Audio Decoding Circuit for Adaptive High-Frequency Reconstruction
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Solution Overview
Problem
Existing frequency band expanding techniques, such as those described in PTL 1, struggle with accurately reproducing the high-frequency spectrum due to a fixed, predetermined frequency envelopment, leading to a loss of sound clarity and precision in music playback.
Innovation Solution
A frequency band expanding device that utilizes a low-pass filter, delay circuit, band pass filters, feature amount calculating circuit, high-frequency subband power estimating circuit, and high-frequency signal generating circuit to dynamically estimate and generate high-frequency components based on low-frequency signals, using adjustable coefficients and feature amounts to match the original power spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed predetermined frequency envelopment is used to generate high-frequency components, then the device complexity is reduced, but the manufacturing precision of the frequency band expansion deteriorates
Solution Approach 1:
The patent applies dynamics by making the frequency envelopment adjustable rather than fixed. The high-frequency subband power estimating circuit dynamically adjusts the frequency envelopment coefficients based on the characteristics of the input signal, allowing the system to adapt to different music types and playback environments. This resolves the contradiction by enabling precise high-frequency reproduction without requiring excessive device complexity, as the adjustment is achieved through software/control parameters rather than hardware reconfiguration.
Solution Approach 2:
The patent changes the parameter of frequency envelopment from a fixed predetermined value to an adjustable parameter. By allowing the frequency envelopment coefficients to be modified based on signal characteristics and user preferences, the system achieves higher manufacturing precision in frequency band expansion while maintaining reasonable device complexity through parameter optimization rather than structural complexity.
2Reliability
If the frequency envelopment is adjusted to match original power spectrum, then the sound quality is improved, but the ease of operation deteriorates
Solution Approach 1:
The patent applies self-service by enabling the frequency band expanding device to automatically adjust its own frequency envelopment parameters based on the input signal characteristics. The high-frequency subband power estimating circuit autonomously analyzes the low-frequency signal and generates appropriate high-frequency components without requiring manual intervention. This resolves the contradiction by maintaining high sound quality through automatic adaptation while preserving ease of operation, as the system configures itself without user input.
Solution Approach 2:
The patent implements feedback mechanisms where the estimated high-frequency subband power is continuously adjusted based on the relationship between low-frequency and high-frequency components. This closed-loop approach ensures high sound quality by constantly optimizing the frequency envelopment to match the original power spectrum characteristics, while the automation of this feedback process maintains operational simplicity.
3Loss of substance
If high-frequency components are generated from low-frequency signals, then the loss of substance is reduced, but the measurement precision of high-frequency power spectrum deteriorates
Solution Approach 1:
The patent introduces an intermediary approach by using the low-frequency signal as a basis to estimate high-frequency characteristics through the high-frequency subband power estimating circuit. Rather than directly measuring high-frequency components that are not present in the encoded signal, the system uses mathematical models and statistical relationships to infer high-frequency power spectrum characteristics. This resolves the contradiction by reducing loss of high-frequency components through intelligent estimation while maintaining measurement precision through sophisticated signal processing techniques.
Solution Approach 2:
The patent applies preliminary action by pre-calculating and storing frequency envelopment coefficients and statistical characteristics during the encoding phase or initial setup. These pre-computed parameters are then used during decoding to rapidly generate accurate high-frequency components without requiring complex real-time measurements. This resolves the contradiction by reducing the need for precise real-time high-frequency measurement while minimizing loss of high-frequency information through advance preparation of estimation data.
Data Source
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AI summary
The present invention relates to a decoding device comprising: a demultiplexing circuit configured to demultiplex input encoded data into low-frequency encoded data, coefficient information for obtaining a coefficient set, and smoothing information relating to smoothing; a low-frequency decoding circuit configured to decode the low-frequency encoded data to generate a low-frequency signal; a subband dividing circuit configured to divide the low-frequency signal into a plurality of subbands to generate a low-frequency subband signal for each of the subbands; a feature amount calculating circuit configured to calculate a feature amount based on the low-frequency subband signals; a smoothing circuit configured to subject the feature amount to smoothing based on the smoothing information indicating the number of frames used for the smoothing; a generating circuit configured to generate a high-frequency signal based on the coefficient set obtained from the coefficient information, the feature amount subjected to smoothing, and the low-frequency subband signals; and a synthesizing circuit configured to synthesize an output signal based on the low-frequency signal and the high-frequency signal and outputting the output signal.