Method of and means for variable-rate coding of LPC parameters

An apparatus for minimizing the amount of information sent to characterize a voice signal that has been divided into frames of equal times and for which parameters of linear predictive coding have been determined for each of a plurality of the frames, the apparatus comprising:

• (a) means for storing parameter values of a predetermined number of frames;
• (b) means for determining interpolated values resulting from linear interpolation between a parameter value of a first frame and a parameter value of a frame of the predetermined number;
• (c) means for comparing the interpolated values with the parameter values at frames between the first frame and the frame of the predetermined number to obtain compared values;
• (d) means for testing the compared values against a predetermined threshold;
• (e) means for transmitting the predetermined number and the parameter value of the frame of the predetermined number when no comparison exceeds the threshold;
• (f) means for reducing the predetermined number by one to obtain a reduced number when a comparison exceeds the predetermined threshold;
• (g) means for testing the reduced number for equality with the number of the first frame;
• (h) means for substituting the reduced number for the predetermined number when the reduced number is unequal to the number of the first frame;
• and
• (i) means for transmitting a parameter value of the frame of the reduced number.

An apparatus for minimizing the amount of information sent to characterize a signal that has been divided into frames of equal times and for which parameters of linear predictive coding have been determined for each of a plurality of the frames, the apparatus comprising:

• (a) means for storing and cycling parameter values;
• (b) means for storing and cycling quantized parameter values;
• (c) means for storing, cycling and releasing coded quantized parameter values;
• (d) means for determining an interpolation step size, the means connected to the means for storing and cycling quantized parameter values;
• (e) means for determining an interpolated value of a parameter, the means connected to the means for storing and cycling quantized parameter values and to the means for determining an interpolation step size;
• (f) subtracting means connected to the means for determining an interpolated value and to the means for storing and cycling parameter values, the subtracting means obtaining a difference between an interpolated value and a parameter value;
• and
• (g) means connected to the subtracting means, to the means for storing, cycling, and releasing coded quantized parameter values, and to a threshold for comparing a subtracted value with the threshold and controlling release of a coded quantized parameter value if the subtracted value exceeds the threshold.