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17
E: AUDIO TESTS (ITU standards only)
Tests 1-3 were carried out with test signals inserted into the AUX (Auxiliary) input.
Test 1: Frequency response (-3dB)
(Insert a -6dB signal at the local site, measure the frequency corresponding to an audio
level reduction of 3dB at the remote site from the level received when a 1kHz tone is
transmitted).
Siren™ 14, 24kbit/s Siren™ 14, 48kbit/s
14kHz 14kHz
Test 2: Headroom (measured on a Siren™ 14, 48kbit/s connection)
(Insert increasing amplitude 1kHz tone at local site, monitor for overload distortion at
remote site)
Overload occurs at: +10dBm
Test 3: Audio Level
(Insert -6dBm 1KHz tone at local site, monitor received level at remote site)
Measure the level on the VCR output with the local volume at mid range.
Remote site signal measures: -18dBm measured on audio output
Test 4: Echo Cancellation
Setup The echo canceller is fully automatic in operation.
Lecture Theatre Room
Audio levels adequate? (Y/N) Not tested Yes
Audio quality acceptable? (Y/N) Not tested Yes
Echo cancellation acceptable? (Y/N) Not tested Yes
Quality of double talk Not tested Very Good
Subjectively the quality of the Siren™ 14 audio and echo cancellation was excellent. The
provision of: audio level meters for the microphone and VCR inputs; level adjustment on
the VCR inputs and an internal tone generator, are all very useful operational features.