AN2384 Freescale Semiconductor / Motorola, AN2384 Datasheet - Page 26

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

Conclusion
8
This application note presents the theory and design of a generic tone detector based on the Teager-Kaiser (TK)
energy operator along with its practical application within the context of a DTMF detector. It explains the practical
implementation details and describes the extensive test methodology and results.
The DTMF detector implementation on the Freescale SC140 core has two major components: initialization
(fsl_dtmf_det_init) and actual detection (fsl_dtmf_det). The first component initializes the states of the channel-
dependent data structure of the detector. The core of the DTMF tone detector (second component) relies on TK
energy operators.
The core detection process works at 4 KHz, on a per-sample basis, with a block of input samples. One intrinsic
feature of this implementation is that samples do not have to be buffered prior to the detection and decision parts of
the algorithm. Consequently, the program could be adapted to run without any input buffer by changing the AGC.
The algorithm is easily tuned, and extending it to other signaling standards, such as MF-R1 and MF-R2, is fairly
straightforward. Because of the simplicity of the implementation and the architectural advantages of the MSC8101,
the module requires low average MCPS and memory. These features make the TK energy operator implementation
an attractive alternative to conventional algorithms, such as Goertzel filters, and consequently favor its use in
multi-channel infrastructure applications such as media gateways. The proposed method passed all the major tests,
including Mitel, BellCore, and CSELT, proving to be robust in terms of frequency tolerance, twist, power level,
guard time, SNR, and talk-off. All available tests for Q.24 recommendation passed (section 2 of Q.24, with the
exception of 2.7 to 2.9).
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Conclusion
Generic Tone Detection Using Teager-Kaiser Energy Operators on the StarCore SC140 Core, Rev. 1
CSELT Talk-off test. This test is a 20-minute highly condensed recording of sounds from
conversations. The speech bursts are 150 ms each. The CSELT documentation does not directly state
what an acceptable talk-off response is. The ETSI specification for DTMF transmitters and receivers
[10] allows five responses for this test. The test passed.
Bellcore tests. Six 30-minute recordings compose this talk-off test. Detected keys are counted in-
groups, with a maximum number of detects allowed in each group. The test passed.
Key Groups
Set-up 1
Set-up 2
Set-up 3
Norm
Table 12. Mitel Side 2 Test 2 Results Summary
Set-up 1
Set-up 1
Table 13. CSELT Talk-off Test Summary
1 (P)
0 (P)
Table 14. Bellcore Tests Summary
0 to 9
<333
9 (P)
9 (P)
9 (P)
Set-up 2
Set-up 2
1 (P)
0 (P)
0 to 9, * and #
<500
9 (P)
9 (P)
9 (P)
Set-up 3
Set-up 3
1 (P)
0 (P)
All 16 digits
<666
9 (P)
9 (P)
9 (P)
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