2.3.  Hints for Using Learn Mode

The following hints are provided to help you use learn mode:

• If your final tone description is being falsely triggered by noise or voice, you can:
  • Change the qualification ID (by setting lm_qualid field in LM_PARM structure) for more immunity to noise and less sensitivity to the tone. See 6.2.  LM_PARM: Learn Mode Parameters for more information on how to set this value.
  • Increase the repetition count if the tone has a simple cadence. (If you increase the repetition count and then fail to detect the tone, your tone description may be for a complex-cadence tone; in this case, you must set the repetition count to 1.)
• To learn a particular tone, you may need to change the learning parameters. For example, when learning a cadence tone that contains a limited number of repetitions, you can reduce the number of learning samples or cadence repetitions specified in lm_frames field in LM_PARM structure. Another example is when learning a short continuous tone, you can reduce the continuous tone minimum on-time specified in lm_cnt_min in LM_PARM structure.
• If you get an EDX_TNINFO error, which means there is not enough tone information to do the learning, try increasing the number of frames in lm_frames field in LM_PARM structure. If you get an EDX_TNINVALID error, which means an invalid tone was detected, try lowering the lm_qualid field in LM_PARM structure. Learn mode requires that at least 5 frames/samples be used.
• The Learn Mode library uses 4 seconds as the default duration for learning continuous tones (rather than the minimum of 1 second). There are two reasons why the default duration for learning a continuous tone is 4 seconds: one is for learning the tone and the other is for using the final tone description for detection.
   
  A 4-second minimum duration is needed for learn mode to determine whether the tone is cadence or continuous (rarely does a cadence tone have a 4-second tone-on duration). If you want to learn a continuous tone in less than 4 seconds, you can set the lm_cadflag field in LM_PARM structure to 2 to specify a continuous tone, and then set the lm_cnt_min field to a value under 400 (10 ms units).
   
  A 4-second minimum duration may also be needed when using the final tone description for the continuous tone for detection. To prevent the continuous tone final tone description from detecting a cadence tone that has the same frequency range, the tone-on duration for the continuous tone must be greater than the tone-on duration for the cadence tone. A 4-second minimum duration helps prevent a detection overlap with a cadence tone. In this case, you may want to set a short minimum on-time to learn the frequency of the continuous tone, and then increase the on-time when you build the tone for detection. The continuous tone on-time must be greater than any cadence tone on-time of the same frequency.

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