[asterisk-speech-rec] DTMF response time improved during speech recog. instances

[John Todd]

I ran into a problem a few days ago with speech recognition in 
generic conversion of DTMF-based applications.  We have several apps 
here which rely upon single keypresses in order to take some action, 
like most IVR apps.  The problem was that the existing method by 
which Asterisk was handing off DTMF was a bit on the sluggish side 
for entries made on the DTMF keypad - there was around a 5 second 
delay between a keypress and an action being returned to the 
dialplan.  This was a drastic performance cut from our existing apps, 
so voice-enabling them wasn't possible until that bug was fixed.

I'm pleased to say a quick response by Lumenvox (StephenKeller) and 
Digium (file) added an as-yet undocumented repair variable to solve 
the problem.  It was repaired and added to 1.4 on June 15th 2007, and 
patches cleanly to other versions (it's only about 5 lines in 
app_speech_utils.c)

You can now set a variable called "SPEECH_DTMF_MAXLEN" from within 
the dialplan which indicates the maximum number if DTMF digits your 
grammar is expecting.   In our case, where menus were all 
single-keypress to start with, we set the value to "1" and it returns 
back the values immediately.  I also created .gram files for 
single-digit keypresses for both voice and DTMF, though I'm uncertain 
if this is required now with this patch.  Interestingly, if you 
specify "2" as the length of digits, but your DTMF grammar only 
indicates a single digit, the grammar is ignored and the number of 
digits you enter with DTMF is returned.  If you speak more than two 
digits, the system acts properly according to the grammar and only 
the first digit is returned.  I've been told this is because Asterisk 
is handling the DTMF (and is being instructed what to do with 
SPEECH_DTMF_MAXLEN) and the voice recognition portion is using the 
grammar.

Note: I've not been able to get "#" and "*" to work yet with the DTMF 
signalling, but I've been talking with Lumenvox about if this is a 
syntax problem with my attempts, or a deeper bug.


Examples below.

JT




[root at blah grammars]# more digit.gram
#ABNF 1.0 UTF-8;

language en-US;

mode voice;

tag-format <lumenvox/1.0>;

$Digit = (ONE:"1"        |
           TWO:"2"        |
           THREE:"3"      |
           FOUR:"4"       |
           FIVE:"5"       |
           SIX:"6"        |
           SEVEN:"7"      |
           EIGHT:"8"      |
           NINE:"9"       |
           (ZERO | O):"0" );
[root at blah grammars]#



[root at blah grammars]# more digit-dtmf.gram
#ABNF 1.0 UTF-8;

language en-US;

mode dtmf;

tag-format <lumenvox/1.0>;

root $Digit;

$Digit = (1:"1"      |
           2:"2"      |
           3:"3"      |
           4:"4"      |
           5:"5"      |
           6:"6"      |
           7:"7"      |
           8:"8"      |
           9:"9"      |
           0:"0");

[root at blah grammars]#

[test]
exten => s,1,SpeechCreate
exten => s,n,Set(THRESHOLD=500)
exten => s,n,Set(SPEECH_DTMF_MAXLEN=1)
exten => s,n,SpeechActivateGrammar(digit)
exten => s,n,SpeechActivateGrammar(digit-dtmf)
exten => s,n,SpeechStart
exten => s,n,SpeechBackground(tt-monkeys)
exten => s,n,NoOp(The value in SPEECH_TEXT is ${SPEECH_TEXT(0)})
exten => s,n,SayDigits(${SPEECH_TEXT(0)})

exten => s,n,Hangup

exten => i,1,Playback(tt-somethingwrong)
exten => i,n,Hangup