At what point in the process was vertical low pass applied?

[90sTV]

I've read that video meant to be viewed on interlaced displays is/was filtered in the vertical dimension because it would cause "twittering" otherwise, which is the reason true progressive video (not low-pass filtered) is said to have 30% higher vertical resolution than equivalent interlaced video. For instance, a true 480p would have 30% higher vertical resolution than 480i.

However, at what point in the production chain was the low pass filter applied? Let's say a TV series was shot on film and then telecined to either beta sp or 1-inch tape for a cable broadcast. Were the tapes containing the content already low-pass filtered, or was it low-pass filtered when they sent out the signal?

[Skiller]

It was low-passed the moment it was telecined, in other words the moment the film was scanned and transferred to any analog or digital standard definition format such as Beta.

[newpball]

The times certainly have changed, in the old days engineers got away with "explaining" people that low pass filters enhance the video, nowadays people know better!