Lecture 15_fall_2010

Lecture 15_fall_2010 - Digital Speech Processing Digital...

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Unformatted text preview: Digital Speech Processing Digital Speech Processing— ecture 15 ecture 15 Lecture 15 Lecture 15 Speech Coding Methods Based Speech Coding Methods Based on Speech Waveform on Speech Waveform Representations and Speech Representations and Speech Models Models—Uniform and Non Uniform and Non- niform Coding Methods niform Coding Methods 1 Uniform Coding Methods Uniform Coding Methods Analog Analog-to to-Digital Conversion Digital Conversion ampling and Quantization) ampling and Quantization) (Sampling and Quantization) (Sampling and Quantization) 2 Class of “waveform coders” can be represented in this manner formation Rate formation Rate Information Rate Information Rate aveform coder information rate , Waveform coder information rate, of the digital representation of the signal, w I i ( ) / , defined as: a w S x t I B F B T = ⋅ = 1 where is the number of bits used to B , represent each sample and is the umbe S F T = of samples/second 3 number of samples/second peech Information Rates peech Information Rates Speech Information Rates Speech Information Rates • Production level : – 10-15 phonemes/second for continuous speech – 32-64 phonemes per language => 6 bits/phoneme formation Rate 60 0 bps at the source – Information Rate =60-90 bps at the source • Waveform level – speech bandwidth from 4 – 10 kHz => sampling rate from 8 – 20 kHz – need 12-16 bit quantization for high quality digital coding – Information Rate =96-320 Kbps => more than 3 orders of magnitude difference in Information Rates between the production and waveform levels 4 Speech Analysis/Synthesis Systems Speech Analysis/Synthesis Systems • Second class of digital speech coding systems: o analysis/synthesis systems o model-based systems ybrid coders o hybrid coders o vocoder (voice coder) systems • Detailed waveform properties generally not preserved o coder estimates parameters of a model for speech production 5 o coder tries to preserve intelligibility and quality of reproduction from the digital representation Speech Coder Comparisons Speech Coder Comparisons peech parameters (the chosen representation) are • Speech parameters (the chosen representation) are encoded for transmission or storage • analysis and encoding gives a data parameter vector • data parameter vector computed at a sampling rate much lower than the signal sampling rate • denote the “frame rate” of the analysis as F fr • total information rate for model-based coders is: B F ⋅ • where B c is the total number of bits required to represent the parameter vector m c f r I B F = 6 Speech Coder Comparisons Speech Coder Comparisons • waveform coders characterized by: • high bit rates (24 Kbps – 1 Mbps) • w complexity low complexity • low flexibility • analysis/synthesis systems characterized by: • low bit rates (10 Kbps – 600 bps) 7 • high complexity • great flexibility (e.g., time expansion/compression) Introduction to Waveform Coding Introduction to Waveform Coding...
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This note was uploaded on 12/29/2011 for the course ECE 259 taught by Professor Rabiner,l during the Fall '08 term at UCSB.

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Lecture 15_fall_2010 - Digital Speech Processing Digital...

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