Appendix 3 Detailed Audio Tests - Polycom HDX 4500 Appendix

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
12 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
(Insert increasing amplitude 1 KHz tone at local site, monitor for overload
distortion at the remote site auxiliary output.)
Overload occurs at:
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)
Audio quality acceptable? (Yes/No)
Echo cancellation acceptable?
Siren LPR Stereo
48Kbit/s
12 KHz
+3 dBm
(Yes/No)
Quality of double talk
20
Siren LPR Stereo
96Kbit/s
14 KHz
22, 64Kbit/s connection)
Yes
Yes
Yes
Excellent
Siren LPR Stereo
128Kbit/s
22 KHz