What constitutes noise nuisance

Doesn't sound as if you're causing that much nuisance - but, of course, I haven't heard it.
However.... my FiL complained about the people next to him and the son playing 1940s songs at all hours - so unlikely! We think that FiL had tinnitus and that his brain translated the sounds into something that he recognised, hence the 40s tunes. Maybe your neighbour has a similar problem or the noise is coming from elsewhere....

It would depend if more than one neighbour heard anything.

Its a situation I have had experience of when living a flat, and surrounded by a younger age group, mainly unemployed and could be drugs related.
The procedure is the housing Officer , should get the local authority environmental health dept. to investigate , by the way its mentioned the person who is the complainer has not followed that route, and had the relevant devices installed to monitor the noise level.

The downside is getting a written complaint given by the housing authority , as a warning, if the person making the noise has gone down that road.

Mick

All I was told is that they had received numerous complaints from this one neighbour and that it had been referred to environmental health but I have heard nothing from them and apparently the referral to them was done 3 weeks ago

If you are hard of hearing then I imagine that you will not consider the TV to be excessive. We have cordless headphones that can be used with the TV, so that might be worth considering. I would make a note of what action you are taking to reduce the noise then you can respond as and when they get back to you.

Since the complaint says [an unlikely] 24 hours a day, you might find it useful to keep a diary of when and what you watch on television and when you play music – with and without headphones.

Good advice from absent

May I also suggest, that if the neighbours are finding it so bad, that the housing officer suggests that they (the neighbours) actually make sound recordings of what they can hear, along with the dates and times they heard it.

Your neighbour(s) must be strange - if they reckon the noise was bad, why didn't they simply mention it to you? To report it to the council is rather heavy-handed.

My husband is hard of hearing, he uses two hearing aids.
My son bought him cordless headphones because the level of volume was too loud for me, this solved the problem.

Years ago I had a neighbour who came round complaining I had my TV on too loud. I said that couldn't be true it must be someone else I don't own a TV or radio. You should have seen the look on her face.