Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
[Help] "Time compressed" LaserDisc pulldown
#1
I have a fairly simple and specific question, relating to the posts I've quoted below for the sake of context:

How much time compression is actually applied to "time compressed" NTSC LaserDiscs? Is it a set thing, or does it vary depending on how much it needs to be condensed to fit onto a 2-sided CLV disc? As in, PAL speedup is about 4% (with 24 frames per second being sped up to 25 frames per second and then converted to 50 interlaced fields per second); how much faster does a time-compressed NTSC LD player back compared to a standard telecined 60/1001 fields per second NTSC LD? For PAL, I've been using RX to do a 2-step resampling operation to fix the speed very precisely, as follows:

1. Calculate ratio between source media frame rate and intended target frame rate, then translate to audio sample rates to determine how much adjustment is needed:

Film is 24 fps, but my intended delivery frame rate is NTSC 24000/1001 fps, meaning that the ratio between PAL and my delivery format is (24000/1001) : 25 fps
Expressed as a fraction instead that's (24000/1001) / 25

To convert to audio samples, just multiple that ratio by the sample rate. Audio sample rate is whatever it's recorded at, let's say it's 48 kHz, in which case:

(24000/1001) / 25 x 48000 = 46,033.966... (rounded is 46034 Hz)

2. In RX, resample using "change tag only" to calculated sample rate first, which doesn't actually resample the audio as such (as in the samples are not altered, they're just played back at a different rate)

3. Once finished with whatever editing is being done, apply a second resample, but this time actually adjusting the samples themselves (as in, *not* ticking "change tag only") such that the speed is not adjusted but the samples themselves are, at accuracy afforded by RX autoconverting to 32-bit float

4. Dither back to desired delivery bit depth (e.g. 24 or 16)


So, I'd likely be using this same method, but in order to know the amount of adjustment required I'd have to know the precise amount of speedup / time compression / whatever you want to call it.


Context below so you know why I'm asking. Basically, I've got one time-compressed LD on the way and I don't know how much adjustment is correct. I could attempt with trial and error to figure out how much tweaking is needed to line it up, but if anybody actually knows (if it's actually a standard thing rather than a case-by-case adjustment) it would obviously be good to confirm the proper amount of adjustment.


(2020-10-11, 05:21 AM)pipefan413 Wrote: Jeeeeeeesus... finished figuring out the structure of THE EXORCIST resync and I kinda want to dig a big hole and jump into it because, to quote my own AviSynth notes...

pipefan413 Wrote:# 34 + 35 = 69 frames missing at 1st reel change
# 33 + 28 = 61 frames missing at 2nd reel change
# 1 + 8 = 9 frames missing at 1st LD side change
# 12 + 9 = 21 frames missing at 3rd reel change
# 25 + 19 = 44 frames missing at 4th reel change
# 31 + 11 = 42 frames missing at 5th reel change
# 10 frames missing at 2nd (final) LD side change
# 10 + 9 = 19 frames missing at 6th (final) reel change

# Total missing frames:
# 69 + 61 + 9 + 21 + 44 + 42 + 10 + 19 = 275
# 275 / (24000/1001) = 11.470 seconds (!)
# x 48000 = 550,550 samples at 48 kHz

Sick

No wonder @The Aluminum Falcon was struggling to make it work well! I dunno how the hell he managed what he did, looking at the sizes of the holes in the LD source. Bloody hell.

We're really talking about gaps that are way too large to bridge with extension crossfades, I think, and there is no alternative source that I know of apart from my other LD copy (which is the first pressing of the same disc, so almost certainly has identical frames). If I were to attempt to patch this, I'd have to create a custom mono downmix from something else, like one of the 5.1 mixes or perhaps preferably a 2.0 track from something else like one of the newer LDs. But even that is kind of a potential s**tshow; it may not be a transparent transition regardless of what I do with it.
(2020-10-11, 07:12 PM)pipefan413 Wrote: The trouble here is that there is actual dialogue and other conspicuous audio lost in these big holes at the reel / side changes. For instance, here is the first reel change:


pw = Pazuzu

If you look closely, you can see Regan's mouth moving before we hear her speak; on the OOP DVDs and other non-mono transfers, she says "Here it comes..." before she then says "... there!", but those frames are missing from the mono transfer. So I can't just leave it silent, it needs a patch over. The other reel changes are generally similar; there's another one at the moment where the bed is chucking her about ("Mother! Make it stop!") and Chris jumps on the bed to try to weigh it down or whatever, which again is a very noisy moment where they're both yelling and screaming and the bed is rattling so I can't just stretch it out or leave it silent or whatever.

