Acoustic structure of consonants1.

Acoustic structure of consonants
1. Revision of basic concepts

a) The source-filter model; quasi-periodic and aperiodic (noise) sources.

b) The filtering effect of the vocal tract, acting as a variable resonator.

c) The characterisation of vowel sounds by formants.

d) Other resonant sounds are also characterised by formants: sonorant consonants i.e. nasals, medial and lateral approximants. Obstruents - stops, fricatives and affricates - are characterised by a combination of intervals of noise, silence, and changing formant transitions.

2. Stops

a) In articulation, stops consist of:

i) if the stop is preceded by a vowel, a closing phase, or transition between the vowel and the stop;

ii) an interval of complete closure;

iii) an audible burst, as the closure is opened;

iv) in some stops, an interval of aspiration;

v) an interval of transitions from the stop into the following vowel or approximant, often overlapping with (iv).

b) Because of (ii), all stops have a period of silence. If the stop is fully voiced (e.g. some intervocalic voiced stops in English), there will be a low level of quasiperiodic energy during the closure.

c) The burst is very brief, with energy across the spectrum. Unreleased stops do not show a burst, of course.

d) Aspiration is a longer interval of noise, with a broad-band frequency distribution that varies with the place of articulation of the stop.

e) Prevocalic stops have a formant frequency pattern which changes in time for an interval after the release of the stop, during the early part of the vowel - the transition.

f) Postvocalic stops have similar (but 'mirror-image') formant frequency transitions at the end of the preceding vowel, as the stop closure is formed.

For the most part, (b-d) are acoustic realizations of the manner of articulation; (e-f) realize the place of articulation.

2.1. Acoustic details

a) Voicing. A low frequency voicing buzz is present in phonetically voiced sounds, seen on spectrograms as 'voice bar'. Also, in English, presence vs. absence of aspiration cues voicelessness vs. voicing, respectively.

b) Place of articulation. There are three major acoustic correlates:

(i) The spectrum of the burst:

Bilabials - energy predominantly from 600 - 800 Hz.

Alveolars - the energy is distributed across frequency range, more energy in higher areas of spectrum (4000 Hz and above).

Velars - there is a compact burst in lower to mid part of frequency range, typically about 1,800 - 2,000 Hz, but up to around 4,700 Hz.

Irrespective of other variations, bursts tend to show a strength hierarchy of voiceless aspirated > voiceless unaspirated > voiced.

(ii) Formant transitions and (iii) Loci: - Both the apparent origin and trajectory of first three formant transitions reflect articulatory movements, and are therefore considered crucial for stop recognition.

c) Post-vocalic stops: In post-vocalic position (VC sequences) the trajectories are the opposite of those in pre-vocalic stops, although these may be less clearly visible spectrograms in the case of voiceless stops.

3. Fricatives and affricates

a) Main features:

(i) frication noise -aperiodic spread of sound over part of spectrum

(ii) areas of 'anti-resonance' - where there is no energy. The frequency of these vary according to place of articulation.

b) Voicing. Again, phonetically voiced fricatives have low level voicing along with frication noise. Phonemically voiceless fricatives may have short period of aspiration before voicing onset in some languages.

c) Place of articulation. Two major acoustic features carry place distinctions:

(i) Formant transitions. Similar to those of stops. Labiodentals similar to labials, dentals similar to alveolars, though F2 locus higher.

(ii) Spectral envelope - mainly for sibilants, distribution of energy across spectrum shows:

Alveolars are characterised by random energy from approximately 2000 Hz, up to and above 8000 Hz. Peaks of energy at 4500 and 7500 Hz.

Post-alveolars have noise form about 2000 Hz - 6/7000 Hz. Peak at around 4000 Hz.

Both of the above have strong frication noise (sibilants). For non-sibilants, spectral features less distinctive.

Labiodentals and dentals both have flat spectra with a slight emphasis in high frequency energy.

Bilabials have relatively more energy in lower part of spectrum.

d) [h] is acoustically a voiceless vowel. It has a weak formant structure appropriate to following vowel, but with noise excitation rather than voicing.

e) Affricates have frication portions similar to the corresponding fricatives, preceded by stop-like 'silent' portion.


4. Nasals

a) As a class nasals share certain features. They are nearly always voiced, and they show a sudden change in formant structure from/to adjacent vowel (a 'fault transition').

