End-to-End Automatic Speech RecognitionIntegrated With CTC-Based Voice Activity Detection
Table 2: Effect of value of offset margin.
['[ITALIC] ms', 'eval1 [%]', 'eval2 [%]', 'eval3 [%]', 'Avg. [%]']
The initial experiment only used the CTC decoding instead of the joint CTC/attention decoding. It was varied from 0 to 3 while minimum blank duration threshold V=16 and offset margin me=2. It can be said from the table that the onset margin is important to achieve correct recognition results. The value of me was also varied from 0 to 3 while V=16 and ms=2. The performance difference between with and without the offset margin, me>0 and me=0, was significantly large. These two margins seem to buffer the time-lag of the CTC softmax output. To investigate the sensitivity to the change of the minimum blank duration threshold, the value of V was varied with the fixed onset and offset margins (ms=2 and me=2). From the table, a low CER can be obtained by selecting a large threshold value, as expected. However, reasonable recognition performance could be achieved by a medium threshold value, e.g., V=16. This means that 640 (=16×4×10) ms was used as a threshold value. The duration seems to be reasonable for detecting short pause, indicating that the proposed method can intuitively tune VAD parameters in contrast to the conventional VAD methods requiring non-intuitive parameters such as an energy threshold.