Audio Subband Encoding to Minimize MDCT Pre-Echo
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Solution Overview
Problem
Existing audio codec technologies fail to effectively control or eliminate pre-echo artifacts, particularly noticeable in audio with sharp impulses and transient signals, due to inaccuracies during time domain to frequency domain conversion and back, leading to suboptimal sound quality in dynamic and distributed IP-based multimedia systems.
Innovation Solution
A computer-implemented system and method that encodes sampled audio signals by identifying potential pre-echo events, generating an error signal, and encoding this information into a bitstream, allowing for the removal of pre-echo artifacts during decoding, using techniques such as pulse code modulation, adaptive pulse code modulation, and modified discrete cosine transform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If audio signals are encoded using traditional MDCT transformation, then compression efficiency is improved, but pre-echo artifacts are generated affecting sound quality
Solution Approach 1:
The audio signal is divided into multiple subbands using filter banks before MDCT transformation. Each subband is processed separately with appropriate block sizes, allowing transient signals to be handled with smaller blocks (reducing pre-echo) while maintaining compression efficiency for stationary signals through larger blocks in other subbands.
Solution Approach 2:
The system dynamically adjusts the block size for each subband based on the signal characteristics detected in that subband. Transient signals trigger smaller block sizes to minimize pre-echo, while stationary signals use larger blocks for better compression. This dynamic adaptation resolves the contradiction between compression efficiency and artifact reduction.
2Object-affected harmful factors
If smaller MDCT block sizes are used to reduce pre-echo, then pre-echo artifacts are minimized, but compression efficiency deteriorates
Solution Approach 1:
By segmenting the audio spectrum into multiple subbands, the system can apply different block sizes to different frequency regions. Only subbands containing transient signals use small blocks, while other subbands maintain large blocks for efficient compression, thus resolving the trade-off between pre-echo reduction and compression efficiency.
Solution Approach 2:
Different quality parameters (block sizes) are applied to different parts of the frequency spectrum based on local signal characteristics. Subbands with transient content receive small blocks for artifact reduction, while subbands with stationary content receive large blocks for compression efficiency, achieving optimal performance in each local region.
3Stability of the object's composition
If fixed bit rates are used for audio encoding, then transmission stability is improved, but adaptability to dynamic network conditions deteriorates
Solution Approach 1:
The encoder dynamically adjusts encoding parameters including bit rate allocation across subbands based on signal characteristics and network conditions. This allows the system to maintain stable transmission by adapting to varying network capacity while preserving audio quality through intelligent resource allocation, resolving the contradiction between stability and adaptability.
Data Source
AI summary
An encoder operable to filter audio signals into a plurality of frequency band components, generate quantized digital components for each band, identify a potential for pre-echo events within the generated quantized digital components, generate an approximate signal by decoding the quantized digital components using inverse pulse code modulation, generate an error signal by comparing the approximate signal with the sampled audio signal, and process the error signal and quantized digital components. The encoder operable to process the error signal by processing delayed audio signals and Q band values, determining the potential for pre-echo events from the Q band values, and determining scale factors and MDCT block sizes for the potential for pre-echo events.