Re: [Phys-l] 240 and 600 Hz

[John Denker <jsd@av8n.com>]

On 04/14/2011 01:55 PM, ludwik kowalski wrote:
> Some new High Definition TV sets  are designed for very high image
> refreshment rates, such as 240 Hz and even 600 Hz. This seems to be
> unnecessary; the refreshment rate for traditional movies has been 30
> Hz. Because of this I think that anything above 60 Hz is just waste
> of money. Do you agree?

There actually are advantages to the higher refresh rate.

The issue is aliasing.  A familiar example is the "wagon wheel
effect".

It could be argued that the aliasing depends on the frame rate
not the refresh rate, and that's partly true, but that's not
the whole story, for a couple of reasons:

 -- If the screen is used as a computer monitor (rather than as
  a TV), the frame rate could be very much higher than 60 Hz,
  whereupon the wagon wheel effect in your computer simulation
  is much less of a problem.

 -- Even when you have a movie coming across the wire with a
  60 Hz frame rate, there is actually a lot of interpolation
  going on in the MPEG decoder.  You're better off doing the
  interpolation using a digital filter running well above
  frame rate.  That is to say, given a 60 Hz frame rate and
  a 600 Hz refresh rate, you are not obliged to paint the
  same scene 10 times;  you can interpolate.

  This is analogous to the fact that your audio system does
  a lot of filtering (Dolby etc.) using digital filters that
  run well above audio frequencies.

  The idea is that even though there are some irreducible problems 
  associated with the frame rate, but you don't want the digital 
  filter rate to add to your problems.

==========

OTOH there is a point of diminishing returns.