Linear Predictive Encoder Format Modification.
ITT DEFENSE COMMUNICATIONS DIV NUTLEY N J
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As a result of the initial testing of the Linear Predictive Encoder hardware, it was determined that the overall speech quality at the data rate of 2400 Hz was significantly degraded from that obtained at 3600 Hz while no noticeable difference was detected in comparison of operation at 3600 Hz with that at 4800 Hz. Both the transmit filter parameters and excitation signal parameters are coded for transmission using the same format for all three rates. The various data rates are obtained by varying only the data frame update interval. The 72 bit data frame is update at rates of 15, 20, and 30 msec. corresponding to the data rates of 4800, 3600, and 2400 Hz respectively. It was therefore concluded that 30 msec updates were not satisfactory for tracking variation of the input speech. The goal was to determine a non-linear coding format for the filter parameters which allows 2400 Hz operation at a lower update rate and does cause noticeable degradation due to additional quantizing error.
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