Acoustics

=Acoustics=

(Well, more specifically, acoustic phonetics)
 Standard III-B

**Why is this important?** : speech perception and production are issues that we deal with


 * people create different sound waves, and yet, we still understand it, although it may require other clues, such as context (example foreign accent)

Some stuff about SOUND in general
(now for some physicsish and scientificish stuff about sound) Defn: vibrating mechanical form of energy giving rise to an auditory sensation Occurs in a wave form Occurs only when there is: Molecules have mass and electrical charges so they like to stay an equal distance from each other... so the disturbance travels through the medium The energy moves, the air molecules stay in relatively the same place, but a wave is formed by compressions and rarefactions __compressions:__ when the molecules get pushed too close together __rarefaction:__ when the molecules push apart and then they are too far apart air pressure is higher during compressions...see below ==== Why is this important? because sound wave compressions and rarefactions (rapid changes in air pressure) push in and suck out the ear drum which is how we hear (for more details on the process of hearing, see the Audiology page) ==== __a pure tone__: the simplest sound, sound that occurs only at one frequency. It is a perfect sine wave (wait a minute, who said we had to remember trigonometry) therefore, the period and amplitude of adjacent waves are exactly the same  Why is this important?  because audiologists use pure tones to test hearing ( (yes, man can make pure tones, but they do not occur in nature) ) **
 * an energy source
 * a vibrating sound source
 * an elastic medium
 * __period__: the time for a sound wave to go by, measured peak to peak
 * __amplitude:__ the height measured from the x axis to the peak, this is a measure of acoustic energy, the taller the amplitude, the more energy!
 * Pure tone does not occur in nature so....

a note about frequency, pitch, intensity and loudness....it's all about perception __frequency:__ the number of cycles per second (a measureable phenomenon) __pitch__: human perception of how high or low a sound is __intensity:__ a measureable amount of acoustic energy--the amplitude of a sound wave l__oudness:__ the perception of how loud something is

in a complex periodic sound, there is a fundamental frequency wave (F0), and then harmonics (H2, H3, H4 etc) which bisect that wave __Resonance__: when one vibrating body causes vibration in another body __Natural resonant frequenc__y is the frequency that something resonates most easily at A container with a certain shape, will make sounds that are at the same frequency as its natural resonant frequency louder, and it will attenuate sounds that are not at that frequency. __formants__ are concentrations of acoustic energy which reflect the resonant frequencies of the container (which frequencies were strengthened)

Now some stuff about SOUND as it relates more specifically to speech and hearing
in the adult male vocal tract, the shape of it serves as a resonator that amplifies frequencies at 500, 1500, and 2500 Hz. Remember that these frequencies are called formants. Each phoneme we here is really a combination of formants. The formants for the vowel "uh" or schwa just happen to be 500, 1500, and 2500 Hz... isn't that interesting! So then how do we get different formants for different sounds? Change the shape of the resonantor! By making changes in tongue placement for instance, we can find all of the formants for the vowels. F1 values reflect tongue height F2 values reflect tongue placement (forward or back) Here is a chart of the formants for some vowels

So now you're thinking... Wow, how do we know all this stuff? the answer is the Spectrograph A __spectrograph__ analyzes sound/breaks down sound into it's component parts and creates a picture/diagram representation called a __spectrogram__ of frequency vs time, amplitude is indicated by darkness. Cool stuff huh? and the spectrograph was invented in the 1940s

Here are two spectrograms of the phrase "we owe you" a) shows the phrase stated typically (with __coarticulation__ as a factor) b) show the phrase with each word stated distinctly, with space between each word you can see the little connecting lines (or transitions) in a) that illustrate the movement of the articulators (notice transitions are apparent in the F2 formant)

On spectrograms, stop consonants, look like a brief silent period followed by a burst of acoustic energy (aperiodic noise) the frequency is dependent on what consonant it is, for example, for p/b the oral cavity is more open so it has a lower frequency than k/g Stops can be identified by: 1) frequency 2) the transitions 3) voice onset time (the time between the onset of the consonant and the onset of vocal fold vibration)

