LP Filter Parameter Conversion for Multi-Rate Frame Switching
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Solution Overview
Problem
Existing LP-based codecs face challenges in seamlessly switching between frames with different internal sampling rates, particularly in multi-rate coders, due to issues related to LP filter transition, memory of the synthesis filter, and adaptive codebook.
Innovation Solution
A method and device for converting LP filter parameters by computing the power spectrum of the LP synthesis filter at the initial sampling rate, modifying it to match the target sampling rate, and using autocorrelations to determine the LP filter parameters at the new rate, without the need for re-sampling the past synthesis signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complete LP analysis is performed at both encoder and decoder for sampling rate conversion, then sampling rate transition accuracy is improved, but computational complexity increases significantly
Solution Approach 1:
The patent extracts only the necessary components for sampling rate conversion. Instead of performing complete LP analysis at both encoder and decoder, it extracts and transmits only the LP filter parameters from the encoder, which are then used at the decoder to convert between sampling rates. This selective extraction reduces computational complexity while maintaining transition accuracy.
Solution Approach 2:
The patent performs LP filter parameter computation and sampling rate conversion in advance at the encoder side before transmission. The decoder receives pre-processed parameters that are already optimized for the target sampling rate, eliminating the need for complex real-time analysis at the decoder and reducing overall computational complexity.
2Productivity
If LP filter parameters are converted using power spectrum modification and autocorrelation, then conversion efficiency is improved, but parameter transformation complexity increases
Solution Approach 1:
The patent changes the domain in which LP filter parameter conversion is performed. By transforming parameters from the time domain to the frequency domain (power spectrum), modifying the spectrum for the target sampling rate, and then transforming back via autocorrelation, it achieves efficient sampling rate conversion. This parameter domain transformation simplifies the conversion process compared to direct time-domain methods.
3Manufacturing precision
If multi-rate coding is implemented with different sampling rates, then audio quality is improved, but switching between rates becomes problematic
Solution Approach 1:
The patent implements dynamic sampling rate switching capability. The system can operate at different sampling rates (e.g., 16 kHz and 48 kHz) and seamlessly transition between them by using the same LP filter parameter conversion mechanism. The encoder and decoder can adaptively adjust the sampling rate based on transmission conditions while maintaining audio quality through consistent parameter transformation methods.
Data Source
AI summary
Methods, an encoder and a decoder are configured for transition between frames with different internal sampling rates. Linear predictive (LP) filter parameters are converted from a sampling rate S1 to a sampling rate S2. A power spectrum of a LP synthesis filter is computed, at the sampling rate S1, using the LP filter parameters. The power spectrum of the LP synthesis filter is modified to convert it from the sampling rate S1 to the sampling rate S2. The modified power spectrum of the LP synthesis filter is inverse transformed to determine autocorrelations of the LP synthesis filter at the sampling rate S2. The autocorrelations are used to compute the LP filter parameters at the sampling rate S2.