So I'm on the hunt for alternative audio sources to patch over the massive holes in the mono track. What I'm thinking is that if I can find another LaserDisc with an older audio source than the modern transfers but hopefully without the missing frames (or at least without *some* of the missing frames), I can downmix the Dolby Surround track to 1.0, duplicate it to dual mono 2.0, and then very carefully patch the gaps as seamlessly as possible. Whilst I will likely record this digitally as well for posterity, I will most likely do the recording in analogue to slightly better match it to the mono, though it won't be as manky as an actual mono audio track as it'll be turning the digital track to analogue output rather than playing back an analogue track which has no noise reduction on it (which is what the mono track is, being pre-CX). I may even take it a step further and take a leaf out of Belbucus' book: record the digital audio, then record it to tape (either audio casette or VHS) and back again, to intentionally introduce tape hiss to better match the actual mono mix.

In other words: this has turned into a significantly bigger job than I expected, which *might* mean I can't get it done before Halloween. But the poll's still open anyway, so I guess Halloween or one of the other options might edge it out regardless!
(2020-10-16, 11:02 PM)pipefan413 Wrote: Now capturing 1993 US fullscreen LaserDisc 1007. Apart from possibly using this as a syncing reference, I may as well sync it to the Blu-ray and the now out of print fullscreen DVD, which I previous said I suspected was sourced from the exact same master (and seeing it now in front of me, I'm pretty sure I was right about that). But I'm very curious to see what this 1996 JP one PILF-2196 looks and sounds like, given that it seemingly makes no reference to Dolby Surround at all (just says it's stereo).

For patching purposes I'm most likely going to use the 48 kHz analogue stereo recordings even though - and indeed, specifically because - they will sound worse than the bit-perfect 44.1 kHz digital captures. I'm hoping this'll help a little with blending to the analogue mono recording, though the 1985 mono one will still sound worse because it's from an older and significantly more beaten-up print source than the much later 1993 disc. As expected, the side changes are in different places, which is of course good news because it means audio will not be missing from the same places.

Summary of THE EXORCIST LaserDiscs I have captured or will capture:

1983, US [1007 LV]
Original time-compressed fullscreen transfer with analogue mono. I anticipate this to be useful for side-changes at best, nothing more (since it's almost certainly from the same source as the two JP analogue mono LDs, and will presumably have the same missing frames in addition to the extra pulldown from time compression)

1985, JP [10JL-1007]
First fullscreen release with analogue mono that wasn't time-compressed (unlike 1983 US release 1007-LV)

1989, JP [NJEL-01007]
"Ever Green" reissue of 10JL-1007

1993, US [1007]
Digitally remastered fullscreen re-release, this time with digital Dolby Surround instead of analogue mono, I believe most likely sourced from the 1979 theatrical re-release's 35 mm Dolby Stereo track. I believe the video is functionally identical to or at least sourced from the same master as the fullscreen transfer on one side of the now out of print double-sided 1997 US DVD.

1996, JP [PILF-2196]
Digitally remastered widescreen re-release, which curiously only lists the audio as "stereo" and makes no mention whatsoever of Dolby Surround / Pro Logic. I'm wonder if it's a unique mix, strange as that would be, and if it is plain old stereo rather than Dolby matrixed it's most likely a better patching source for the analogue mono than the Dolby Surround track.
Reply
Thanks given by:
#2
I imagine that whatever compression gets the film to fit was used although anything above PAL speedup would probably be too conspicuous due to the pitch change.

If the video frames have been blended during the compression or perhaps some atypical pulldown pattern used you may be able to deduce the speedup by counting the number of discrete frames in a certain duration of time and working from that
Reply
Thanks given by: pipefan413
#3
(2020-10-26, 02:42 AM)zoidberg Wrote: I imagine that whatever compression gets the film to fit was used although anything above PAL speedup would probably be too conspicuous due to the pitch change.

If the video frames have been blended during the compression or perhaps some atypical pulldown pattern used  you may be able to deduce the speedup by counting the number of discrete frames in a certain duration of time and working from that

That's what I feared might be the case, aye: it might just depend on how long the film is. If the film's longer, it needs sped up more; if it's shorter, less speedup needed.

I'm not needing to actually keep the video for viewing purposes anyway, so it doesn't really matter if it looks like crap (in terms of running a really specific manual IVTC or whatever) but I get what you mean about frame counting to extrapolate how much difference there is. The less calculated but potentially easier way is probably just to try applying a few different resamples by trial and error until I get close, then fine tune it until it syncs well with the majority of my mono capture from the early Japanese LD transfer (almost certainly same source). I'm only using this for patches anyway, most likely.
Reply
Thanks given by:
#4
So, if I well understand, the Japanese LD with mono would be the main track, while the US time compressed one would be used for patches, right? Then, do you really need to stretch few milliseconds?
Also, if you can grab the VHS, then you could eventually use this instead of time compressed LD.
Sadly my projects are lost due to an HDD crash... Sad
Fundamental Collection | Vimeo channel | My blog
Reply
Thanks given by:
#5
(2020-10-26, 03:36 AM)spoRv Wrote: So, if I well understand, the Japanese LD with mono would be the main track, while the US time compressed one would be used for patches, right? Then, do you really need to stretch few milliseconds?
Also, if you can grab the VHS, then you could eventually use this instead of time compressed LD.

