Part1 speech basics
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This document provides an overview of speech signal fundamentals, including its generation, classification, and modeling techniques. It discusses the linear time-invariant (LTI) and linear time-variant (LTV) models used to understand speech production, as well as the characteristics of phonemes and the various speech sound categories. Key concepts like pitch detection and the role of the vocal tract in shaping speech signals are also highlighted.
Part1 speech basics
- 1. Unit 6 Speech Signal DR MINAKSHI PRADEEP ATRE PVG’S COET & GKPIM PUNE
- 2. References Book: Speech and Audio Processing by Dr Shaila Apte madam Pdf document: http://cs.haifa.ac.il/~nimrod/Compression/Speech/S1Basics2010.pdf For speech samples: https://www.signalogic.com/index.pl?page=speech_codec_wav_samples
- 3. Contents Speech: 1. Basics of speech signal and its features 2. LTI representation of speech signal 3. LTV representation of speech signal 4. Estimation of fundamental frequency 5. identification of voiced and unvoiced speech 6. and noise removal
- 4. Speech Speech signal is generated by nature Naturally occurring so random in nature Necessary to understand the generalized human speech production Simple linear time invariant (LTI) model for speech production Inherently time varying nature of speech Introduction to linear time variant (LTV) model of speech Speech type: consonants, fricatives Voiced and unvoiced (V/UV) speech
- 5. Speech Production Mechanism: Pipelines Model Vocal Tract
- 6. Vocal Tract Vocal tract is the cavity between the vocal cords and the lips, and acts as a resonator that spectrally shapes the periodic input, much like the cavity of a musical wind instrument. ƒ Simple model of a steady-state vowel regards the vocal tract as a linear time-invariant (LTI) filter with a periodic impulse-like input.
- 7. What is Speech signal? Created at the Vocal cords, travels through the Vocal tract, and produced at speakers mouth Gets to the listeners ear as a pressure wave Non-Stationary, but can be divided to sound segments which have some common acoustic properties for a short time interval Two Major classes: Phonemes (Vowels and Consonants)
- 8. Phonemes The basic sounds of a language (e.g. "a" in the word "father“) are called phonemes A typical speech utterance consists of a string of vowel and consonant phonemes whose temporal and spectral characteristics change with time In addition, the time-varying source and system can also nonlinearly interact in a complex way: our simple model is correct for a steady vowel, but the sounds of speech are not always well represented by linear time-invariant systems !
- 9. Vowel Production In vowel production, air is forced from the lungs by contraction of the muscles around the lung cavity Air flows through the vocal cords, which are two masses of flesh, causing periodic vibration of the cords whose rate gives the pitch of the sound Resulting periodic puffs of air act as an excitation input, or source, to the vocal tract
- 10. Typical Vowels
- 11. Speech Production A sound source excites a (vocal tract) filter ◦ Voiced: Periodic source, created by vocal cords ◦ Unvoiced: Aperiodic and noisy source Pitch is the fundamental frequency of the vocal cords vibration (also called F0) followed by 4-5 Formants (F1 - F5) at higher frequencies Natural frequencies occur at odd multiples of 500 Hz. These resonant frequencies are called formants. Vowel Adult Male Adult Female F1 F2 F3 F1 F2 F3 (i) 255 2330 3000 340 2610 3210 (u) 290 940 2180 390 995 2585 (ae) 735 1625 2465 950 1955 2900 Typical formant frequencies for selected vowels in Hz This table shows the three values
- 12. LTI Model for speech production Impulse Train Generator (Glottis) Random Signal Generator Impulse Response of Vocal Tract Generated Speech Impulse train generator is used as an excitation signal when a voiced segment is produced VOWEL e.g. “a” Basic Assumption: source of excitation and the vocal tract systems are independent Periodic
- 13. LTI Model for speech production Impulse Train Generator (Glottis) Random Signal Generator Impulse Response of Vocal Tract Generated Speech Random Signal Generator is used as an excitation signal when an unvoiced segment is produced CONSONANTS e.g. “s” LTI model is used for a short segment of speech @10 ms for which we can assume the parameters of vocal tract remain constant Random
