Echo Attenuation in Digital Audio Decoders via False Alarm Zone Detection
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Solution Overview
Problem
Existing audio encoding methods, such as transform encoding, suffer from pre-echo and post-echo phenomena due to abrupt signal transitions, leading to noise distribution and degradation in audio quality, especially in musical sounds and speech sequences with plosive syllables, which current solutions like filtering and dynamic window switching either introduce additional complexity or fail to accurately attenuate echoes in synchronism with signal attacks.
Innovation Solution
A method and device for safe discrimination and attenuation of echoes in a multi-layer decoder, which identifies low-energy zones preceding high-energy transitions, defines a false-alarm zone, determines initial echo processing gain values, and inhibits echo attenuation in false-alarm zones to prevent unnecessary signal degradation, ensuring accurate echo reduction without affecting high-energy signals during attacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If transform encoding is used to achieve accurate frequency resolution, then manufacturing precision of frequency encoding is improved, but pre-echo and post-echo phenomena occur causing audio quality degradation
Solution Approach 1:
The patent applies preliminary action by detecting abrupt transitions in the encoded signal and proactively adjusting the window length before the echo problem fully manifests. When a transition is detected in one frame, the system switches to a shorter window length in subsequent frames to prevent pre-echo and post-echo degradation, thereby maintaining frequency resolution while avoiding echo artifacts.
2Object-generated harmful factors
If filtering is applied to reduce pre-echoes, then harmful echo factors are attenuated, but additional auxiliary parameters must be transmitted increasing device complexity
Solution Approach 1:
The patent applies dynamics by making the window length adaptive rather than fixed. The system dynamically switches between long windows (2048 samples) for stationary signals and short windows for transient signals with abrupt transitions. This dynamic adaptation allows pre-echo attenuation without requiring additional auxiliary parameters, as the window switching is controlled internally based on signal characteristics.
3Object-generated harmful factors
If dynamic window switching is used to reduce pre-echoes, then echo attenuation is improved, but additional delay is introduced reducing processing speed
Solution Approach 1:
The patent detects abrupt transitions in the encoded signal and proactively adjusts the window length before the echo problem fully manifests. When a transition is detected in one frame, the system switches to a shorter window length in subsequent frames, preparing in advance to minimize echo effects while reducing the delay compared to reactive approaches.
4Manufacturing precision
If long window length is used for accurate frequency resolution, then manufacturing precision is improved, but pre-echo phenomenon becomes more critical increasing harmful factors
Solution Approach 1:
The patent makes the window length dynamic, switching between long windows (2048 samples) for stationary signals where frequency resolution is critical and short windows for transient signals where pre-echo is problematic. This dynamic adaptation allows the system to optimize for frequency resolution when needed while minimizing pre-echo when transitions occur, without compromising overall audio quality.
Data Source
AI summary
The invention concerns a method for trained discrimination and attenuation of echoes of a digital audio signal generated from a transform coding, which consists, for each current frame of the signal. In comparing (A) in real time, in at least one frequency band a variable derived from one characteristic of the echo generating signal with that of a non-echo generating signal at a threshold value, and deducing therefrom (B) the existence or non-existence (C) of an echo derived from the transform coding, discriminating the existence of the echo and defining (D) a false alarm zone in the high-energy parts of the digital audio signal, determining an initial processing and attenuating the echoes (E) in the parts complementary to the low-energy false alarm zone and inhibiting (F) the attenuation of echoes in the false alarm zone. The invention is applicable to the technology of coders/decoders in particular hierarchical coders/decoders.