Interlacing and channel bandwidth

[ppppenguin]

30psf isn't actually in the list of SMPTE standards Implicitly 25psf has been used for years in Europe for film material where 24fps film has traditionally been shown at 25fps. The 4% fater running time is just accepted as normal, the sound pitch likewise or it can be corrected.

The US has suffered badly from its standards. 59.9Hz fouls up timecode for the prodcution people. 3:2 pulldown fouls up transmission of 24fps film. This can be overcome with advanced standards converters. These can convert 24Hz material to 30Hz without significant quality loss. They can also recognise and remove 3:2 artefacts.

[NewVista]

Originally Posted by ppppenguin

.. 59.9Hz fouls up timecode for the prodcution people..

Were there problems editing with dropframe timecode?

[ppppenguin]

Drop frame doesn't work too badly on short programmes, as all editing software has been designed to cope with its peculiarities. Generating it in the long term requires all sorts of corrections as there is no simple relationship between clock time and dropframe TC.

It's all due to a decision made at the start of NTSC colour, long before TC was invented. The relationship beween colour SC and sound carrier had to be set to minimise certain crossmodulation problems. It was felt that moving the sound carrier by 0.1% would upset too many existing receivers so they moved H, V and SC frequencies instead. We've been living with the consequences ever since TC was invented.

[cbenham]

Originally Posted by ppppenguin

Drop frame doesn't work too badly on short programmes, as all editing software has been designed to cope with its peculiarities. Generating it in the long term requires all sorts of corrections as there is no simple relationship between clock time and dropframe TC.

It's all due to a decision made at the start of NTSC colour, long before TC was invented. The relationship beween colour SC and sound carrier had to be set to minimise certain crossmodulation problems. It was felt that moving the sound carrier by 0.1% would upset too many existing receivers so they moved H, V and SC frequencies instead. We've been living with the consequences ever since TC was invented.

The original color subcarrier frequency tested by RCA was 3.583125 MHZ which worked perfectly with 60/15750 on color receivers. However it caused visible moire patterns in received images on B&W intercarrier receivers during the tests because it beat against the 4.5 MHZ audio subcarrier.

Changing the H & V frequencies slightly to 15734.26 and 59.94 and reducing the color subcarrier to 3.579545 MHZ resolved the problem for the B&W sets, although it was never a problem for the new color sets.

Much Later, this change proved to be the undoing of videotape editing, special effects, standards conversion, and digital video.

Life in the engineering department would have been so much easier if they'd left it alone.
Cliff