6.6.  TN_FREQ: Tone Frequency

The TN_FREQ structure is declared as follows:

typedef  struct {

   unsigned short int tn_freq1;        /* 1st tone frequency */

   unsigned short int tn_fq1dev;       /* 1st tone deviation */

   unsigned short int tn_freq2;        /* 2nd tone frequency */

   unsigned short int tn_fq2dev;       /* 2nd tone deviation */

} TN_FREQ;

The TN_FREQ structure specifies frequency information for a tone and is a member of the TN_DESC structure.

The TN_DESC structure is used in two different parameters of the lm_LearnTone( ) function, and serves the following purposes:

• tn_rangep (input): Specifies optional tone learning boundaries as input to the lm_LearnTone( ) function, restricting learning to the specified range.
• tn_tonep (input): Specifies an existing tone description as optional input to the lm_LearnTone( ) function, and which learn mode incorporates in the final tone description.
• tn_tonep (output): Provides the final tone description that is returned by lm_LearnTone( ).

Use the lm_clrdesc( ) function to clear the fields of a TN_DESC structure, including the fields in the TN_FREQ and TN_DUR structures.

Table 5.  TN_FREQ Structure

Field	Description
tn_freq1	Length: 2 (unsigned short int). Units: Hz. Range: 300 Hz -- 3000 Hz. Tone 1 Frequency: Specifies the frequency of the first tone in Hz. This information serves different purposes depending upon where the TN_DESC structure is specified:
	For tn_tonep Existing Tone Input: Set this field to a non-zero value to adjust an existing tone description with the lm_LearnTone( ) function; you must specify in tn_tonep the complete tone description to be adjusted (also, make sure to set the dflagp location to specify a flag value for a single or dual tone).
	For tn_tonep New Tone Input: Set this field to zero to learn a new tone with the lm_LearnTone( ) function; you must set the dflagp location to specify a flag value for a single or dual tone.
	For tn_tonep Output: When lm_LearnTone( ) is complete, this field returns frequency information for the final tone description.
	For tn_rangep Input: Set this field to a non-zero value to restrict the learning range; you must set lm_cadflag field in LM_PARM structure to indicate cadence or continuous if you do this.
tn_fq1dev	Length: 2 (unsigned short int). Units: Hz. Tone 1 Frequency Deviation: Specifies the frequency deviation of the first tone in Hz. This deviation is subtracted from and added to tn_freq1 to define the tone detection range.
tn_freq2	Length: 2 (unsigned short int). Units: Hz. Range: 300 Hz -- 3000 Hz. Tone 2 Frequency: Specifies the frequency of the second tone in Hz.
	0: Indicates there is no second tone (signal is a single tone).
tn_fq2dev	Length: 2 (unsigned short int). Units: Hz. Tone 2 Frequency Deviation: Specifies the frequency deviation of the second tone in Hz. This deviation is subtracted from and added to tn_freq2 to define the tone detection range.

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