AN2384 Freescale Semiconductor / Motorola, AN2384 Datasheet - Page 15

• Manufacturer Part Number: AN2384
• Description: Generic Tone Detection Using Teager-Kaiser Energy Operators on the StarCore SC140 Core
• Manufacturer: Freescale Semiconductor / Motorola

A potential digit is determined from every processed sample. A comparison between two consecutive digits occurs
every other sample (the detector works at 4 KHz with an 8 KHz sampled input). When a difference (potential edge)
is detected, the sample number is stored so that the calculation of the duration uses the previous edge index. This
duration is compared to the values defined by the Q.24 recommendation, and a decision is made. The detailed
implementation of the test is explained in the next section. At a sampling rate of 4 KHz, 40 ms corresponds to 160
samples. Because of the transition period (the transition state at the beginning and end of a given digit), the signal
and pause durations must be decreased. The values in the implementation are defined experimentally, as illustrated
in the plots shown in Figure 8. After a series of keys is tested, digits (
represented. The figures focus on one particular key, where transition periods appear at the beginning of the
detection of key 2. The signal characteristics of the first experiment are given by:
For this signal power (0 dBm0), the average of each part is:
Freescale Semiconductor
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Generic Tone Detection Using Teager-Kaiser Energy Operators on the StarCore SC140 Core, Rev. 1
Sampling rate: 4 KHz
Power of tone: 0 dBm0
Twist: 4 dB
SNR: 40 dB
Phase offset: 0
Detected key: 2
Detected key: 145 samples
Pause: 88 samples
Transitions: 9 samples
Detected Key: 121 Samples
Pause: 54 Samples
Transitions: 8 Samples
Duration of the Transitions
Figure 8. Plots of Experiments to Define Implementation Values
Time Duration: 23 ms
2
1
Detected Key: 190 Samples
Pause: 122 Samples
Transitions: 9 Samples
Duration of the Transitions
1
Time Duration: 40 ms
) and corresponding samples (
2
1
DTMF Detector on StarCore
2
) are
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