Audio Decoding with Smoothed High-Frequency Band Expansion
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Solution Overview
Problem
Existing frequency band expanding techniques, such as those described in PTL 1, fail to accurately reproduce the high-frequency spectrum due to a fixed, predetermined frequency envelopment, leading to a loss of sound clarity in music playback.
Innovation Solution
A frequency band expanding device that includes a low-pass filter, delay circuit, band pass filters, feature amount calculating circuit, high-frequency subband power estimating circuit, high-frequency signal generating circuit, and signal adder, which dynamically estimates high-frequency subband power based on input signal features to generate high-frequency components, enhancing precision and sound quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed predetermined frequency envelopment is used for band expansion, then the encoding process is simple, but the high-frequency spectrum cannot be accurately reproduced leading to loss of sound clarity
Solution Approach 1:
The patent applies dynamics by replacing the fixed predetermined frequency envelopment with a dynamic estimation process. The high-frequency subband power is estimated based on the actual input signal characteristics through filtering and power calculation operations, allowing the frequency envelopment to adapt to different input signals rather than remaining static. This resolves the contradiction by making the encoding process flexible enough to accurately reproduce high-frequency spectra while maintaining reasonable complexity through systematic signal processing.
Solution Approach 2:
The patent changes the parameter of frequency envelopment from a fixed predetermined value to a dynamically calculated value based on input signal parameters. By calculating high-frequency subband power through filtering operations and power calculations on the input signal, the system adapts the frequency envelopment parameters to match the actual signal characteristics. This parameter change enables accurate high-frequency reproduction without requiring overly complex encoding processes.
2Reliability
If high-frequency signal components are generated from low-frequency signal components using dynamic estimation, then sound quality is improved, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the frequency spectrum into multiple subbands using band-pass filters. The low-frequency signal components are processed through a series of filters with different cutoff frequencies to extract specific frequency ranges. This segmentation allows the system to handle different frequency components separately and reconstruct them with accurate high-frequency characteristics, improving sound quality while managing device complexity through modular frequency processing.
Solution Approach 2:
The patent introduces intermediary processing steps between the low-frequency input signal and the final high-frequency output. Intermediate frequency components are extracted through band-pass filtering, and high-frequency subband power is estimated as an intermediary representation before generating the final high-frequency signal components. These intermediary representations serve as bridges that enable accurate sound quality reproduction without requiring direct complex transformation from low to high frequencies.
3Measurement precision
If high-frequency subband power is estimated from low-frequency signal components, then the frequency band is expanded accurately, but the processing time increases
Solution Approach 1:
The patent applies preliminary action by pre-defining the filtering structure and frequency envelopment calculation methodology before actual signal processing. The band-pass filters are configured with predetermined cutoff frequencies, and the high-frequency subband power estimation process is established in advance based on the input signal characteristics. This preliminary setup enables accurate frequency band expansion while reducing processing time during actual operation, as the systematic framework is already in place rather than being constructed in real-time.
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.