Furthermore:

(i) Presence of nasal formants, the frequencies of which vary from speaker to spea

Hasil (Bahasa Indonesia) 1:

Akustik struktur konsonan1. revisi konsep-konsep dasar) model sumber-filter; kuasi periodik dan aperiodic sumber (kebisingan).b) penyaringan efek vokal, bertindak sebagai variabel resonator.c) karakterisasi suara vokal oleh formants.d) suara resonan lainnya juga ditandai oleh formants: konsonan sonorant yaitu nasals, medial dan lateral approximants. Obstruents - berhenti, fricatives dan affricates - ditandai oleh kombinasi interval kebisingan, keheningan, dan mengubah formant transisi.2. berhenti) dalam artikulasi, berhenti terdiri dari: i) jika berhenti diawali dengan huruf vokal, tahap penutupan atau transisi antara vokal dan berhenti; II) selang waktu penutupan lengkap; III) audible meledak, sebagai penutupan dibuka; IV) di beberapa halte, interval aspirasi; v) selang waktu transisi dari halte ke vokal berikut atau hampir, sering tumpang tindih dengan (iv).b) karena (ii), berhenti di semua perhentian memiliki periode keheningan. Jika berhenti sepenuhnya disuarakan (misalnya beberapa intervocalic disuarakan perhentian dalam bahasa Inggris), akan ada tingkat rendah kuasiperiodik energi selama penutupan.c) ledakan sangat singkat, dengan energi di seluruh spektrum. Berhenti dirilis tidak menunjukkan burst, tentu saja.d) aspirasi itu lagi interval noise, dengan distribusi yang luas-band frekuensi yang bervariasi dengan tempat artikulasi Stop.e) prevocalic berhenti memiliki pola frekuensi formant yang berubah dalam waktu untuk interval setelah rilis berhenti, selama bagian awal vokal - transisi.f) postvocalic berhenti memiliki transisi frekuensi formant mirip (tapi 'gambar cermin') di akhir vokalnya, penutupan berhenti dibentuk.Untuk sebagian besar, (b-d) adalah akustik realisasi dari cara artikulasi; (e-f) menyadari tempat artikulasi.2.1. akustik rincian) menyuarakan. Sebuah frekuensi rendah yang menyuarakan buzz hadir dalam suara fonetik disuarakan, terlihat pada spectrograms sebagai 'suara bar'. Juga, dalam bahasa Inggris, kehadiran vs ketiadaan aspirasi isyarat voicelessness vs menyuarakan, masing-masing.b) tempat artikulasi. Ada tiga berkorelasi akustik yang utama: (i) spektrum meledak: Bilabials - energi terutama dari 600-800 Hz. Alveolars - energi didistribusikan di seluruh rentang frekuensi, lebih banyak energi di tempat-tempat yang lebih tinggi spektrum (4000 Hz dan di atas). Velars - ada ledakan kompak di bawah bagian pertengahan rentang frekuensi, biasanya sekitar 1.800-2.000 Hz, tetapi sampai sekitar 4.700 Hz. Terlepas dari variasi lain, semburan cenderung untuk menunjukkan hirarki kekuatan afrikat disedot > afrikat unaspirated > disuarakan. (ii) formant transisi dan (iii) lokus:-baik jelas asal dan lintasan pertama tiga formant transisi mencerminkan gerakan gangguan artikulasi, dan karena itu dianggap penting untuk pengakuan berhenti.c) Post-vocalic stops: In post-vocalic position (VC sequences) the trajectories are the opposite of those in pre-vocalic stops, although these may be less clearly visible spectrograms in the case of voiceless stops.3. Fricatives and affricatesa) Main features: (i) frication noise -aperiodic spread of sound over part of spectrum (ii) areas of 'anti-resonance' - where there is no energy. The frequency of these vary according to place of articulation.b) Voicing. Again, phonetically voiced fricatives have low level voicing along with frication noise. Phonemically voiceless fricatives may have short period of aspiration before voicing onset in some languages.c) Place of articulation. Two major acoustic features carry place distinctions: (i) Formant transitions. Similar to those of stops. Labiodentals similar to labials, dentals similar to alveolars, though F2 locus higher. (ii) Spectral envelope - mainly for sibilants, distribution of energy across spectrum shows: Alveolars are characterised by random energy from approximately 2000 Hz, up to and above 8000 Hz. Peaks of energy at 4500 and 7500 Hz. Post-alveolars have noise form about 2000 Hz - 6/7000 Hz. Peak at around 4000 Hz. Both of the above have strong frication noise (sibilants). For non-sibilants, spectral features less distinctive. Labiodentals and dentals both have flat spectra with a slight emphasis in high frequency energy. Bilabials have relatively more energy in lower part of spectrum.d) [h] is acoustically a voiceless vowel. It has a weak formant structure appropriate to following vowel, but with noise excitation rather than voicing.e) Affricates have frication portions similar to the corresponding fricatives, preceded by stop-like 'silent' portion.4. Nasalsa) As a class nasals share certain features. They are nearly always voiced, and they show a sudden change in formant structure from/to adjacent vowel (a 'fault transition').Furthermore: (i) Presence of nasal formants, the frequencies of which vary from speaker to spea