ENGLISH PHONETICS AND PHONOLOGY 6SPEECH ANALYSIS: ACOUSTIC PHONETICS

INTRODUCTIONACOUSTIC PHONETICS is the scientific analysis of speech based on what we hearIts also known as instrumental phoneticsAcoustic phonetics focuses on the sound that we hear rather than the way the sound is produced or articulated.All speech sound are nothing more than sound wave and sound energy.

SPEECH WAVESLadefoged(2001:6) states that speech sounds are variations in air pressure that occur very rapidly one after another- complex wave formsAs one speaks, one causes the air particles to vibrate which results in variation in air pressure.Thus Baart(1999) states that sound consists of a series of small, rapid fluctuations of air pressure.These fluctuations from the speakers mouth affect the air pressure in adjacent locations traveling right to a listeners ear.The ear converts these vibrations into electrochemical signals, which are interpreted by the brain as sound.

The fluctuations or sounds can be captured and converted into speech wave graphsThis graph represents the air pressure variations on the vertical dimension and time on the horizontal dimension.The speech wave graph reveals a complex wave with several major and minor peaks over a duration of less than 50 milliseconds.The speech waves fluctuate going up and down capturing the variation in air pressure and resemble a wave- speech wave

WavelengthAmplitudeThe left to right dimensions represents time or duration of the sound segment or utterance.The bottom to top dimension represents air pressure- amplitude/loudness of the speech sound. The time taken to complete a single wave length or a cycle is the period.The frequency is the number of complete waves that pass through a point in one second (Hertz)

DurationThe duration of a speech segment is the length of time taken to utter the segment,A speech wave graph can be divided into segments that correspond to the consonant and vowel sounds that make up the utteranceFrom these graphs the duration of each of the segment and also the entire word can be calculated.In general, the vowels are longer than the consonants.

AmplitudeThe amplitude of the speech wave corresponds to the loudness of the sound.Loud sounds have larger amplitude than softer sound.In general, vowels are loudest sound as they form the peak or nucleus of a syllable.Nasal and liquids can also have relatively large amplitudes.Stop consonants have small amplitudes.

CLASSIFICATION OF SPEECH WAVESThe four groups of speech sounds are;

Silence (no sound; occurs as a part of a plosive consonant and also in speech pauses)- silence wavePlosion ( a sudden flow of air due to the build up and subsequent release of a pressure difference)- burst waveFriction noise (turbulence due to the air that is forced through a narrow constriction)- random waveVoice (repetitive opening and closing of the vocal chords)- periodic wave(Baart, 1999)

SilenceSeen as a straight line/absence of fluctuation over a stretch of timeBecause little air pressure / variation in air pressureCommon occurrence- when?Baart (1999) notes that short period of silence occurs when voiceless plosives, [t] occurs between 2 vowels- attack

Burst- Most noticeable in the aspiration of initial voiceless plosive sounds such as [p], [b], and [t].It normally extends over a short duration before higher amplitude waves- [p]-patRandom waveNo regular patternCaused by turbulent airflow due to partial obstruction to the air streamFricatives sounds normally produce random waves- [z] [zoo]

WAVE FORMS OF THE ENGLISH VOWELSThe vowels are very prominent in a speech graph because;Their overall amplitude is bigger than the othersTheir duration is also longer than the othersThe shape of the wave is more jagged as compared to the consonants

SPECTOGRAMS OF THE ENGLISH VOWELSThe spectogram is needed to show a more detailed analysis to identify and distinguish vowels.The spectogram represents the variation in a sound spectrum over time and the spectograph is the print out of the sounds producedThe spectrum is produced through a Fourier transformation of the speech waveIts another visual representation of the sounds based on the separation of the different frequencies of the speech wave.

The x axis of the spectrum shows the frequency in Hertz and the y axis shows the duration in time. (speech wave; x-duration/time, y-amplitude)Ladefoged(1993) points out that different vowels have different spectrumsThe most important acoustic feature of regular, voiced vowels are the frequencies of their formants- their first 2 or 3.What are formants?

What is a formant?A formant is a concentration of acoustic energy around a particular frequency in the speech wave.Each formant relates to a resonance in the vocal tract.In a spectogram, these formants appear as dark bands.The darker they are the more energy and the more audible the sound.In coloured spectograms, the various shade of darkness can be seen as yellowish to red bands,The frequencies of the formants of the English vowels can differ between individuals.The frequencies for man is lower than that of a woman because the average female vocal tract is smaller and so is the resonance cavities for womenSmaller cavities have higher resonance frequencies

POSITION OF VOWELS (YULE)

FrontCentralBack/i//I//////e/ //HighMidLow/u////c//a/F1 100Hz/Div

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2200 1800 1400 1000 F2(400Hz/Div) F1 correlates with the vowel height; low F1-close vowel, high F1- open vowelF2 correlates with the vowel being a back or front vowel; high F2- front vowel, low F2 back vowel

ENGLISH PLOSIVESThe difference between the plosives and vowel speech waves is the existence of a silent period at the start of the wave.This is followed by a regular up and down wave pattern before a burst at the end of the sound segment.The irregular waves are due to the sudden release of air in the plosives.Voiced plosives, however, might not indicate the burst clearly as it may merge with the onset of the following vowel.The phenomena of aspiration in the voiceless plosive [p] in the words initial position such as pat as opposed to an unaspirated sound at the end of a word tap is also apparentAspiration corresponds to a burst of air just before the vowel.

ENGLISH FRICATIVESThe voiceless fricatives [s] is characterised by a random waveThe overall amplitude of the wave is clearly smaller than the vowel following it.The voiced fricative [z], the speech wave is also a random wave with is in line to the friction noise.The regular pattern at the end of the sound segment is consistent with the phonation caused by the vibrating vocal chords.

ENGLISH NASALSNasal consonants [m], [n], show a periodic wave pattern that is very similar to that of vowels, thus distinguishing them becomes difficult.The distinguishing factor is in the amplitude since the vowel is usually louder than the consonants.Baart(1999) notes that the wave structure of the nasal is smoother as compared to the wave structure of the vowel

ENGLISH APPROXIMANTSThe speech waves of the two approximants [w] and [j] as well as two liquids [r] and [l].They have very similar wave forms to the nasals as they have periodic waves.All the two nasals have increasing amplitude with smaller amplitude at the start increasing getting larger at the end.Difficult to distinguish between the two approximants due to the similarity in the way they are produced.

SEGMENT BOUNDARIESA segment boundary is where one sound begins and the other ends.In natural conversation, it may be difficult as speakers move fast from one position to another.However it is still possible, as the speakers move from one position to another, the sound (speech wave) that is produced changes.Thus the exact locations of the boundaries is not necessary, as long as they are roughly correct.Knowing what to look for and the possible speech waves of the different segment as they are presented are a great help in determining various segment boundaries