Well, one of the moments I might need to patch is quite a big hole in the sound and it has repetitive background music that would probably make it really obvious if it wasn't the right speed (it'd be audibly too fast for the patch then slow down when it cuts to the JP mono). So yeah.

The VHS is definitely on my wishlist, yes. Trouble is it would need to be one very very specific VHS, since most of them have the Dolby Stereo mix as far as I can tell. And it's probably the same source, so again, likely only useful for the side changes and not so much for the frames missing from the source print.

But yes, that's the idea: most of it is either the first or second issue Japanese LD mono, to be patched over with a combination of whichever elements prove most transparent. That may mean using a custom mono downmix (with noise floor from analogue mono mixed in) for the missing frames, but the time-compressed LD or alternative mono VHS for the LD side changes. I don't know until I hear everything and can assess how useful each source is. The time-compressed LD hasn't arrived yet and I haven't even bought the VHS yet because I've only found one copy and it's bloody expensive. (Also I don't know if I would need a TBC to capture VHS correctly, I've never tried a VHS capture before.)
Reply
Thanks given by:
#6
VHS capture: if you don't need video, using a very good player (recorder) probably you would not need a TBC to grab audio; but if you can pass through a DVD recorder (that has TBC) it is wise... and any HiFi Stereo VHS tape has also the mono track for compatibility reason; if this just a fold down version is out of my knowledge, though!
Sadly my projects are lost due to an HDD crash... Sad
Fundamental Collection | Vimeo channel | My blog
Reply
Thanks given by:
#7
(2020-10-26, 04:03 AM)spoRv Wrote: VHS capture: if you don't need video, using a very good player (recorder) probably you would not need a TBC to grab audio; but if you can pass through a DVD recorder (that has TBC) it is wise... and any HiFi Stereo VHS tape has also the mono track for compatibility reason; if this just a fold down version is out of my knowledge, though!

Aye, I've found the mono track - for instance on the first release of STAR WARS - to be from "mono compatible" Dolby Stereo tracks, for the most part. That said, I wouldn't be surprised if the very very first US (and possibly European e.g. UK) VHS release of THE EXORCIST probably does have the actual mono track as well. I've only really seen the anniversary / special editions, some of which are quite nice sets, but none of which have the mono. The oldest one I've found so far is only from 1991, has the Dolby Surround track, and even shares the same catalogue number as both the US LaserDisc (1993) and US DVD (1997, the double-sided one with 4:3 and 16:9) I already own!

Good point though, I probably don't need TBC for just grabbing audio. I have no idea, though, maybe my VCR has a TBC in it anyway. My guess would be that it probably doesn't, it doesn't strike me as particularly high end... it's one of my more memorable eBay purchases, because it arrived in a giant box with smelly old cushions as packing material instead of bubblewrap/polystyrene, with all the cables etc. jammed inside the slot (which made me rather angry but luckily hasn't damaged it) and a copy of THE GREAT ESCAPE left inside it, presumably forgotten for god knows how many years.
Reply
Thanks given by:


Possibly Related Threads…
Thread Author Replies Views Last Post
  Back to the Future Trilogy 4K Laserdisc PCM Syncs crampedmisfit1990 2 223 2020-11-10, 06:59 PM
Last Post: TheHutt
  Laserdisc PCM Rips Available HippieDalek 48 7,756 2020-10-15, 01:04 AM
Last Post: zoidberg
  Mortal Kombat Laserdisc Audio? alleycat 1 320 2020-07-21, 12:50 AM
Last Post: alinskey
  DTS soundtracks on laserdisc and not on DVD or BD? spoRv 6 2,807 2020-06-29, 09:25 PM
Last Post: BDgeek
  Mission: Impossible AC-3 LaserDisc borisanddoris 20 4,400 2020-06-15, 10:57 PM
Last Post: BDgeek
  RAIDERS OF THE LOST ARK LaserDisc audio gap(s) pipefan413 11 1,062 2020-06-09, 09:38 PM
Last Post: pipefan413
  Goonies laserdisc montagekid 1 409 2020-05-05, 11:43 AM
Last Post: Kynch
  Does anyone have a copy of Terminator 2 laserdisc's PCM? PDB 14 5,655 2020-02-22, 11:10 AM
Last Post: Stamper
  "A Charlie Brown Christmas" laserdisc audio, anyone have it? Dek Rollins 6 2,058 2019-12-16, 10:22 PM
Last Post: Dek Rollins
  Goonies Laserdisc PCM bronan 4 1,885 2019-09-06, 01:31 AM
Last Post: Chris Knight

Forum Jump:


Users browsing this thread: 1 Guest(s)