Diana, although 'switching' is indeed used in telephony, the more common usage in audi/video is 'patching' (normally, non-countable) --- it means a system of interconnecting ins and outs in different configurations easily, usually (or traditionally, at least) by means of 'flying leads' (patch cords) that are plugged between pairs of sockets (think of an old-fashioned manual telephone exchange!). Nowadays there exist alternative methods too, often 'virtual'

Remember that the root meaning of 'brasser' is 'to combine or mix ingredients'

Here's some confirmation from a quick Google:

Product Category GHIELMETTI DIGITAL/ANALOGUE PATCH PANELS

45-921 GHIELMETTI ASF-1 X 32AV3/1LA Blueline,
45-994 GHIELMETTI PLUG PARK 2 X 48 Anthracite.
45-930 GHIELMETTI NORMALLING PLUG Black ...
www.canford.co.uk/commerce/ category_3000558_3000050.aspx

In your second example, where you have 'brassages' in the plural, you must not saying 'patching' in EN! Keep it in the singular.

However, in your FIRST example, I believe they are referring, not to the 'concept of patching', but rather, to the physical equipment itself; if this is truly the case, then I would translate by either 'patch panels' or patch fields' (if they seem to be quite extensive, as would be implied by the fact that ALL audio, video and 'ordre' (?) signals have to pass through them --- quite a lot!

As for that 'en coupure', I'm not familiar with the term in French, but can think of 2 logical technical interpretations in EN.
1) It might mean that all this 'equipment must be connected via patch fields without normalling' --- this means that there are NO connections normally pre-made (as is more usual) --- this would mean that in your case, if you unplug all the patch cords, no signals pass through. [the more usual case is where signals are connected to the patch panel via switch contacts, in such a way that if you pull out all the cables, you default to a 'standard' connection configuration, and then you add patch cables (/cords) in order to 'over-patch' for non-standard operation. This is called 'normal through' or simply 'normalled' operation]

2) It might mean that 'the equipment is connect via patch fields in half-normal mode' --- this means that it is partly 'normalled', but overpatching on some circuits will cut off the normal(ly connected) feed --- this may be on inputs, on outputs, or a mixture of both.

I'm afraid by guesswork I can't tell you which it could be (or indeed, if there are any other possibilities), so it will need either some more distant context to give us a clue, or else a French AV expert to interpret this for us!

By the way, 'brassage' is already in the glossary, I've answered this one before!