Subject: [speechsc] Hotword Recognition and Timers

From: Andrew Wahbe <[email-masked]>
Date: Thu, 13 Apr 2006 17:23:16 -0400

The description of how timers (no-input and recognition) are used during 
hotword recognition is inconsistent. In sections 9.4.7, it is stated 
that "For a hotword recognition mode, this timer is started when the 
user begins speaking. Note that for Hotword mode recognition the 
START-OF-INPUT event is not generated." However, section 9.9 states that 
for the hotword case: "The Recognition-Timer gets started at the 
beginning of RECOGNIZE."

It seems that section 9.9 is incorrect (or at least is inconsistent with 
VoiceXML).

Section 9.9 omits any mention of the no-input timer for the hotword mode 
recognition case; however, none of the sections that deal with the 
no-input timer make a distinction between the hotword and non-hotword 
cases. VoiceXML also does not make this distinction. It would seem that 
section 9.9 should be changed to indicate that no-input timers are 
started in the hotword case and that no-input-timeout is a valid 
completion cause for a hotword recognition.

A related question worth considering is if the recognition timer is 
reset at any point, for example, on the detection of silence. Consider 
the case when maxspeech has a value of say 20 seconds (a 
typical/reasonable value) and hotword barge-in is being used on a prompt 
that is 30 seconds long. This would mean that a user that spoke briefly 
2 seconds into the prompt (and was silent for the remainder of the 
prompt) would experience a maxspeech timeout at about 22 seconds into 
the prompt. They would not hear the whole prompt which seems 
inappropriate. The reason for maxspeech timeout is to catch continuous 
noise and keep it from occupying a recognizer; but what should happen in 
periods of silence in the hotword case?

Similarly, when is the no-input timer canceled in the hotword case? Is 
it when speech (not necessarily matching) is detected? Or is it only 
upon a match?

The correct behavior in my opinion is that the no-input timer is 
canceled only on a match, and that the recognition timer should be reset 
if silence (determined by complete timeout and incomplete timeout) is 
detected. If we are just processing intermittent noise, the no-input 
timer will eventually expire. Continuous noise is handled by the 
recognition timer. Of course other there are other possibilities as 
well, this is just one option that I think fits with VoiceXML.
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