Audio Resampling Interpolation for Low-Delay Codec Transitions
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Solution Overview
Problem
Current audio frequency signal processing methods, such as those used in resampling, face challenges in maintaining signal quality and reducing complexity, particularly when changing sampling frequencies, leading to issues like algorithmic delay and artifacts in transient signals.
Innovation Solution
A method for resampling audio frequency signals using an FIR-type filter with interpolation of order greater than one, calculating weighted averages of interpolation values from multiple intervals to produce interpolated samples, which complements restricted predictive decoding and transform coding in transition frames.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If polynomial interpolation is used for resampling, then delay is reduced and complexity is lowered, but aliasing artifacts appear at high frequencies
Solution Approach 1:
The patent divides the signal processing into two distinct stages: first applying polynomial interpolation to obtain initial resampled values with low delay, then applying correction terms derived from filter coefficients to eliminate aliasing artifacts. This segmentation allows each stage to optimize for its specific function without compromising the other.
Solution Approach 2:
The patent introduces correction terms as an intermediary mechanism between polynomial interpolation and final output. These correction terms, calculated using filter coefficients and neighboring signal values, act as a mediator that removes aliasing artifacts while preserving the low-delay advantage of polynomial interpolation.
2Reliability
If FIR filtering is used for resampling, then signal quality is maintained with linear phase, but algorithmic delay increases
Solution Approach 1:
The patent extracts only the essential anti-aliasing function from traditional FIR filtering, implementing it through correction terms rather than full convolution. This extraction removes the delay-causing extensive filtering while retaining the necessary signal quality preservation and artifact elimination.
Solution Approach 2:
Instead of applying complete FIR filtering which causes significant delay, the patent applies a partial action using correction terms that provide just enough anti-aliasing protection. This partial approach is sufficient for maintaining signal quality while avoiding the excessive delay of full convolutional filtering.
3Device complexity
If sub-band coding is used to reduce complexity, then coding complexity decreases, but transition between coding modes becomes problematic
Solution Approach 1:
The patent changes the resampling methodology parameter from traditional FIR/IIR filtering to polynomial interpolation with correction terms. This parameter change enables mode transitions by providing a flexible resampling approach that works effectively across different coding modes (LPD to FD and vice versa) without the constraints of fixed filter-based methods.
Data Source
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AI summary
The invention relates to a method of resampling an audio frequency signal in an audio frequency signal decoding, the resampling being carried out on a signal contained in a memory of a FIR type resampling filter by an interpolation method of higher order than one.The method is such that the interpolated samples are obtained by calculating a weighted average (802) of possible interpolation values calculated from coefficients of a plurality of interpolation polynomials of order higher than one (801), the coefficients being calculated over a plurality of intervals covering the time location of the sample to be interpolated, and that the interpolated samples complete a signal decoded according to a restricted predictive decoding mode (1006) in a transition frame between predictive decoding and transform decoding before a combination step (1008) between samples decoded according to restricted predictive decoding and completed and samples decoded according to transform coding (1003) in the transition frame. The invention also relates to a decoder implementing the method described.