MPEG Surround Decoder Delay Alignment for Downmix Synchronization
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Solution Overview
Problem
The synchronization of multi-channel audio signals between an MPEG surround decoder and a HE-AAC decoder is disrupted due to different delays between downmix signals in the time domain and the Quadrature Mirror Filter (QMF) domain, causing desynchronization of spatial parameters.
Innovation Solution
A delay unit is introduced to account for the delays in the QMF and Nyquist filter banks, ensuring synchronization by adjusting the timing of downmix signals from the HE-AAC decoder to the MPEG surround decoder, whether in the real or complex QMF domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If downmix signals are converted to frequency bands using a hybrid filter bank (QMF bank and Nyquist filter bank), then multi-channel audio signals can be restored from compressed downmix signals, but a delay occurs in the signal processing
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the delay values (704 samples for QMF analysis, 257 samples for QMF synthesis, and 0 samples for Nyquist banks) before actual decoding. The delay compensation is prepared in advance by determining the total delay (961 samples) and implementing it through buffer management and timing synchronization mechanisms before the audio signals are fully processed, thereby reducing the perceived delay impact on the restored audio quality
2Manufacturing precision
If QMF processing is performed on downmix signals in the high-quality MPEG surround decoder, then audio quality is improved, but a delay of 704 samples occurs in the QMF analysis filter bank and 257 samples in the QMF synthesis filter bank
Solution Approach 1:
The patent applies parameter changes by modifying the timing parameters of the QMF filter bank operations. It changes the delay parameter from 0 to 704 samples in the QMF analysis filter bank and from 0 to 257 samples in the QMF synthesis filter bank. These parameter adjustments are coordinated with buffer management strategies that shift data timing to compensate for the introduced delays, thereby maintaining audio quality while managing the timing impact
3Adaptability or versatility
If spatial parameters are extracted from MPEG surround side information signals, then multi-channel audio restoration is enabled, but the spatial parameters are delayed by 961 samples relative to downmix signals
Solution Approach 1:
The patent applies feedback by implementing a delay compensation mechanism that monitors the timing relationship between spatial parameters and downmix signals. The system measures the 961 sample delay and feeds this information back to adjust the processing timing of spatial parameters. This feedback loop ensures that spatial parameters are aligned with downmix signals in the time domain, maintaining synchronization while preserving the multi-channel audio restoration capability
Data Source
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AI summary
Provided is a method for controlling synchronizing downmix signals and MPEG surround side information signals by controlling a delay according to the kind of downmix audio signals in an MPEG surround decoder. When multi-channel audio signals are restored using an HE-AAC decoder and a low-power MPEG surround decoder and complex QMF signals outputted from the HE-AAC decoder are used as downmix signals, a delay unit compensates for a delay caused in a real-to-complex converter. Anther delay unit delays spatial parameters to compensate for a delay caused in QMF and Nyquist banks when time-domain downmix signals are used. Also, when multi-channel audio signals are restored using an HE-AAC decoder and a high-quality MPEG surround decoder and complex QMF signals outputted from the HE-AAC decoder are used as downmix signals, a delay unit compensates for a delay caused in a real-to-complex converter.