Audio Downmix Envelope Coding for Low-Bitrate Energy Accuracy
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Solution Overview
Problem
Low bitrate audio encoding of downmixed signals leads to imprecise encoding of envelope energy information, resulting in degraded audio quality, particularly at higher frequencies.
Innovation Solution
Encoding envelope energy information redundantly in the bitstream, allowing decoders to apply correction gains for accurate energy level representation, especially at low bitrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If audio signals are encoded at low bitrate by generating downmix signals, then bandwidth is minimized, but audio quality degrades due to imprecise encoding of envelope energy information
Solution Approach 1:
The audio signal is divided into multiple frequency bands, and envelope energy information is separately encoded for each band. This segmentation allows precise encoding of energy characteristics in different frequency ranges independently, maintaining audio quality while using low bitrate downmix signals.
Solution Approach 2:
Envelope energy information is calculated and encoded in advance during the encoding phase, before transmission. The decoder then uses this pre-encoded energy information to adjust and correct the downmix signal, ensuring accurate energy representation without requiring high bitrate transmission.
2Productivity
If downmix signals are used to reduce channel count, then bitrate efficiency improves, but energy information accuracy deteriorates
Solution Approach 1:
Envelope energy information acts as an intermediary parameter that bridges the downmix signal and the original audio quality. The decoder uses this energy information to adjust the downmix signal, effectively mediating between the compressed downmix and the desired high-quality output.
Solution Approach 2:
The encoding system changes parameters by separately encoding envelope energy information for each frequency band alongside the downmix signal. This parameter change allows the decoder to adjust energy levels dynamically, maintaining accuracy despite using efficient downmix encoding.
3Loss of information
If envelope energy information is encoded in downmix signals, then some energy information is preserved, but precision is lost due to low bitrate constraints
Solution Approach 1:
The frequency spectrum is segmented into multiple bands, with dedicated envelope energy encoding for each band. This segmentation prevents energy information loss by ensuring that energy characteristics of different frequency ranges are independently preserved with sufficient precision.
Solution Approach 2:
Envelope energy information is pre-calculated and encoded with high precision during the encoding phase, then transmitted efficiently. The decoder applies this pre-encoded information to restore precise energy levels, overcoming the limitations of low bitrate transmission.
Data Source
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AI summary
A method for encoding envelope information is provided. In some implementations, the method involves determining a first downmixed signal associated with a downmixed channel associated with an audio signal to be encoded. In some implementations, the method involves determining energy levels of the first downmixed signal for a plurality of frequency bands. In some implementations, the method involves determining whether to encode information indicative of the energy levels in a bitstream. In some implementations, the method involves encoding the determined energy levels. In some implementations, the method involves generating an energy control value indicating that energy levels are encoded. In some implementations, the method involves generating the bitstream, wherein the energy control value and the information indicative of the energy levels are usable by the decoder to adjust energy levels associated with the first downmixed signal.