- 14. Nature of Speech Signal Speech is generated by components like vocal cords and vocal tracts It’s not possible to generate a speech signal on its own Speech is random signal Speech has/ can have infinite features (story of an elephant and the blind people touching the elephant to identify and specify what the elephant looks like) So it’s a complex problem Uttering the different words is possible because of humans can change the resonant modes of the vocal cavity and can also stretch the vocal cords to some extent for modifying the pitch period for different vowels And that’s why we have the linear time-varying (LTV) model
- 15. Linear Time-varying Model: Speech production Impulse Train Generator Random Signal Generator Impulse Response of Vocal Tract Generated Speech Amplitude Pitch period is variable Impulse response is variable
- 16. Speech Sound Categories Periodic (Sonorants, Voiced) Noisy (Fricatives , Un-Voiced) Impulsive (Plosive) Example: In the word “shop,” the “sh,” “o,” and “p” are generated from a noisy, periodic, and impulsive source, respectively
- 17. Frequency Range Speech: Pitch frequency: ◦ male ~ 85-155 Hz; ◦ female ~ 165-255 Hz; Singer’s vocal range: from bass to soprano: 80 Hz-1100 Hz
- 18. Pitch Pitch period: The time duration of one glottal cycle Pitch (fundamental frequency): The reciprocal of the pitch period. Remember: we will calculate the pitch for voiced segment
- 19. Pitch Detection The pitch period and V/UV decisions are elementary to many speech coders Many methods for the calculation: ◦ Autocorrelation function ◦ ZCR
- 20. Features or categorization of speech sound Speech sounds are studied and classified from the following perspectives: 1) The nature of the source: periodic, noisy, or impulsive, and combinations of the three 2) The shape of the vocal tract 3) The time-domain waveform, which gives the pressure change with time at the lips output 4) The time-varying spectral characteristics revealed through the spectrogram
- 21. Spectrogram Time-varying spectral characteristics of the speech signal can be graphically displayed through the use of a tow-dimensional pattern Vertical axis: frequency, Horizontal axis: time The pseudo-color of the (red: high energy ) pattern is proportional to signal energy The resonance frequencies of the vocal tract show up as “energy bands” Voiced intervals characterized by striated appearance (periodically of the signal) Un-Voiced intervals are more solidly filled in
- 23. Most common Manner of articulation Plosive, or oral stop, where there is complete occlusion (blockage) of both the oral and nasal cavities of the vocal tract, and therefore no air flow. Examples include English /p t k/ (voiceless) and /b d g/ (voiced) Nasal stop, where there is complete occlusion of the oral cavity, and the air passes instead through the nose. The shape and position of the tongue determine the resonant cavity that gives different nasal stops their characteristic sounds. Examples include English /m, n/ Fricative, sometimes called spirant, where there is continuous frication (turbulent and noisy airflow) at the place of articulation. Examples include English /f, s/ (voiceless), /v, z/ (voiced), etc
- 24. Most common Manner of articulation Sibilants are a type of fricative where the airflow is guided by a groove in the tongue toward the teeth, creating a high-pitched and very distinctive sound. These are by far the most common fricatives. English sibilants include /s/ and /z Affricate, which begins like a plosive, but this releases into a fricative rather than having a separate release of its own. The English letters "ch" and "j" represent affricates Trill, in which the articulator (usually the tip of the tongue) is held in place, and the airstream causes it to vibrate. The double "r" of Spanish "perro" is a trill. Approximant, where there is very little obstruction. Examples include English /w/ and /r/. Lateral approximants, usually shortened to lateral, are a type of approximant pronounced with the side of the tongue. English /l/ is a lateral.
- 25. Time for MATLAB Program
- 26. THANK YOU