This chapter addresses robust front-end processing for automatic speech recognition in
noisy environments. To recognize corrupted speech accurately, it is necessary to employ robust
methods against various types of interference. Usually, noise suppression is used for the frontend
processing of speech recognition in the presence of noise. Voice activity detection (VAD)
is also used for front-end processing to eliminate the redundant non-speech period. VAD and
noise suppression are typically combined as series processing. VAD and noise suppression should
not be assumed to be separate techniques, because the output information of these methods is
mutually beneficial. Thus, this chapter introduces the integrated front-end processing of VAD and
noise suppression, which can utilize each others' input-output information.
