Is 'silent' noise…killing your recording system?

[Last Updated: September 2016]

What can go wrong and why?

If you haven’t heard of ‘silent noise’ or the problems it can cause, here is a quick overview. Silent noise is sub-audible activity on a telephone line also referred to as ‘mains-hum’. You can’t hear it but telephone systems and call recorders can. If your call recorder is set to record when it hears conversation activity on the line, it can also kick into record when it hears silent noise and this produces an array of problems for the user. The most common problems manifest themselves as ‘phantom calls’ and ‘excessive storage’ demands.
Phantom calls are generated when silent noise is present and this produces a recording that is logged into the database as a genuine call. All appears to be correct until an operator goes to replay the call and then finds there is nothing there. If phantom calls appear on a regular basis they clog up the system and waste huge amounts of operator time trying to separate the real calls from the phantoms. In extreme cases phantom calls can be so numerous they almost render a system inoperable and so replays are abandoned.
Excessive storage is a natural symptom of phantom calls or where genuine calls have silent noise contamination (ie extended length); the manifestation is rapid usage of hard disk space or excessive tape/DVD changing.
There are three solutions to silent noise and here they are:- 1) change your lines, 2) balance your recorder, 3) fit a noise filter.

1) Change your lines:- Silent noise is only present on analogue lines or extensions, therefore if you are planning to upgrade your telephone lines don’t waste time – do it, life will be so much easier. You will need to match your recorder to the new lines so check out all the angles first before you start.

2) Balance your recorder:- You will need an engineer to do this for you. He will balance the threshold of when the recorder activates for a genuine conversation verses when it will activate with silent noise. In essence it is a trade-off and in most instances it works well but problems can occur with quietly spoken individuals and latency.

3) Fit a noise filter:- A noise filter or ‘line conditioning unit’ can go a long way to clean up noisy lines; using this in conjunction with recorder balancing it is possible to completely cure the problem. There are of course limitations to the amount of filtering that can be done and excessively noise lines will defeat the filter.

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