Dynamic Range Control Gain Curves for Fine Time-Resolution Audio
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Solution Overview
Problem
Current audio codecs, such as MPEG-AAC and ATSC, lack efficient Dynamic Range Control/Compression (DRC) mechanisms, leading to limited time resolution and aliasing distortions, particularly in applying DRC gains in the frequency domain before inverse MDCT filtering, which results in audible pre-echoes and insufficient support for multi-band DRC.
Innovation Solution
A system and method for encoding and applying DRC gain values in the time domain after audio signal reconstruction, using linear or spline interpolation to represent DRC gain curves with finer time resolution, allowing for faster gain updates and avoiding distortions by interpolating gain values between sparse samples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If DRC is applied in the frequency domain before inverse MDCT filtering, then DRC can be applied to compressed audio data, but aliasing distortions and pre-echoes occur due to limited time resolution
Solution Approach 1:
The patent inverts the conventional DRC application order by applying DRC in the time domain after inverse MDCT filtering rather than in the frequency domain before filtering. This reversal eliminates the aliasing and pre-echo artifacts caused by frequency-domain processing while maintaining the ability to process compressed audio data efficiently
Solution Approach 2:
The patent applies DRC gains to individual time-domain samples before the inverse MDCT filtering operation. By performing the gain application in advance at the sample level, the system achieves fine time resolution control without the artifacts that would result from coarser frequency-domain processing
2Productivity
If sparse DRC gain samples are used, then encoding efficiency is improved, but time resolution is insufficient leading to audible distortions
Solution Approach 1:
The patent creates multiple copies of sparse DRC gain samples at their original time positions, then performs linear interpolation between these copied samples to generate a dense sequence of gain values. This copying approach preserves the original sparse sample information while generating additional intermediate values for fine time resolution control
Solution Approach 2:
The patent uses linear interpolation as an intermediary process between sparse DRC gain samples. The interpolation algorithm acts as a mediator that generates intermediate gain values at unsampled time points, thereby achieving fine time resolution without requiring dense sampling in the first place
3Adaptability or versatility
If conventional DRC tools are used, then basic dynamic range control is achieved, but multi-band DRC support is insufficient
Solution Approach 1:
The patent segments the audio spectrum into multiple frequency bands and applies independent DRC processing to each band. By dividing the audio signal into separate frequency segments, the system achieves multi-band DRC capability that allows different compression characteristics for different frequency ranges, improving overall audio quality control
Data Source
AI summary
A system for encoding and applying Dynamic Range Control/Compression (DRC) gain values to a piece of sound program content is described. In particular, a set of DRC gain values representing a DRC gain curve for the piece of content may be divided into frames corresponding to frames of the piece of content. A set of fields may be included with an audio signal representing the piece of content. The additional fields may represent the DRC gain values using linear or spline interpolation. The additional fields may include 1) an initial gain value for each DRC frame, 2) a set of slope values at particular points in the DRC curve, 3) a set of time delta values for each consecutive pair of slope values, and/or 4) one or more gain delta values representing changes of DRC gain values in the DRC gain curve between points of the slope values.