Automatic Gain Compensation Correction via Inaudible Pilot Tones
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Solution Overview
Problem
Existing audio recording systems, particularly in mobile devices, often apply automatic gain compensation (AGC) system-wide without user control or visibility, which can distort the dynamic range of recordings, especially in music recordings where precise signal management is crucial.
Innovation Solution
A method and device that emit inaudible reference audio signals to infer and undo AGC effects by analyzing variations in these signals, allowing for the restoration of original dynamic ranges in recorded audio content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If automatic gain compensation is applied system-wide to all audio recordings, then weak signals are enhanced and strong signals are reduced, but the original dynamic range of music recordings is distorted and control over AGC gains is lost
Solution Approach 1:
The patent introduces an ultrasonic pilot tone as an intermediary signal that carries information about the AGC gain applied to the audio signal. This pilot tone is modulated with the AGC gain values and transmitted along with the audio content, allowing receiving devices to retrieve and use this information to reverse the AGC effects without requiring direct control over the AGC processing itself
Solution Approach 2:
The system implements a feedback mechanism where the AGC gain values are extracted from the received audio signal by analyzing the ultrasonic pilot tone, and this extracted gain information is then used to apply compensating gain adjustments to restore the original dynamic range of the recorded audio
2Extent of automation
If system-level AGC is enabled in mobile devices, then audio signal levels are automatically adjusted, but applications lack interface to adjust or read AGC gains
Solution Approach 1:
The ultrasonic pilot tone serves as a mediator that bridges the gap between the system-level AGC processing and application-level control needs. By embedding AGC gain information in the pilot tone, the system enables applications to read and interpret AGC parameters without requiring direct access to or control over the system-level AGC processing mechanisms
Solution Approach 2:
The ultrasonic pilot tone performs multiple functions: it carries the AGC gain information, remains inaudible to humans, and can be processed by any application that implements the appropriate detection and analysis algorithms, thereby providing universal access to AGC control capabilities across different applications
3Reliability
If AGC is applied to music recordings, then signal levels are flattened, but music-specific dynamics processing cannot be effectively applied
Solution Approach 1:
The system performs preliminary action by embedding the AGC gain information in the ultrasonic pilot tone during the recording process itself. This allows receiving devices to have the necessary information in advance to reverse the AGC effects and restore the original dynamic range before applying music-specific processing
Solution Approach 2:
The system applies preliminary anti-action by providing the means to counteract the AGC effect immediately upon receiving the audio signal. By extracting the gain information from the pilot tone and applying compensating gain adjustments, the system undoes the dynamic range compression caused by AGC, restoring the original signal characteristics for subsequent music-specific processing
Data Source
AI summary
Methods, systems, and computer program products that infer and correct automatic gain compensation (AGC) values over time are described. A device emits a series of inaudible reference audio signals during recording. The reference audio signals have a constant amplitude. A microphone of the device records the reference audio signals while recording audio content. The device may apply AGC during the recording. An AGC inference module receives the recorded signals and extracts a representation of the reference audio signals, which have been subject to the AGC. The AGC inference module determines variations in levels of the extracted representation of the reference audio signals over time. Based on the variations, the AGC inference module infers the AGC applied to the recording over time. The AGC inference module can then provide the AGC for reading, or undo effects of the AGC applied to the audio content.