Microchip Technology dsPIC DSC DTMF, Руководство пользователя

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dsPIC
®
DSC DTMF Detection Library User’s Guide
DS70332A-page 8
©
2008 Microchip Technology Inc.
1.3 PRINCIPLE OF DETECTION
Figure 1-1 shows the shape of a typical DTMF signal. The signal detection process
involves the following major stages:
• Tone Detection phase
• Silence Detection phase
FIGURE 1-1: DTMF TONE
The Tone Detection phase analyzes the spectral properties of a signal and validates
the DTMF tone. The Tone Detection phase is followed by the Silence Detection phase.
The Silence Detection phase measures the minimum silence duration for the tone
validation. The shape of a DTMF tone is a result of the combination of these two
phases. This tone also includes the Pause period.
1.3.1 Tone Validation Test
The Shape test is a Tone Validation test. It is also called the Silence test. It ensures that
the spectral properties and the shape of the incoming signal match the DTMF signal
properties. The Shape test improves the rejection capability of the detector by rejecting
the speech and music signals that are similar to a DTMF tone. Thus, it avoids false tone
detections. However, the most important part of the detection process is the Tone
Detection phase, which involves the analysis of the spectral properties of a signal.