구름사이

참조 논문(2021년 논문) :  https://arxiv.org/pdf/2106.15561.pdf

Articulatory Synthesis ::

  - simulating the behavior of human articulator such as lips, tongue, glottis and moving vocal tract.

  -The speech quality by articulatory synthesis is usually worse.

Formant Synthesis ::

  - a set of rules that control a simplified source-filter model.

  - mimic the formant structure and other spectral properties of speech

  - an additive synthesis module and an acoustic model with varying parameters like fundamental frequency, voicing, and noise levels.

 - highly intelligible speech with moderate computation resources

 - well-suited for embedded systems

Concatenative Synthesis

  -  concatenation of pieces of speech that are stored in a database.

  - searches speech units to match the given input text, and produces speech waveform by concatenating these units together.

  - requires huge recording database in order to cover all possible combinations

  - less natural and emotional

Statistical Parametric Synthesis

   - first generate the acoustic parameters then recover speech from the generated acoustic parameters 

   - consists of three components: a text analysis module, a parameter prediction module (acoustic model), and a vocoder analysis/synthesis module (vocoder). 

   - text analysis module

       :    text normalization , grapheme-to-phoneme conversion , word segmentation, etc

       :  phonemes, duration and POS

   -  a parameter prediction module(Acoustic Model)

       :  The acoustic models (HMM based)

       :  the paired linguistic features and parameters (acoustic features)

          ::  acoustic features :: F0, spectrun, cepstrum..

   - vocoder analysis

   - 장점

       : 1) naturalness,  2) flexibility,  3) low data cost

   - 단점

      : lower intelligibility,  still robotic

cf.) 음성인식과 연결하면,   Feature Analysis, Acoustic Model, Search Algorithm.(outputs text )

Neural Speech Synthesis

  - early neural models ::  replace HMM for acoustic modeling. (3 components ) : DeepVoice 1/2 

  - directly generate waveform from linguistic features(2 components )  :  WaveNet 

  - some end-to-end models: Tacotron 1/2, Deep Voice 3, FastSpeech 1/2

       1. simplify text features.

       2. directly take  characters/phonme sequences as input,       

       3. simplify acoustic features with mel-spectrograms.

     ( 그림 1 참조.)

  - fully end-to-end ( directly generate waveform form text ) : ClariNet, FastSpeech 2s, EATS

==> high voice quality in terms of both intelligibility and naturalness,

      less requirement on human preprocessing and feature development