Why did 405 look so good?

[Terry]

My biggest concern over 405 was the prevalent line whistle which I found really irritating.

Interesting. My experience is that, because of the frequency accuracy of the 10,125Hz timebase frequency, the brain develops a mental notch filter which is quite effective.

I remember returning home after a fortnight's holiday in which I didn't see a single TV and being greeted by a very loud timebase whistle the moment I entered the living room. My brain had obviously 'forgotten' about the timebase whistle during the break but rebuilt the notch filter very quickly, after which I could ignore it as usual.

Perhaps your brain wasn't so good in the notch filter department or you had exceptionally good hearing?

To add to the notch filter theory, if the timebase frequency varied, it became instantly audible.

I'm sure we have members who have no experience of the heyday of 405-line TV, so I'll explain the next bit in detail.

We didn't have any lightweight portable broadcast quality TV cameras back in 405 days, so external sequences were filmed and telecine machines used to generate the TV signal for insertion into the main programme. The chances were that the telecine room would be on a different mains phase to the studio, even if they were both in the same building, so there could be a considerable difference in the field sync timing between the local and remote signals. To avoid a visually annoying sync switch, the practice was to switch the studio sync reference from the mains to the incoming video in preparation for the playout of the film clip which could cause a sudden change in line frequency until the two signals were in sync.

Hum in receivers could cause a number of invisible problems - invisible, that is, until the field sync timing changed. This could be just a rolling hum bar, an S ripple running through the line sync, making even static people look as if there doing a hula-hula dance or a very strange effect if the ripple caused a change in the field linearity!

One night I was engriossed in a book while mum was watching something on the TV, which was behind and to one side of me, when one of these re-syncing events occurred. As soon as the line frequency started to change, it 'jumped out' of the notch and instantly became subjectively much louder.

Although I knew exactly what was going on, I intinctively glanced over my shoulder at the ripple running up the screen.  "How did you know that was going to happen?" asked mum.

Mum never could hear the timebase whistle!