion.html

More Visualization

• It is possible to convert a compression wave, like sound, into a transverse wave representation by using a pressure level meter.

Pressure Level Meters• Microphones

• Have diaphragms, which move back and forth with air pressure variations

• Pressure variations are converted into electrical voltage

• (Note: a speaker performs the opposite operation:

• it converts waveforms into air pressure variations.)

• Ears

• Eardrums move back and forth with pressure variations

• Amplified by components of middle ear

• Eventually converted into neurochemical signals

Importance!• Almost all of the sounds we hear are complex compression waves.

• E.g.: glottal opening and closing cycles.

• The out-of-phase factor is reduced with thinner vocal folds.

• i.e., the glottal cycle becomes more sinusoidal

An Interesting Fact• Remember: adding different sine waves together results in a complex periodic wave.

• This complex wave has a frequency which is the greatest common denominator of the frequencies of the component sine waves.

• Greatest common denominator =

• biggest number by which you can divide both frequencies and still come up with a whole number (integer).

• Q: if I add together sine waves of 300 Hz and 500 Hz, what is the frequency of the resulting complex wave?

• A: 100 Hz.

Well, that’s weird.• Why is this so?

• Think: smallest common multiple of the periods of the component waves.

• Both component waves are periodic

• i.e., they repeat themselves in time.

• The pattern formed by combining these component waves...

• will only start repeating itself when both waves start repeating themselves at the same time.

• Example: 3 Hz sinewave + 5 Hz sinewave

For Example• Starting from 0 seconds:

• A 3 Hz wave will repeat itself at .33 seconds, .66 seconds, 1 second, etc.

• A 5 Hz wave will repeat itself at .2 seconds, .4 seconds, .6 seconds, .8 seconds, 1 second, etc.

• Again: the pattern formed by combining these waves...

• will only start repeating itself when they both start repeating themselves at the same time.

• i.e., at 1 second

3 Hz

5 Hz

.33 sec. .66 1.00

.20 .40 .60 .80 1.00

Combination of 3 and 5 Hz waves

(period = 1 second)

(frequency = 1 Hz)

1.00

Tidbits• Important point:

• Each component wave will complete a whole number of periods within each period of the complex wave.

• Comprehension question:

• If we combine a 6 Hz wave with an 8 Hz wave...

• What should the frequency of the resulting complex wave be?

• To ask it another way:

• What would the period of the complex wave be?

6 Hz

8 Hz

.17 sec. .33 .50

.125 .25 .375 .50

Combination of 6 and 8 Hz waves

(period = .5 seconds)

(frequency = 2 Hz)

.50 sec. 1.00

Fourier’s Theorem• Joseph Fourier (1768-1830)

• French mathematician

• Studied heat and periodic motion

• His idea:

• any complex periodic wave can be constructed out of a combination of different sine waves.

• The sinusoidal (sine wave) components of a complex periodic wave = harmonics

The Dark Side• Fourier’s theorem implies:

• sound may be split up into component frequencies...

• just like a prism splits light up into its component frequencies

• Also: sine waves effectively function as the atoms of sound.

Spectra• One way to represent complex waves is with waveforms:

• y-axis: air pressure

• x-axis: time

• Another way to represent a complex wave is with a power spectrum (or spectrum, for short).

• Remember, each sinewave has two parameters:

• amplitude

• frequency

• A power spectrum shows:

• intensity (based on amplitude) on the y-axis

• frequency on the x-axis

Two PerspectivesWaveform Power Spectrum

+ +

= =

harmonics

Example• Go to Praat

• Generate a complex wave with 300 Hz and 500 Hz components.

• Look at waveform and spectral views.

• And so on and so forth.

Fourier’s Theorem, part 2• The component sinusoids (harmonics) of any complex periodic wave:

• all have a frequency that is an integer multiple of the frequency of the complex wave.

• This is equivalent to saying:

• all component waves complete an integer number of periods within each period of the complex wave.

• Note: the frequency of the complex wave is known as its fundamental frequency.

• …to contrast it with the frequencies of the component (harmonic) waves.