Call progress tone detection performance specifications

Table 1 shows the performance specification met by Blueworx Voice Response call progress tone detection. However, note that the performance is degraded in noisy telephony environments.

The call progress tones detector that Blueworx Voice Response uses can detect a single tone, dual tones, or voice energy. The tones must meet the following criteria:

A tone must be less then 2000 Hz.
The sum of the tones must be less than 1500 Hz. (If the sum of the frequencies is greater than 1500 Hz, the detector reports the average frequency. The same is true if the two tones are close in frequency; for example, 400 Hz and 430 Hz.)

The detector evaluates the ratio of peak energy to average energy. For a single tone, the ratio is 1:1; for a dual tone, the ratio is 2:1; and for voice energy, the ratio is greater than or equal to 5:1. The audio energy is sampled every 20 ms.

The detector uses "curve fitting" to identify frequencies and energy levels. For example, if two tones are detected, the detector attempts to fit a curve for two tones. If the sum of the frequencies is greater than 1500 Hz, the detector reports the average frequency. With voice energy, the detector reports the amount of time the energy is greater than the value set for the Constant Energy Minimum system parameter.

Continuous tones are detected using the detector's “immediate mode”, which samples the tones every 100 ms instead of every 20 ms. Only frequencies and energy levels are reported.

Attention

In evaluating tones, Blueworx Voice Response searches for the first appearance of the tone in the Call Progress Tones parameter group, beginning with Tone Id 1 (see How call progress tones are identified). For this reason, it is very important that the range that is specified by minimum and maximum values for one frequency does not overlap the range that is specified by the values for another frequency with a different Tone Id number.

Table 1. Call progress tone detection performance specifications.
This table shows level, frequency, and cadence specifications for single, dual, and tritone tone types.
Parameter	Tone Type
Parameter	Single	Dual	Tritone
Level (dBm) (+ or - 2.5 dB)	+6 to -43	-10 to - 43 or - 10 to - 34¹	+6 to -43
Frequency (Hz) (+ or - 2.5%)	200 to 2000	200 to 900²	200 to 2000
Cadence³	Continuous or cadenced	Continuous or cadenced	Sequential single tone
Note: -10 to -34 if the frequency difference is 30 to 50 Hz; -10 to -43 if the frequency difference is greater than 50 Hz. A reduction in dynamic range occurs when the frequency difference for the two tones is less than 50 Hz. An example is U.S. dial tone, which consists of 440 Hz and 480 Hz components. If the sum of the frequencies is greater than 1500 Hz, the detector reports the average frequency. The same is true if the two tones are close in frequency, for example, 400 Hz and 430 Hz. The minimum on and off periods are 60 ms. The maximum on and off periods are 5 seconds.