Audio Encoder Block Switching for Pre-Echo Control
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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 transformations 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
1Productivity
If MDCT transform is used to convert time domain signal to frequency domain and back, then audio encoding efficiency is improved, but pre-echo artifacts are generated due to error spreading across block size
Solution Approach 1:
The audio signal is divided into multiple blocks for MDCT processing, and the patent identifies specific blocks containing transient signals. By segmenting the processing approach - using different block sizes (fine block sizes for transient regions, coarse block sizes for stationary regions) - the patent prevents error spreading across entire large blocks, thereby reducing pre-echo artifacts while maintaining encoding efficiency.
Solution Approach 2:
The patent dynamically adjusts MDCT block sizes based on the characteristics of the audio signal. When transient signals are detected, smaller block sizes are used to limit the temporal spread of quantization errors. This dynamic adaptation allows the system to maintain high encoding efficiency for stationary signals while minimizing pre-echo artifacts during transient regions.
2Quantity of substance
If quantization is applied during MDCT transformation, then bit rate is reduced, but pre-echo artifacts become noticeable especially in transient signals
Solution Approach 1:
The patent applies different quantization strategies to different regions of the audio signal. In regions containing transient signals, finer quantization is applied to reduce pre-echo artifacts, while in stationary regions, coarser quantization is used to maintain lower bit rates. This local differentiation allows the system to achieve acceptable quality for transient signals without significantly increasing the overall bit rate.
Solution Approach 2:
The patent changes the quantization parameters (block size, quantization step size) based on the detected signal characteristics. For transient regions, smaller block sizes and adjusted quantization parameters are used to minimize pre-echo, accepting a local increase in bit rate. For stationary regions, larger block sizes and coarser quantization are used to maintain low bit rate, achieving an overall efficient bit rate while reducing pre-echo artifacts.
3Device complexity
If fixed block size MDCT is used for encoding, then encoding complexity is reduced, but pre-echo cannot be effectively controlled in dynamic audio signals
Solution Approach 1:
The patent transitions from fixed block size to dynamic block size selection. The encoder detects transient signals and adjusts the MDCT block size accordingly - using small blocks for transient regions and large blocks for stationary regions. This dynamic approach effectively controls pre-echo artifacts while the complexity increase is managed through efficient detection algorithms and block size switching mechanisms.
Solution Approach 2:
The patent performs preliminary analysis of the audio signal to detect transient regions before applying MDCT transformation. By identifying transient signals in advance, the encoder can pre-select appropriate small block sizes for these regions, preventing pre-echo artifacts from the outset. This preliminary action adds some complexity but avoids the need for more complex post-processing to remove pre-echo.
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. The encoder operable to transform the error signal into high resolution frequency components using the MDCT block sizes, quantize the scale factors and frequency components, and encode the quantized lines, block sizes, and quantized scale factors for inclusion in the bitstream.