  In this paper, the approximation of the optimal compressor function using
spline function of the first-degree is done. For the companding quantizer
designed on the basis of the approximative spline function of the first-degree,
the support region is numerically optimized to provide the minimum of the total
distortion for the last segment. It is shown that the companding quantizer with
the optimized support region threshold provides the signal to quantization
noise ratio that is very close to the one of the optimal companding quantizer
having an equal number of levels.
