Object-Based Audio Decoder Loudness Compensation During Rendering
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Solution Overview
Problem
Current audio rendering technologies in object-based audio coding systems fail to maintain consistent loudness across different audio programs or channels, leading to annoying volume fluctuations, despite normalization efforts like EBU Recommendation R128, due to the lack of effective decoder-side solutions for loudness estimation and compensation.
Innovation Solution
A decoder and encoder system that uses parametric loudness estimation based on object-level information to determine loudness compensation values, ensuring the output audio signal maintains a consistent loudness by adjusting audio object levels according to rendering information, without requiring explicit signal-based estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If audio rendering is conducted on the decoder side to allow flexible manipulation of audio objects, then adaptability and user control are improved, but the total loudness of the output signal varies significantly, causing annoying volume fluctuations between programs and channels
Solution Approach 1:
The encoder performs preliminary loudness estimation on the downmix signal and calculates compensation values before encoding. This pre-calculated loudness information is embedded in the bitstream, allowing the decoder to maintain consistent loudness without performing complex signal-based estimation, thus resolving the contradiction between rendering flexibility and loudness consistency
Solution Approach 2:
The system implements a feedback mechanism where loudness information from the encoder is fed back to the decoder through the bitstream. The decoder uses this feedback information to adjust its rendering process and maintain the intended loudness level, preventing volume fluctuations while preserving decoder-side adaptability
2Measurement precision
If signal-based loudness estimation is performed in the decoder to achieve accurate loudness measurement, then measurement precision is improved, but computational complexity and processing time increase significantly
Solution Approach 1:
Instead of performing complex signal-based loudness estimation in the decoder, the system copies pre-calculated loudness information from the encoder through the bitstream. This copying approach maintains measurement precision while dramatically reducing decoder computational complexity, as the decoder simply uses the provided loudness values rather than recalculating them
Solution Approach 2:
The encoder acts as an intermediary that performs the computationally intensive loudness estimation and passes the results to the decoder. This intermediary approach allows the decoder to achieve accurate loudness measurement without bearing the computational burden, effectively resolving the contradiction between precision and complexity
3Manufacturing precision
If normalization is applied at the encoder side according to EBU Recommendation R128, then loudness consistency between programs is improved, but decoder-side rendering operations still cause significant variations in output loudness
Solution Approach 1:
The encoder performs preliminary anti-action by pre-calculating loudness compensation values that counteract the expected loudness variations from decoder-side rendering. These compensation values are embedded in the bitstream, allowing the decoder to apply corrective adjustments that maintain consistent loudness despite rendering operations, thus resolving the contradiction between normalization and rendering impact
Data Source
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AI summary
A decoder for generating an audio output signal comprising one or more audio output channels is provided. The decoder comprises a receiving interface (110) for receiving an audio input signal comprising a plurality of audio object signals, for receiving loudness information on the audio object signals, and for receiving rendering information indicating whether one or more of the audio object signals shall be amplified or attenuated. Moreover, the decoder comprises a signal processor (120) for generating the one or more audio output channels of the audio output signal. The signal processor (120) is configured to determine a loudness compensation value depending on the loudness information and depending on the rendering information. Furthermore, the signal processor (120) is configured to generate the one or more audio output channels of the audio output signal from the audio input signal depending on the rendering information and depending on the loudness compensation value. Moreover, an encoder is provided.