AN2384 Freescale Semiconductor / Motorola, AN2384 Datasheet - Page 23

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

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The DTMF detection algorithm is written in a mixture of both ANSI C and MSC8101 assembly code. The
complete module, along with drivers for peripherals (that is, ethernet and codec), is a Metrowerks project using
version 1.5 of Metrowerks IDE for Starcore SC140. This code runs in real time on the MSC8101ADS [4].
Mitel tests [7], Centro Studi E Laboratori Telecomunicazionis (CSELT) talk-off tests, and Bellcore talk-off tests [8]
were performed. On the hardware set-ups illustrated in Figure 12, the three following methods of testing were
used:
Testing results are listed in detail as follows with (P) indicating Q.24 compliance (see Table 7):
Freescale Semiconductor
DTMF Q.24 Compliance Tests
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Generic Tone Detection Using Teager-Kaiser Energy Operators on the StarCore SC140 Core, Rev. 1
Data
Connection
Set-up 1. Ethernet digital PCM linear data. Audio files are sent to the detector via the 100 Mbit
Ethernet port. Sample quality remains high. Detected keys are stored in an array and written into a file
at the end of the process.
Set-up 2. Ethernet digital A/ -Law encoded data with the same device as Set-up 1.
Set-up 3. Linear codec analog linear data. The MSC8101ADS codec is described in [9]. Before testing
of the detector, the noise added by the codec was analyzed to ensure that it was not excessive. Audio
files are played by the PC sound card, which is then plugged in to the codec input.
Mitel Side 1 Test 2: Decode Test Digits. Decode test digits 1 to 16 (10 pulses each). In all cases, all
digits are detected. The test passed.
Mitel Side 1 Test 3: Bandwidth and center frequency check. This test determines the receiver
recognition bandwidth (RRB) and receiver channel center frequency offset (RCFO) for both the H and
L frequency for the keys 1, 5, 9, and D.
ITU-T Q.24 recommends that a frequency deviation of less than or equal to 1.5 percent must be
recognized as a valid digit and a deviation of more than 3.5 percent must be considered as a non-valid
digit. Thus, a passing score on a given item must be between 15 and 34 detects. This test includes the
result of the calibration tone in Side 1 Test 1, which was measured to be 1000 Hz. This test shows
results consistent with the talk-off test results presented later. The test passed.
Set-up 1 and 2
MSC8101
Ethernet Port
Figure 12. Testing Set-ups
MSC8101
I/O
Data
Connection
Codec
Audio Source from
PC Sound Card to
IN-L Audio Entry
Set-up 3
DTMF Q.24 Compliance Tests
Audio Loopback
MSC8101
(optional)
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