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phonetics (spring term) > 1. acoustic phonetics > Flashcards

1. acoustic phonetics Flashcards

1
Q

What is sound?

A

Sound is variation in air pressure detectable by human ear

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2
Q

How do sound waves propagate?

A

Sound propagation involves the movement of pressure differences, not the flow of medium itself.

The air particles are compressed (increase in air pressure) and stretched / rarefied (decrease in air pressure).

Air molecules are moved when we speak by:

They are compressed and stretched / through the repetition of compression and rarefaction

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3
Q

What does an acoustic waveform represent?

A

An acoustic waveform is a visual record of pressure fluctuations over time at a particular point in space:

  • Compression (increased pressure)
  • Rarefaction (decreased pressure)
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4
Q

What is the difference between a periodic and aperiodic sound wave?

A

Periodic waves: have a pattern that repeats itself regularly (__after a period of time, T)

Aperiodic waves: no systematic repetition

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5
Q

What is fundamental frequency?

A

Fundamental frequency (F0) is the frequency with which the overall pattern repeats itself**. It is the **lowest.

It corresponds to the pitch that we hear

Fundamental frequency is number of repetitions in a unit time (1/T), measured in Hertz (Hz)

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6
Q

What is frequency of a periodic sound wave? In which units is it measured?

A

Fundamental frequency is number of repetitions in a unit time (1/T), measured in Hertz (Hz)

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7
Q

What is duration of a periodic sound wave? In which units is it measured?

A

Duration of a single cycle T, measured in seconds/ms

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8
Q

What is amplitude of a periodic sound wave?

A

Pressure fluctation from normal atmopsheric pressure

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9
Q

What are the types of periodic sound waves and how do they differ?

A
  1. SIMPLE PERIODIC WAVES
    • Simple periodic waves / sine waves stem from simple harmonic motion such as pendulum. Pure sine waves are rare in speech
  2. COMPLEX PERIODIC WAVES – SPEECH WAVES
    • Composed of at least two sine waves - have energy at different frequencies.
    • Composed of a fundamental component [lowest frequency - fundamental frequency (F0) + higher-frequency components (harmonics). Frequencies of harmonics are all multiples of the fundamental

Properties

  • Duration of a single cycle T, measured in seconds or milliseconds (thousandths of a second). The duration of a single cycle is called the period
  • Frequency f/F is number of repetitions per unit time (1/T), measured in Hertz (Hz) ; number of cycles per second
  • Amplitude A / intensity: pressure fluctuation from normal atmospheric pressure. increased A ⟹ louder; decreased A ⟹ quieter
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10
Q

What is a harmonic and how does it relate to fundamental frequency?

A

Higher frequencies are known as harmonics. They have varying amounts of energy

They are multiples of the fundamental

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11
Q

Give examples of periodic sounds.

A

(Speech sound waves can be either periodic or aperiodic)

Periodic waves are those which have a pattern that repeats in regular fashion, as in voiced sounds in modal speech (e.g., [z], [m], [a])

  • Vowels
  • Approximants (/w j l r/)
  • Nasals (m n ŋ)
  • Voiced obstruents [plosives, fricatives, affricates]
    • voiced plosives: b d g
    • voiced fricatives: v ð z ʒ
    • voiced affricates: dʒ

Complex periodic (several components/sound waves)

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12
Q

Give examples of aperiodic sounds.

A

(Speech sound waves can be either periodic or aperiodic)

Aperiodic waves do not repeat regularly and include voiceless sounds (e.g., [f], [s], [h])

  • Voiceless obstruents [plosives, fricatives, affricates]
    • voiceless plosives: p t k
    • voiceless fricatives: f θ s ʃ (+ h)
    • voiceless affricates: tʃ
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13
Q

What is a formant?

A

Formants are the most prominent frequencies of a sound, which correspond to the resonance frequencies of the vocal tract configuration for that sound.

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14
Q

On spectrograms, what do formants look like?

A

Dark horizontal bars

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15
Q

What does a spectrum of a complex periodic sound represent?

