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Ch2-Speech_Coding

Ch2-Speech_Coding - Speech Processing Speech Coding Veton...

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Unformatted text preview: Speech Processing Speech Coding February 11, 2012 Veton Këpuska 2 Speech Coding Definition: Speech Coding is a process that leads to the representation of analog waveforms with sequences of binary digits . Even though availability of high-bandwidth communication channels has increased, speech coding for bit reduction has retained its importance. Reduced bit-rates transmissions required for cellular networks Voice over IP Coded speech Is less sensitive than analog signals to transmission noise Easier to: protect against (bit) errors Encrypt Multiplex, and Packetize Typical Scenario depicted in next slide (Figure 12.1) February 11, 2012 Veton Këpuska 3 Digital Telephone Communication System February 11, 2012 Veton Këpuska 4 Categorization of Speech Coders Waveform Coders: Used to quantize speech samples directly and operate at high-bit rates in the range of 16-64 kbps (bps - bits per second) Hybrid Coders Are partially waveform coders and partly speech model-based coders and operate in the mid bit rate range of 2.4-16 kbps. Vocoders Largely model-based and operate at a low bit rate range of 1.2-4.8 kbps. Tend to be of lower quality than waveform and hybrid coders. February 11, 2012 Veton Këpuska 5 Quality Measurements Quality of coding can is viewed as the closeness of the processed speech to the original speech or some other desired speech waveform. Naturalness Degree of background artifacts Intelligibility Speaker identifiability Etc. February 11, 2012 Veton Këpuska 6 Quality Measurements Subjective Measurement: Diagnostic Rhyme Test (DRT) measures intelligibility. Diagnostic Acceptability Measure and Mean Opinion Score (MOS) test provide a more complete quality judgment. Objective Measurement: Segmental Signal to Noise Ratio (SNR) – average SNR over a short-time segments Articulation Index – relies on an average SNR across frequency bands. February 11, 2012 Veton Këpuska 7 Quality Measurements A more complete list and definition of subjective and objective measures can be found at: J.R. Deller, J.G. Proakis, and J.H.I Hansen, “Discrete-Time Processing of Speech”, Macmillan Publishing Co., New York, NY, 1993 S.R. Quackenbush, T.P. Barnwell, and M.A. Clements, “Objective Measures of Speech Quality. Prentice Hall, Englewood Cliffs, NJ. 1988 Statistical Models February 11, 2012 Veton Këpuska 9 Statistical Models Speech waveform is viewed as a random process....
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Ch2-Speech_Coding - Speech Processing Speech Coding Veton...

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