Cinematography Mailing List - CML

CTDM - Beta PVV1P/Dockable Deck


We got a BetaSP camera with a PVV1P dockable deck, which unfortunately came without manual. I can work-out all the buttons, but there is one pushbutton marked CTMD (below the monitor/alarm-buttons). What does it do exactly? I saw if I push it, the image in the viewfinder changes, but I can't work-out what it should mean.

On another note, the playback of video only seems to go via the viewfinder. Is there a way to set it to go out via one of the video-outputs as well?


Martin Heffels
Filmmaker/DP/editor/filmschool techie
Sydney, Australia

"The world is on the move. Adopt, adapt, survive."


CTDM stands for Compressed Time Division Multiplex and is the mechanism by which the component analog video is actually recorded on the tape. when you press that button, the viewfinders divided in half: the left side shows the luminance signal (Y) and the right half shows the color difference signals (Pb, Pr). This playback mode can serve as a quick check to ensure that all of the recording circuits are working properly.

Dave Satin
Video Engineer

>but there is one pushbutton marked CTMD (below the monitor/alarm->buttons). What does it do exactly?


Your camera records in color but your viewfinder plays back in black and white. So how do you know that you've recorded color properly? When you check a tape you push the CTDM button and you see the red and blue signal side by side. If they are both there it means you've recorded color properly. If there is a problem, one of the pictures will show it.

The acronym stands for Compressed Time Domain Multiplexed which has to do with how these formats record information on the tape. Or said another way black and white TV existed before color and when color was invented it was a modification of what black and white was, not a new and different invention (hence why we have drop and non drop time code too). Luminance is recorded at a bandwidth of about 4.2 MHz. but the color differences R-Y and B-Y components are time compressed so that R-Y is laid down in 1/2 a field first then B-Y is recorded in the other 1/2 field next to it. Both are given about 1.5mz of bandwidth. This combination of signals is where the term 'multiplexed' comes from and one of the reasons why we get 4:2:2 in analog television.

Walter Graff
BlueSky, LLC

Thank you all for helping me out on my quest for the mysterious button!


Martin Heffels
Filmmaker/DP/editor/ (film school techie)
Sydney, Australia

Copyright © CML. All rights reserved.