Unsupervised adaptation without estimated transriptions

To estimate the unknown distortion parameters from input test signals, estimated transcriptions are typically used for unsupervised adaptation. In a low signal to noise ratio (SNR) condition, the transcription estimated by a decoding procedure can be error prone because of the high mismatch between the acoustic models and the input signal. As a result, it can cause performance degradation of the adapted systems. To account for this problem, we propose an unsupervised adaptation method that can adapt the acoustic models without the estimated transcription. Instead, Gaussian mixture models (GMM) and pseudo phoneme models (PPM) are used. Using these models the unknown distortion parameters are estimated based on the vector Taylor series (VTS) model adaptation scheme. On the Aurora2 task, we obtained relative reduction of 5.4% in word error rate (WER).