[asterisk-speech-rec] How to enable N-Best decoding? CRM:00171167

[Stephen Keller]

> Also, I've been finding that a lot of times the Speech engine 
> takes a long time (on the order of 1 or a several seconds) to 
> recognize speech. 

There are a few things that affect the length of time before you'll get
results:

1. The end of speech delay is probably the most common. This is the
amount of time that we have to detect silence before the Speech Engine
begins doing a decode. If this is too low, it causes problems as callers
get off before they've really finished speaking (it's especially
important to set this high for utterances where you expect a lot of
pauses between words, such as when collecting large strings of digits).
You can adjust this by changing the vad_eos_delay in your lumenvox.conf
file; by default it's set to 2000 ms. For really short yes/no types of
prompts, you can set this value pretty low (800ms or less).

2. Extra background noise that the Engine is mistaking for speech could
also falsely cause it to not begin doing a decode, though this is a
pretty rare thing.

3. The Engine may also be taking a while to perform the actual decode.
Speech recognition is a pretty resource intensive process, and so
overworked hardware can sometimes cause this. The amount of time to
decode goes up as the length of the utterance and size of the grammars
go up as well (increasing the grammar size increases the Engine's search
space). If you use our Speech Tuner, you can see how long a decode
actually took by loading up some response files and browsing
interactions with the Call Browser, and clicking the "View Details"
button for a given decode. One of the details will be the decode time.

So I would recommend first seeing how long decodes are taking and then
try changing vad_eos_delay. Let us know how it goes.

Stephen Keller
LumenVox Support
P: 877-977-0707, just say "Support"
F: 858-707-7072
Support at LumenVox.com
www.LumenVox.com

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