Speech Communications Chapter 7

Speech Communications  The Nature of Speech    Criteria for Evaluating Speech    Components of Speech Communication System    Synthesized Speech  

The Nature of Speech 1/2  發聲 : 呼吸系統, Articulators  Types of Speech Sound  Phoneme ( 音素 ) − shortest segment of speech if change → meaning change if change → meaning change  分類 : 母音 (vowel), 子音 (consonant) 雙母音 (diphthongs) 雙母音 (diphthongs)  Phoneme →Syllable →Word → Sentence

The Nature of Speech 2/2  Depicting Speech  Waveform, Spectrum  Sound spectrogram Fig 8-1 Fig 8-1 Fig 8-1  Intensity of Speech  Average intensity (speech power): 母音＞子音  Intelligibility: 子音較重要  Frequency Composition of Speech  低頻 : 男＞女 Fig 8-2 Fig 8-2 Fig 8-2  Shouting: frequency 上升

Criteria for Evaluating Speech  Speech Intelligibility ( 能解度 )  方法 − Repeat 呈現的聲音 − 回答問題  Test − Nonsense syllables − Isolated words (phonetically balanced, PB) − Sentences  Speech quality (Naturalness)  Preference

Components of Speech Communication System  Speaker  Message  Transmission System  Noise  Hearer

Components of Speech Communication System  Speaker  Enunciation ( 清晰的聲音 )  Superior Speakers − Longer syllable duration − Greater intensity − More total time with speech sounds − Frequencies varied 1/7

Components of Speech Communication System  Message  Phoneme Confusion − DVPBGCET, FXSH, KJA, MN − Avoid single letters, Word-spelling alphabet  Word Characteristics − Familiar words − Long words 2/7

Components of Speech Communication System  Message  Context Features − Sentence: meaningful ＞ nonsense − Set size: 字多＜字少 Fig 7-3 Fig 7-3 Fig 7-3 − Guidelines  用較少的字  Standard sentence  Avoid short word  Familiarize user 3/7

Components of Speech Communication System  Transmission System  Filtering (Frequency distortion) Fig 7-4 Fig 7-4 Fig 7-4 − High-pass: cutoff ＜ 600 Hz − Low-pass: cutoff ＞ 4000 Hz  Amplitude Distortion Fig Fig Fig − Peak clipping  Quality , Intelligibility ≈ − Center clipping  Intelligibility  − 提高 Intelligibility: Peak clipping  Amplify ( 子音 / 母音  ) 4/7

Components of Speech Communication System  Noise  Articulation Index (AI) Fig 7-7 Fig 7-7 Fig 7-7 − 1/3 octave, S-N, weighted sum − Intelligibility Fig 7-8 Tab 7-1 Fig 7-8Tab 7-1 Fig 7-8Tab 7-1  Preferred-Octave Speech Interference Level (PSIL) − Mean of 500, 1000, 2000 Hz (octave) − SIL: Mean of , ,... − Intelligibility (vs. distance) Fig 7-9 Fig 7-9 Fig 7-9 − Subjective rating Fig 7-10 Tab 7-2 Fig 7-10Tab 7-2 Fig 7-10Tab 7-25/7

Components of Speech Communication System  Noise  Preferred Noise Criterion Curve (PNC) Fig 7-11Fig 7-11 Tab 7-3 Tab 7-3 Fig 7-11Tab 7-3  Reverberation Fig 7-12 Fig 7-12 Fig 7-12 − Reverberation time: Decay 60 dB − Reverberation time   Intelligibility  6/7

Components of Speech Communication System  Hearer  Age Fig 7-13 Fig 7-13 Fig 7-13  Wearing of Hearing Protection 7/7

Synthesized Speech  種類  Uses  Performance  Preference  Guidelines

Synthesized Speech  種類  Synthesis by Analysis − Digitized human speech  compressed data format  compressed data format − 缺點 : 限於 encoded & stored Lack of coarticulation Lack of coarticulation  Synthesis by Rule − 缺點 : quality 較差