Fricatives are longer durations of aperiodic sound and can be identified by: 1) frequency (s/z is a higher frequency than sh/zh) 2) loudness (s is louder than f) 3) transitions 4) voice onset time

Nasals 1) frequency (from different oral cavity shape) 2) F2 transitions 3) nasal resonance (which causes a low F1) 4) vocal fold vibration for whole time

Semivowels 1) transitions

In general, vowels tend to be louder than consonants the loudest sound is /a/ and the softest sound is /th/

Wow that is neat, but Why is this important? it helps us to understand speech as an auditory phenomenon. this information should help us when dealing with clients with hearing loss as well as clients with articulation disorders

You should also know about place, manner, and voicing for each phoneme. (example: /b/ is a bilabial, stop, that is voiced) if you don't... [|Here is that cool University of Iowa phonetics site] You may also find more information on the Articulation-Phonology page

Useful VOCAB Bilabials (lips) b, p, m Labial-dentals (lips-teeth) f, v Lingua-dentals AKA Interdentals (tongue-teeth) th, TH Lingua-alveolars (tongue-alveolar ridge) t, d, s, z, n Lingua-palatals (tongue-hard palate) sh, zh Lingua-velars (tongue-soft palate) k, g, ng
 * Place of articulation**
 * Glottals (vocal folds) h **

__Plosives/stops:__ produced by complete obstruction of air flow. Plosive release followed by air flow through glottis. __Fricatives__: produced by partial closure of the vocal tract and sustained air flow. __Affricates__: produced by complete closure, followed by sustained air flow through point of articulation. __Glides__: changes in resonance patterns produced by changing position of articulators during production of sound. __Nasals:__ produced by permitting air to flow through nasal cavity. **Other terms to describe manner of production** __Obstruents__: characterized by obstructed air flow, complete or partial. Most consonants are obstruents. __Sonorants:__ sounds that are made with relative open oral cavity (consonant sonorants are called 'semi-vowels'). __Stridents:__ sounds produced by directing the air flow against a surface, such as the back of the teeth, to create noticeable friction. /f/, /v/, /s/, /z/ 'sh', 'zh', 'ch', and 'j'. __Sibilants__: subset of stridents characterized by high frequency sound. /s/, /z/, 'sh', 'zh', 'ch', and 'j'. __Laterals__: characterized by air flow around the sides of the tongue. /l/. __Liquids__: /l/ and /r/ sounds. Term liquid is used to indicate open production (no friction) **
 * Manner of production**

<span style="background-color: rgb(255, 255, 0); color: rgb(0, 128, 0);">//Another way to think about it which relates back to the scientific stuff near the top of the page// Gunnar Font's Source-Filter Theory of speech production There are three sound sources: a) phonation- vocal folds vibrate, creating quasiperiodic sound b) stop- burst of aperiodic sound c) fricative- longer duration aperiodic sound Each phoneme can be described by combinations of a, b, and c. <span style="color: rgb(255, 0, 255);">Example: a+b=voiced stops, c=voiceless fricatives, a+b+c=voiced affricate __cognate pairs__: sounds that differ only by voicing <span style="color: rgb(255, 0, 255);">example: b/p, s/z, k/g __Phone__: any sound that can be produced by the human vocal tract __Phoneme__: a family of sounds in a language with similar characteristics (place, manner, voicing) __Allophone:__ a specific member of a phoneme family, a variation of a phoneme that is still accepted as being that phoneme. This is often affected by __coarticulation__. For example, the /s/ in "see" and in "Sue" are acoustically different, but still considered the same phoneme. (<span style="color: rgb(128, 0, 128);">Okay now really try saying these /s/ sounds without finishing the rest of the word, you'll see/hear the difference)

References: [] http://www.geocities.com/agihard/mohl/mohl_language_substance.html http://www.images.google.com Hegde, M.N. (2001). __Introduction to Communicative Disorders, 3rd Edition__. Austin, TX: Pro-Ed Inc. Hoodin, R. (2005). Lecture notes from SPSI 332: Acoustic Phonetics, Eastern Michigan University