EXFO FTB-635 Wideband Copper and DSL Test Module - Manual (Page 248)

Noise Tests
240 FTB-635
VF Noise Test
Summary
The VF noise tests provides you a quick and simple indication of level of
voice band noise on the circuit. In general values greater than 20 DBRNc
affect service and can be heard by the customer. Metallic faults and bad VF
Balance are the typical causes of VF Noise, although high external sources
or Power Influence can also cause too much noise on an otherwise good
pair.
Summary tab displays the pass/fail status of the tests executed. Refer
Copper Tests: Result Summary on page 291 for more information.