7 DTX test sequences

06.073GPPHalf Rate Speech: Test Sequence for GSM Half Rate Speech CodecTS

This clause describes the test sequences designed to exercise the VAD algorithm (GSM 06.42 [6]), comfort noise (GSM 06.22 [4]) and discontinuous transmission (GSM 06.41 [5]).

7.1 Codec configuration

The VAD, comfort noise and discontinuous transmission shall be tested in conjunction with the speech encoder [2]). The speech encoder shall be configured to operate in the DTX mode defined in GSM 06.22 [4].

7.2 DTX test sequences

Each DTX test sequence consists of four files:

‑ Files for input to the GSM half rate speech encoder: *.INP

‑ Files for comparison with the encoder output *.COD

‑ Files for input to the GSM half rate speech decoder: *.DEC

‑ Files for comparison with the decoder output: *.OUT

The *.DEC files are generated from the corresponding *.COD files.

In a correct implementation, the speech encoder parameters generated by the *.INP file shall be identical to those specified in the *.COD file; and the speech decoder output generated by the *.DEC file shall be identical to that specified in the *.OUT file.

Table 6 lists the DTX test sequences and their size in frames.

7.2.1 Predictor values computation

The computation of the predictor values described in GSM 06.42 [6] is not tested explicitly, since the results from the computation are tested many times via the spectral comparison and threshold adaptation tests.

7.2.2 Spectral comparison

The spectral comparison algorithm described in GSM 06.42 [6] is tested by the following test sequence:

‑ DTX01.*

7.2.3 Threshold adaptation

The threshold adaptation algorithm described in GSM 06.42 [6] is tested by the following test sequence:

‑ DTX02.*

7.2.4 Periodicity detection

The periodicity detection algorithm described in GSM 06.42 [6] is tested by the following test sequence:

‑ DTX03.*

7.2.5 Tone detection

The tone detection algorithm described in GSM 06.42 [6] is tested by the following test sequence:

‑ DTX04.*

7.2.6 Safety and initialization

This sequence checks the safety paths used to prevent zero values being passed to the norm function. It checks the functions described in the adaptive filtering and energy computation, and the prediction values computation given in GSM 06.42 [6]. This sequence also checks the initialization of thvad and the rvad array:

‑ DTX05.*

7.2.7 Comfort noise test sequence

The test sequences described in sub‑clauses 7.2.2 to 7.2.6 are designed to exercise the VAD described in GSM 06.42 [6] and the discontinuous transmission described in GSM 06.41 [5]. The following test sequence is defined to exercise the comfort noise algorithm described in GSM 06.22 [4]:

‑ DTX06.*

7.2.8 Real speech and tones

The test sequences cannot be guaranteed to find every possible error. There is therefore a small possibility that an incorrect implementation produces the correct output for the test sequences, but fails with real signals. Consequently, an extra sequence is included, which consists of very clean speech, barely detectable speech and a swept frequency tone:

‑ DTX07.*

NOTE: Some of the DTX test sequences contain homing frames. The DTX test sequences are therefore only suitable for testing a single transcoding.

Table 6: Location and size of DTX test sequences

size

(bytes)

Disk No.

File Name

No. of Frames

*.INP

*.COD

*.DEC

*.OUT

3

DTX01

460

147 200

18 400

20 240

147 200

3

DTX02

886

283 520

35 440

38 984

283 520

3

DTX03

125

40 000

5 000

5 500

40 000

3

DTX04

317

101 440

12 680

13 948

101 440

3

DTX05

37

11 840

1 480

1 628

11 840

4

DTX06

240

76 800

9 600

10 560

76 800

4

DTX07

1 188

380 160

47 520

52 272

380 160