A
  • Strongest amplitude + lowest frequency = fundamental frequency
  • Other components = harmonics (all weaker than the fundamental frequency)
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16
Q

Explain the phenomenon of resonance.

A

Resonance: the oscillation of an object along with**, and **in reaction to, another object

17
Q

What is a resonant frequency?

A

An object’s preferred frequency with which it oscillates when set in vibration (vibrates best at)

18
Q

How does the resonant frequency of an object depend on its shape and size?

A

Shape

  • Wide or long objects vibrate slowly – they have low resonant frequency
  • Narrow or short objects vibrate quickly – they have high resonant frequency

Size:

  • Big or heavy objects vibrate slowly – they have low resonant frequency
  • Small or light objects vibrate quickly – they have high resonant frequency

Resonant frequency of an object depends on its size and shape and on what it is made of

  • Big, wide, long or heavy objects vibrate slowly – they have low resonant frequency
  • Small, narrow, short or light objects vibrate quickly – they have high resonant frequency
19
Q

What are the effects of resonance?

A

Resonance has two-fold effect:

  • Amplitudes are increased at the natural/resonant frequencies of the system, ie. it works as a resonator
  • Amplitudes at other frequencies are absorbed, decreased, ie. the system works as a filter
20
Q

Explain source-filter theory of speech production.

A

The source-filter theory describes speech production as a two stage process involving:

  1. Generation of a sound source, with its own spectral shape and spectral fine structure
  2. Which is then shaped or filtered by the resonant properties of the vocal tract
    • Supraglottal vocal tract filters the source = certain harmonics are dampened whilst others are enhanced
    • Filtering is a result of VT resonances – some components of the voice source are enhanced because they correspond to resonance frequencies of (part of) the vocal tract
    • These resonance frequencies change when VT shape changes, leading to different sound qualities
    • In vowels, these resonances are called formants: F1, F2, F3

The speech signal is generated by vocal tract filtering of a source sound.

It emphasises the independence of the source of the sound from the filter that shapes it

21
Q

According to the source-filter theory of speech production, what are the sources of speech sounds?

A
  1. Vocal fold vibration / voicing
  2. Turbulence noise produced at the glottis/in the larynx (incl. whisper), eg. sound [h]
  3. Turbulence noise generated elsewhere (fricatives, plosive releases, fricative part of an affricate) [can be at all locations above the glottis - remember the IPA chart!]
22
Q

According to the source-filter theory of speech production, what are the filters?

A

Most of the filtering of a source spectrum is carried out by that part of the vocal tract anterior to the sound source

The vocal tract filter always includes some part of the oral cavity and can also, optionally, include the nasal cavity (depending upon whether the velum is open or closed)

Examples:

  • Source: glottis // Filter: everything above glottis (supraglottal)
  • Source: postalveolar region [for postalveolar sound] // Filter: postalverolar forward
  • Source: laryngeal // Filter: entire supraglottal (supralaryngeal) vocal tract
23
Q

Name three types of visual representations of speech.

A
  1. Waveforms
    • Time (x-axis) + amplitude (y-axis)
    • 2D graph [how amplitude changes in time]
  2. Spectrum
    • Frequency (x-axis) + amplitude (y-axis)
    • Single moment in time [spectrum of sound: exactly which component is present]
  3. Spectrogram
    • Time (x-axis) + frequency (y-axis) + amplitude (darkness/colour of grey scale)

SPECTROGRAM:

  1. Time, usually seconds or milliseconds (.001s)
    • Time runs from left to right [so you can see that words differ in length]
  2. Frequency, in Hertz (Hz)
    • Frequency of the components is shown on vertical scale
  3. Amplitude, in decibels (dB) / intensity
    • Shown by degree of darkness - dark bands for concentration of energy at particular frequencies ⟹ showing source + filter characteristics of speech
24
Q

Which features of speech are represented on a waveform?

A
  • Time (x-axis)
  • Amplitude (y-axis)
25
Q

Which features of speech are represented on a spectrum?

