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Super Monotonic Alignment Search (2409.07704v1)

Published 12 Sep 2024 in eess.AS and cs.AI

Abstract: Monotonic alignment search (MAS), introduced by Glow-TTS, is one of the most popular algorithm in TTS to estimate unknown alignments between text and speech. Since this algorithm needs to search for the most probable alignment with dynamic programming by caching all paths, the time complexity of the algorithm is $O(T \times S)$. The authors of Glow-TTS run this algorithm on CPU, and while they mentioned it is difficult to parallelize, we found that MAS can be parallelized in text-length dimension and CPU execution consumes an inordinate amount of time for inter-device copy. Therefore, we implemented a Triton kernel and PyTorch JIT script to accelerate MAS on GPU without inter-device copy. As a result, Super-MAS Triton kernel is up to 72 times faster in the extreme-length case. The code is available at \url{https://github.com/supertone-inc/super-monotonic-align}.

Summary

  • The paper presents a GPU-accelerated Super-MAS that drastically improves TTS alignment speed up to 72x compared to previous methods.
  • It restructures dynamic programming by eliminating nested loops and CPU-GPU copying, leveraging Triton kernels and PyTorch JIT for efficient parallelization.
  • These optimizations broaden TTS and speech recognition applications while challenging existing limits of monotonic alignment search algorithms.

Insights into Super Monotonic Alignment Search for Text-to-Speech

The paper entitled "Super Monotonic Alignment Search" investigates advancements in monotonic alignment search (MAS) within Text-to-Speech (TTS) applications. MAS, a pivotal algorithm initially introduced by the Glow-TTS model, has become a cornerstone in estimating alignments between text and speech without supervision. As MAS requires dynamic programming techniques to process possible alignments, its typical challenge lies in the computational complexity, which grows with the length of text and speech sequences. The original implementation, constrained by inefficiencies in parallel processing and high time costs due to CPU-GPU data exchanges, necessitated novel optimization.

Parallelization and Optimizations

Significant improvements are discussed in this paper through the development of a Super-MAS, which leverages Triton kernel and PyTorch JIT scripting for GPU acceleration. The parallelization problem is addressed by restructuring the algorithm to allow simultaneous processing across the text-length dimension. The authors successfully eliminate nested loops, a bottleneck in the conventional approach, significantly enhancing the method's ability to utilize GPU computation power efficiently.

Super-MAS stands out by achieving execution speed improvements, ranging from 19 times up to 72 times faster than the original Cython-implemented MAS in extreme-length scenarios. This dramatic improvement is attributed to the removal of inter-device copying and the deployment of inplace operations to manage memory usage effectively. Importantly, the algorithm's implementation in Triton and PyTorch ensures that the output quality remains consistent with its predecessors.

Practical and Theoretical Implications

From a practical standpoint, the alterations in the Super-MAS algorithm widen its application potential in various TTS systems and other speech recognition models where alignment precision is crucial. The significantly reduced computational time allows for enhanced real-time performance in applications requiring fast processing of large datasets.

Theoretically, these enhancements challenge previous assertions regarding the parallelization limits of MAS, suggesting a broader opportunity to reconsider and parallelize similar algorithms effectively in high-performance computing environments. The substratum provided by Triton and PyTorch JIT scripts facilitates these advancements, likely serving as a model for other computational frameworks in similar domains.

Future Directions

Looking ahead, this paper suggests ample room for further optimizations. While Super-MAS accelerates MAS without kernel fusing optimizations or simultaneous log-likelihood calculations, the incorporation of these and other techniques might extend the benefits achieved in this research to a wider array of scenarios. Further exploration into batch processing optimizations and finer-grained parallelization strategies could lead to further enhancement within the non-autoregressive TTS models.

Accessing Super-MAS's codebase through the open repository offers opportunities for collaborative improvements and empirical assessments across various hardware configurations, potentially pushing the boundaries of what's feasible in real-time speech processing workflows.

The paper exemplifies a focused effort to maximize efficiency in TTS through MAS and proposes a versatile framework that importantly contributes to the knowledge pool of alignment techniques in computational linguistics and machine learning applications.

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