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

A method for decoding a sound signal, comprising:

• receiving a bitstream including sound signal encoding parameters in successive sound signal processing frames, wherein the sound signal encoding parameters include linear predictive (LP) filter parameters:
• decoding from the bitstream the sound signal encoding parameters including the LP filter parameters during the successive sound signal processing frames, and producing from the decoded sound signal encoding parameters an LP synthesis filter excitation signal, wherein decoding the LP filter parameters comprises, when switching from a first one of the frames using an internal sampling rate S1 to a second one of the frames using an internal sampling rate S2, converting LP filter parameters from the first frame from the internal sampling rate S1 to the internal sampling rate S2, and wherein converting the LP filter parameters from the first frame comprises:
• computing, at the internal sampling rate SI, a power spectrum of a LP synthesis filter using the received LP filter parameters;
• modifying the power spectrum of the LP synthesis filter to convert it from the internal sampling rate S1 to the internal sampling rate S2;
• inverse transforming the modified power spectrum of the LP synthesis filter to determine autocorrelations of the LP synthesis filter at the internal sampling rate S2;
• and using the autocorrelations to compute the LP filter parameters at the internal sampling rate S2;
• synthesizing the sound signal using LP synthesis filtering in response to the decoded LP filter parameters and the LP synthesis filter excitation signal;
• and
• wherein modifying the power spectrum of the LP synthesis filter to convert it from the internal sampling rate S1 to the internal sampling rate S2 comprises:
• if S1 is less than S2, extending the power spectrum of the LP synthesis filter based on a ratio between S1 and S2;
• if S1 is larger than S2, truncating the power spectrum of the LP synthesis filter based on the ratio between S1 and S2.

A device for encoding a sound signal, comprising:

• at least one processor;
• and
• a memory coupled to the processor and comprising non-transitory instructions that when executed cause the processor to:
• produce, in response to the sound signal, parameters for encoding the sound signal during successive sound signal processing frames, wherein (a) the sound signal encoding parameters include linear predictive (LP) filter parameters, (b) for producing the LP filter parameters when switching from a first one of the frames using an internal sampling rate S1 to a second one of the frames using an internal sampling rate S2, the processor is configured to convert the LP filter parameters from the first frame from the internal sampling rate S1 to the internal sampling rate S2, and (c) for converting the LP filter parameters from the first frame, the processor is configured to:
• compute, at the internal sampling rate S1, a power spectrum of a LP synthesis filter using the LP filter parameters,
• 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,
• use the autocorrelations to compute the LP filter parameters at the internal sampling rate S2, and
• encode the sound signal encoding parameters into a bitstream;
• and wherein the processor is configured to:
• extend the power spectrum of the LP synthesis filter based on a ratio between S1 and S2 if S1 is less than S2;
• and
• truncate the power spectrum of the LP synthesis filter based on the ratio between S1 and S2 if S1 is larger than S2.

A device for decoding a sound signal, comprising:

• at least one processor;
• and
• a memory coupled to the processor and comprising non-transitory instructions that when executed cause the processor to:
• receive a bitstream including sound signal encoding parameters in successive sound signal processing frames, wherein the sound signal encoding parameters include linear predictive (LP) filter parameters;
• decode from the bitstream the sound signal encoding parameters including the LP filter parameters during the successive sound signal processing frames, and produce from the decoded sound signal encoding parameters an LP synthesis filter excitation signal, wherein (a) for decoding the LP filter parameters when switching from a first one of the frames using an internal sampling rate S1 to a second one of the frames using an internal sampling rate S2, the processor is configured to convert the LP filter parameters from the first frame from the internal sampling rate S1 to the internal sampling rate S2, and (b) for converting the LP filter parameters from the first frame, the processor is configured to:
• compute, at the internal sampling rate SI, a power spectrum of a LP synthesis filter using the received LP filter parameters,
• 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 at the internal sampling rate S2, and
• synthesize the sound signal using LP synthesis filtering in response to the decoded LP filter parameters and the LP synthesis filter excitation signal, and wherein the processor is configured to:
• extend the power spectrum of the LP synthesis filter based on a ratio between S1 and S2 if S1 is less than S2;
• and
• truncate the power spectrum of the LP synthesis filter based on the ratio between S1 and S2 if S1 is larger than S2.