I've read somewhere that films are speeded up slightly when broadcast on TV to compensate for the difference in film frames per second and the broadcast signal frequency/ mains power frequency (introducing 4% speed up???)

If that's the case it makes you wonder whether many manufacturers and customers make too much of the quality of their systems. A 1% distortion  in audio used to be seen as outside the definition of 'Hi Fi'!

Graham

I have never heard about this, but it sounds interesting. 

Yes for PAL - or more correctly 50 fields / sec purposes. If the film is originally targeted for TV, then it may be filmed at 25 fps to begin with, which is a straightforward conversion for 50 Hz TV standards. The 4% increase in picture speed is usually far less annoying than the artifacts that would be created by a 24 fps -> 25 fps conversion, although it can be done nowadays. For audio, there are quite effective methods for altering the pitch so you don't notice an increase there even if the frame rate has been increased.

This is a slightly easier problem for NTSC (or again more correctly, 60 Hz standards). Read more you than you ever wanted to hear here.

tournedos:

 Read more you than you ever wanted to hear here.

I thought this was common knowledge!

tournedos:

Yes for PAL - or more correctly 50 fields / sec purposes. If the film is originally targeted for TV, then it may be filmed at 25 fps to begin with, which is a straightforward conversion for 50 Hz TV standards. The 4% increase in picture speed is usually far less annoying than the artifacts that would be created by a 24 fps -> 25 fps conversion, although it can be done nowadays. For audio, there are quite effective methods for altering the pitch so you don't notice an increase there even if the frame rate has been increased.

This is a slightly easier problem for NTSC (or again more correctly, 60 Hz standards). Read more you than you ever wanted to hear here.

Thanks. Looked at the Wikepedia link. I think this all still comes back to the argument that your receiver/TV should not itself add unnecessary  further distortion etc but the reality is that a lot of original material does suffer in its preparation for broadcast..... and so you shouldn't get too hung up on exact reproduction of something that is already distorted. Having said that on the audio front a lot of material is now recorded loud and flat, so again you really want your equipment to be clever enough to somehow undo the damage already done in the production and broadcasting!

Graham