Methods, encoder and decoder for linear predictive encoding and decoding of sound signals upon transition between frames having different sampling rates

A device for interpolating LP filter parameters in a current sound signal processing frame following a previous sound signal processing frame, the previous frame using an internal sampling rate S1 and the current frame using an internal sampling rate S2 and defining a number of subframes, comprising:

• at least one processor;
• and
• a memory coupled to the processor and storing non-transitory instructions that when executed cause the processor to:
• provide LP filter parameters of the previous frame at the internal sampling rate S1;
• provide LP filter parameters of the current frame at the internal sampling rate S2;
• for converting the LP filter parameters of the previous frame from the internal sampling rate S1 to the internal sampling rate S2:
• compute, at the internal sampling rate S1, a power spectrum of an LP synthesis filter using the LP filter parameters of the previous frame;
• modify the power spectrum of the LP synthesis filter to convert it from the internal sampling rate S1 to the internal sampling rate S2;
• inverse transform the modified power spectrum of the LP synthesis filter to determine autocorrelations of the LP synthesis filter at the internal sampling rate S2;
• and
• use the autocorrelations to compute the LP filter parameters of the previous frame at the internal sampling rate S2;
• determine for at least one subframe of the current frame interpolated LP filter parameters by interpolation between the LP filter parameters of the current frame at the internal sampling rate S2 and the LP filter parameters of the previous frame converted from the internal sampling rate S1 to the internal sampling rate S2.