This document discusses best practices for tuning speech-enabled interactive voice response (IVR) systems. It recommends tuning prompts to use natural language and specify options clearly. Grammars should cover all expected user responses while avoiding unnecessary phrases. Parameter optimization is also important, especially setting the rejection threshold and endpointer sensitivity. The goal is to make the IVR communication natural and intuitive for users.

1. State of the Art/Best Practices in
Speech Technology
Dan Burnett, Director of Speech Technologies

2. Why speech?
Ma Ma
Vok Say Oh
2 © Voxeo Corporation

3. Speech is the natural human interface
 15% of world population has a personal
computer
 Greater than 60% of world population has a
mobile phone
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4. What is communication?
Your
Customer
You
(Your speech-enabled IVR)
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5. Communication is natural?
249694
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6. But for IVRs . . .
Your
Customer
You
(Your untuned speech-enabled IVR)
© Voxeo Corporation

7. So why do we tune?
 For better communication, which leads to
 More satisfied customers
 Shorter call durations
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8. What can we tune?
Your untuned speech-enabled IVR
© Voxeo Corporation

9. What can we tune?
Your untuned speech-enabled IVR
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10. What we say – prompts
 Goal: naturally reduce variability in caller's
responses
 Because: predictability simplifies grammars
and increases recognition accuracy
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11. Prompt tuning
 Vocabulary
• Use the words your customers use
• For sales, say “sales”; For billing, say “billing”; ...
• Are you calling to learn more about our products, to
fix a problem with your bill, or …
 Keep in mind
• Speech allows your customer to describe things
THEIR way rather than to use your internal company
description
• Make it easier for them to do that!
© Voxeo Corporation

12. Prompt tuning
 Prompt specificity
• General: “What would you like?”
• More specific: “Which department would you like?”
• Precise: “Would you like A, B, C, or something else?”
 Keep in mind
• The caller will often use the exact words YOU use
© Voxeo Corporation

13. Ever heard this before?
 For Sales, press 1
 For Billing, press 2
 For option I can't remember, press 3
 For another option I can't remember, press 4
 For yet another option I can't remember, press 5
 For more of the same, press 6
 Blah blah, press 7
 For help with this menu, press 8
 To hear these options again, press 9
© Voxeo Corporation

14. Prompt tuning
 Prompt length
• Keep it short: less than a few sentences total, only
one of which asks for input
• Or: provide pauses (at least one second long) for
interruption
 Keep in mind
• Speech communication is only natural if it's not
drawn out
• Primacy and recency effects
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15. What can we tune?
Your untuned speech-enabled IVR
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16. What we listen for – grammars
 Goal: Cover everything they are likely to say,
and nothing more
 Because: Accuracy in grammar coverage
directly affects recognition accuracy
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17. Grammar tuning
 Cover everything they say
• Pre- and post- phrases such as please, I would like,
and thank you
• Synonyms such as (for yes/no) yeah, sure, absolutely
not
 Keep in mind
• Recognizers can only hear it if it's in the grammar
© Voxeo Corporation

18. Grammar tuning
 Include only what they say
• Write grammars that don't overgenerate
• If matching numbers/digits, only include valid strings
if at all possible
 Keep in mind
• Every unnecessary grammar phrase is a potential
misrecognition
© Voxeo Corporation

19. What can we tune?
Your untuned speech-enabled IVR
© Voxeo Corporation

20. How we listen – parameter optimization
 Goal: Optimize recognizer parameter settings
 Because: Better accuracy, of course!
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21. Parameter optimization – which parameters?
 Rejection threshold
 Endpointer settings (sensitivity)
 Large grammar parameters
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22. Rejection threshold – what is it?
False
Rejections
Misrecognitions
0
Rejection Threshold
100
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23. Rejection threshold – what is it?
Cutoff value for the recognizer confidence below False
which the speaker's utterance will be rejected
Rejections
Misrecognitions
0
Rejection Threshold
100
© Voxeo Corporation

24. Rejection threshold – total error
False
Rejections
Misrecognitions
0
Rejection Threshold
100
© Voxeo Corporation

25. Rejection threshold – comparison
ASR
Engine A
ASR
Engine B
0
Rejection Threshold
100
© Voxeo Corporation

26. Rejection threshold – comparison
ASR
Engine A
ASR
Engine B
Optimal thresholds
0
Rejection Threshold
100
© Voxeo Corporation

27. Rejection threshold – another
comparison
ASR
Engine A
Optimal thresholds
ASR
Engine B
0
Rejection Threshold
100
© Voxeo Corporation

28. Parameter optimization
 Rejection threshold
• Generally largest impact on accuracy
• Optimum varies across recognition engines
• Optimum varies by set of active grammars
 Keep in mind
• Optimizing the rejection threshold is the SINGLE
MOST IMPORTANT parameter tuning you can do
© Voxeo Corporation

29. Endpointer sensitivity
Your
Customer
You
(Your hard-of-hearing
speech-enabled IVR)
© Voxeo Corporation

30. Parameter optimization
 Endpointer sensitivity
• Second-largest impact on accuracy
• Unnecessarily high and low sensitivity are both bad
• Optimum should be set once, checked annually
 Keep in mind
• If the recognizer can't hear you, it can't understand
what you say
© Voxeo Corporation

31. Parameter optimization
 Large grammar parameters
• Typically need to be adjusted if grammar has more
than 5000 entries
• Typically consumes more memory and/or CPU
• Vary by ASR engine, so ask
 Keep in mind
• If your grammar has many options, your recognizer
needs to “think” more than the default settings
usually allow
© Voxeo Corporation

32. What can we tune?
Your untuned speech-enabled IVR
© Voxeo Corporation

33. Summary – Keep in mind
 Speech allows your customer to describe things THEIR way rather than to
use your internal company description – make it easy for them!
 The caller will often use the exact words YOU use
 Speech communication is only natural if it's not drawn out
 Recognizers can only hear it if it's in the grammar
 Every unnecessary grammar phrase is a potential misrecognition
 Optimizing the rejection threshold is the SINGLE MOST IMPORTANT
parameter tuning you can do
 If the recognizer can't hear you, it can't understand what you say
 If your grammar has many options, your recognizer needs to “think” more
than the default settings usually allow
© Voxeo Corporation

34. For help
34 © Voxeo Corporation

35. State of the Art/Best Practices in
Speech Technology
Dan Burnett, Director of Speech Technologies
dburnett@voxeo.com