Decoder-Side Loudness Adjustment for Live Audio DRC
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Solution Overview
Problem
In metadata-based dynamic range control (DRC) for online applications like live audio streaming, the challenge arises when the program loudness of the sound program is unknown, leading to improper adjustment of the compressor characteristic and potential audible pumping artifacts.
Innovation Solution
The solution involves deferring loudness adjustment (loudness normalization) from the encoder side to the decoder side and allowing the compressor characteristic to be changed in the decoder side during metadata-based DRC gain sequence processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If loudness normalization is performed at the encoder side using predicted program loudness, then the compressor characteristic can be adjusted in advance, but the adjustment may be improper when actual program loudness deviates significantly from predicted values
Solution Approach 1:
The encoder performs preliminary loudness normalization using predicted program loudness values before the actual program loudness is known. This allows the compressor characteristic to be adjusted in advance, improving processing efficiency while accepting that the adjustment may need refinement later if actual loudness deviates from predictions.
Solution Approach 2:
The system implements feedback by monitoring actual program loudness during streaming and comparing it with predicted values. When significant deviations are detected, the decoder adjusts the compressor characteristic in real-time to compensate for improper initial adjustment, ensuring accurate loudness control throughout the program.
2Manufacturing precision
If metadata-based DRC gain sequence is applied at the decoder side, then quality improves due to larger look-ahead time interval, but the compressor characteristic cannot be properly adjusted when program loudness is unknown
Solution Approach 1:
The system transitions from static compressor characteristics (determined at encoding) to dynamic characteristics that can be adjusted during playback. The decoder modifies the compressor characteristic in real-time based on actual program loudness measurements, enabling both high precision DRC gain application and adaptability to unknown loudness levels.
3Reliability
If real-time loudness normalization is attempted during live streaming, then proper loudness control can be achieved, but audible pumping artifacts may occur due to time-varying gain adjustments
Solution Approach 1:
The system applies partial loudness normalization at the encoder using predicted loudness, then completes the normalization at the decoder using actual loudness measurements. This division of labor reduces the rate of gain changes compared to full real-time normalization, minimizing pumping artifacts while maintaining loudness control accuracy through the combined approach.
Data Source
AI summary
A bitstream is obtained by a decoder side, that contains an encoded version of an audio signal and an instantaneous loudness sequence of the audio signal. The instantaneous loudness sequence has not been loudness normalized. A dynamic range control, DRC, gain sequence is produced by applying the instantaneous loudness sequence to a DRC characteristic, with loudness normalization. The DRC gain sequence is applied to the decoded audio signal. Other aspects are also described and claimed.