Ch12-Speech_Coding

Ch12-Speech_Coding - Speech Processing Speech Coding...

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Unformatted text preview: Speech Processing Speech Coding 2/13/12 Veton Kpuska 2 Speech Coding u Definition: n Speech Coding is a process that leads to the representation of analog waveforms with sequences of binary digits . u Even though availability of high-bandwidth communication channels has increased, speech coding for bit reduction has retained its importance. n Reduced bit-rates transmissions required for cellular networks n Voice over IP n Live TV n TV on Demand, etc. u Coded speech n Is less sensitive than analog signals to transmission noise n Easier to: u protect against (bit) errors u Encrypt u Multiplex, and u Packetize u Typical Scenario depicted in next slide (Figure 12.1) 2/13/12 Veton Kpuska 3 Digital Telephone Communication System 2/13/12 Veton Kpuska 4 Categorization of Speech Coders u Waveform Coders: n Used to quantize speech samples directly and operate at high-bit rates in the range of 16-64 kbps (bps - bits per second) u Hybrid Coders n Are partially waveform coders and partly speech model- based coders and operate in the mid bit rate range of 2.4-16 kbps. u Vocoders n Largely model-based and operate at a low bit rate range of 1.2-4.8 kbps. n Tend to be of lower quality than waveform and hybrid coders. 2/13/12 Veton Kpuska 5 Quality Measurements u Quality of coding can is viewed as the closeness of the processed speech to the original speech or some other desired speech waveform. n Naturalness n Degree of background artifacts n Intelligibility n Speaker identifiability n Etc. 2/13/12 Veton Kpuska 6 Quality Measurements u Subjective Measurement: n Diagnostic Rhyme Test (DRT) measures intelligibility. n Diagnostic Acceptability Measure and Mean Opinion Score (MOS) test provide a more complete quality judgment. u Objective Measurement: n Segmental Signal to Noise Ratio (SNR) average SNR over a short-time segments n Articulation Index relies on an average SNR across frequency bands. 2/13/12 Veton Kpuska 7 Quality Measurements u A more complete list and definition of subjective and objective measures can be found at: n J.R. Deller, J.G. Proakis, and J.H.I Hansen, Discrete-Time Processing of Speech, Macmillan Publishing Co., New York, NY, 1993 n S.R. Quackenbush, T.P. Barnwell, and M.A. Clements, Objective Measures of Speech Quality. Prentice Hall, Englewood Cliffs, NJ. 1988 2/13/12 Veton Kpuska 8 Statistical Models u Speech waveform is viewed as a random process....
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Ch12-Speech_Coding - Speech Processing Speech Coding...

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