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Appendix 3 Detailed Audio Tests
Note: In tests between HDX 4500 units it was not possible to select audio protocols
so only a limited range could be tested.
Test 1:
Frequency response (-3 dB)
(Insert -6 dB signal at local site, measure at remote site)
Siren LPR
24Kbit/s
Siren LPR Stereo
48Kbit/s
Siren LPR Stereo
96Kbit/s
Siren LPR Stereo
128Kbit/s
12 KHz
12 KHz
14 KHz
22 KHz
When the frequency response was measured it was found to be quite uneven for all
audio protocols. The levels measured 0 dB at both 1KHz and 7 KHz but at mid-
band (i.e. 3.5 KHz) was -6dB indicating a notch in the frequency response between
these frequencies.
Test 2:
Headroom (measured on Siren 22
,
64Kbit/s connection)
(Insert increasing amplitude 1 KHz tone at local site, monitor for overload
distortion at the remote site auxiliary output.)
Overload occurs at:
+3 dBm
Test 3:
Audio level
(Insert 0dBm 1KHz tone at local site, monitor the received level at the remote site)
As the audio output is varied by the volume control this test could not be carried
out.
Test 4:
Echo Cancellation
Setup
The echo canceller is fully automatic in operation. The quality of echo
cancellation and doubletalk from the system was excellent.
Audio levels adequate? (Yes/No)
Yes
Audio quality acceptable? (Yes/No)
Yes
Echo cancellation acceptable?
(Yes/No)
Yes
Quality of double talk
Excellent
