Show default confidence in ASR node

[alexanderkoller]

By default, the confidence textfield in the ASR node properties is blank. This makes it hard for a user to guess what kind of value they should enter here. Can we initialize the contents of the textfield with the default confidence value?

[timobaumann]

I found the following in the source: (0 map anything to grammar, 100 reject if it's not a perfect match) and:

        thresholds must be converted to be useful in Sphinx.
        TIMO tested this with a bunch of files containing digits
        except for one or two and tested a grammar that only allowed
        those two digits. The range of false positives varied within
        a range of 10e-25 and 10e-50 (anything accepted as one|two at 10e-50).

        thus 0 -> 10e-50
        and  1 -> 10e-25

If no value is set, the default is 0 (i.e., also accept low confidence values)

[timobaumann]

there are two possibilities in the speech recognition: (a) follow the paths in the grammar, (b) follow an out-of-grammar path. The probability of (b) is set with the confidence threshold.

I.e., if you set a high threshold, it's likely that the speech recognizer follows (b) and the result is that you get out-of-grammar except if what you speak sounds very much like what the grammar expected. Equivalently, if you set a low threshold, the speech recognizer is very unlikely to follow (b) and anything you say will sound like one of the possibilities in the grammar.

[timobaumann]

I don't know where this documentation should go, so I'm leaving it here for the moment.