A
  • Frequency (x-axis)
  • Amplitude (y-axis)
26
Q

Which features of speech are represented on a spectrogram?

A
  • Time (x-axis)
  • Frequency (y-axis)
  • Amplitude(darkness/colour of grey scale) (z-scale)
  • A way of representing the changes of spectral characteristics of speech over time
  • Spectrograms can utilize a range of different filter settings, most usually a narrow band filter of 45 Hz, which gives maximum frequency information, or a broad band filter of 300 Hz, which maximizes temporal information
27
Q

On a spectrogram, what are the most important properties of vowels?

A
  • Periodic sounds – vertical striations
  • Formants seen as dark horizontal bars
    • F1 – tongue height (high – low F1)
    • F2 – back-front (back – low F2)
    • F3 - adds to quality distinctions (retroflexion of the tongue + lip rounding)
      • Rhoticised (retroflex tongue) ⟹ lower F3
      • Lip rounding ⟹ lower F3
  • Diphthongs (see movement of formants from first part to second)

HAS FORMANTS

28
Q

What are formant frequency variations?

A

Different speakers will have different formant frequency values for the same vowel

  • Male vocal tracts are longer than female ⇒ all formant frequencies are lower for males than for females
  • Relative values are important, eg. for all speakers F1 will be low and F2 high for [iː]
29
Q

On a spectrogram, what are the most important properties of fricatives?

A
  • Voiceless fricatives are aperiodic
  • Do not have formants in the way vowels do
  • But still have concentrations of energy at different frequencies (difference between [s] and [ʃ])
  • Voiced fricatives combine aperiodic and periodic:
    • Aperiodic hissing sound like voiceless fricatives
    • Periodic vibration of vocal folds (voicing bar)
30
Q

On a spectrogram, what are the most important properties of plosives?

A
  • Voiceless plosives begin with silence (complete closure)
  • Release of air causes explosive, brief, transient aperiodic noise
  • If plosive is aspirated, then the burst is followed by air rushing through vocal tract - aperiodic
  • Voiced plosives are periodic during vocal tract closure (although in English these have very little voicing)

Have to see whether there is hold + release phase & possibly aspiration!

b d g word initially can actually be quite similar to p t k after s in terms of voicing because [POA will be represented in other properties in vowels etc]

31
Q

On a spectrogram, what are the most important properties of nasals?

A
  • Periodic
  • Each of the nasals has a formant structure similar to that of a vowel, except that the bands are fainter and are in particular frequency locations that depend on the characteristic resonances of the nasal cavities (**similar to vowels but with less energy at higher frequencies)
  • Formants difficult to identify
  • Low F1
  • Air passes through nasal cavity
  • Antiresonance is a feature of nasal sounds, where some frequency bands are suppressed because of the coupling of 2 cavities (nasal to oral)
    • An antiformant is sometimes said to be in place 800-2000Hz
    • As if a formant was just deleted; some white-ish bits will be in that area

HAS FORMANTS

32
Q

On a spectrogram, what are the most important properties of affricates?

A
  • Acoustically complex
  • Voiceless affricates begin as plosives, in silence, followed by aperiodic release
  • Voiced affricates have periodic first part and mixed second part
33
Q

On a spectrogram, what are the most important properties of approximants?

A
  • Similar to vowels
  • Formants easy to identify (possibly except [l])

HAS FORMANTS

Other sounds:

  • Taps and flaps are usually voiced, seen like very brief voiced plosives
  • Trills are also usually voiced and are doubly periodic:
    • VF vibration
    • (much slower) vibration of one of the articulators
34
Q

What type of information can be found in formant transitions?

A

Formant transitions/“formant bending” occurs systematically at vowel starts following stops

  • Each formant seemed to begin from a particular locus and move into position
  • They hypothesised that it was the tongue position for the stop that determined the locus
  • It is especially noticeable for voiced plosives

As listeners we are not directly aware of formant transitions, but experiments have found that the transitions are important cues for the stops, even when removed from the signal

phonetics (spring term) (2 decks)

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