Two-stage speaker adaptation in subspace Gaussian mixture models
Bibliographic record
Abstract
A two-stage speaker adaptation approach is proposed for the subspace Gaussian mixture model (SGMM) [1] in large vocabulary automatic speech recognition (ASR). The SGMM differs from the more well known continuous density hidden Markov model (CDHMM) in that a large portion of the SGMM parameters are dedicated to shared full covariance Gaussian subspace parameters and a relatively small number of parameters are used for state dependent projection vectors. Both model space and feature space adaptation are investigated. First, an efficient regression based approach for subspace vector adaptation (SVA) is presented. Second, an efficient approach is presented for feature space adaptation using constrained maximum likelihood linear regression (CMLLR) in the SGMM. While both of these adaptation scenarios have previously been investigated in the context of the SGMM [2, 3], a more efficient and numerically stable procedure is presented here for estimating the parameters of the regression based transformations. Both transformation matrices are obtained using an optimization technique that iteratively updates the rows of the regression matrices. It is shown that using these feature space and model space approaches for unsupervised speaker adaptation provides complementary improvements in SGMM based ASR word accuracy.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.002 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".