CVSD to LPC conversion using noise tolerant analysis

Due to the increasing sophisitication and decreasing cost of digital hardware, an all-digital speech communication network is being considered for implementation. Subject to bandwidth limitations, present plans call for both 16 Kilobit Continuously Variable Slope Delta Modulation (CVSD) as well as 2.4 Kilobit Linear Predictive Coding (LPC) terminals. Hence the conversion of CVSD to LPC and vice versa arises naturally in this environment. This paper will focus on the CVSD to LPC conversion problem. After a brief discussion of the component system environments, a structure for the format conversion system will be proposed. Since previous work has shown that pitch and voicing decisions can be made on the CVSD observations, the presentation will focus on the identification of LPC predictor coefficients from the noisily observed CVSD data. The remainder of the paper centers on this and the coefficient correction problem, and a new class of linear estimators is shown to yield conditionally unbiased estimates of the LPC coefficients in both noisy and noiseless environments.