Audio Envelope Reconstruction from Cumulative Sum Energy Bands
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Solution Overview
Problem
Current audio signal encoding methods, such as linear predictive coding (LPC) and scale-factor band approaches, face challenges in achieving a smooth and precise spectral envelope while maintaining low bit-rate encoding and reasonable computational complexity.
Innovation Solution
The proposed solution involves distributing quantization and coding of spectral envelopes, which splits the frequency band into equal energy blocks, allowing for efficient encoding and decoding of audio signals by determining aggregation functions and splitting points that divide the signal into portions with balanced energy values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If linear predictive coding (LPC) is used to model the spectral envelope, then the spectral representation is achieved, but the bit-rate increases and computational complexity rises
Solution Approach 1:
The frequency band is divided into multiple scale-factor bands, and within each band, the spectral envelope is represented by a small number of critical bands. This segmentation approach reduces the total number of parameters needed to represent the spectral envelope, thereby reducing bit-rate while maintaining spectral representation accuracy.
Solution Approach 2:
The patent transforms the spectral envelope representation from traditional LPC coefficients to a cumulative sum representation in the critical band domain. This parameter transformation allows for more efficient quantization and coding, reducing the bit-rate required to represent the same spectral information with comparable or improved precision.
2Manufacturing precision
If traditional quantization methods are used for spectral envelopes, then encoding is performed, but the envelope smoothness and spectral precision are insufficient
Solution Approach 1:
The patent applies a smoothing operation to the spectral envelope before quantization by modeling the cumulative sum of the smoothed envelope. This preliminary smoothing action ensures that the quantized representation maintains envelope smoothness while achieving precise spectral representation, avoiding the need for post-processing smoothing.
Solution Approach 2:
The patent introduces a cumulative sum representation as an intermediary domain between the original spectral envelope and the quantized code values. This intermediary representation naturally enforces smoothness constraints while preserving spectral precision, as the cumulative sum operation inherently smooths out high-frequency variations in the envelope.
3Measurement precision
If detailed spectral envelope representation is used, then spectral precision is improved, but computational complexity increases
Solution Approach 1:
The frequency spectrum is divided into a limited number of critical bands (e.g., 15-30 bands), and the spectral envelope is represented by the energy distribution across these bands. This segmentation reduces the computational complexity compared to representing every frequency point individually, while still providing adequate spectral precision for audio coding applications.
Solution Approach 2:
The patent transforms the spectral representation from a dense frequency-domain description to a sparse critical band energy distribution. This parameter reduction decreases computational complexity for both encoding and decoding operations while maintaining the essential spectral characteristics needed for high-quality audio reproduction.
Data Source
AI summary
An apparatus for generating an audio signal envelope from one or more coding values is provided. The apparatus includes an input interface for receiving the one or more coding values, and an envelope generator for generating the audio signal envelope depending on the one or more coding values. The envelope generator is configured to generate an aggregation function depending on the one or more coding values, wherein the aggregation function includes a plurality of aggregation points. Furthermore, the envelope generator is configured to generate the audio signal envelope such that the envelope value of each of the envelope points of the audio signal envelope depends on the aggregation value of at least one aggregation point of the aggregation function.