Today’s Tech Tip is probably more recreational than helpful for most of us, but your inSync editor thought it was interesting enough to force on everyone. Following our recent WFTD entry, 2-pop, we received the following e-mail from a good Sweetwater customer who also happens to be the music editor for The Simpsons and Blast from the Past. Not only does it clarify the meaning and use of the 2-pop, but it also provides a lot of other interesting information about an industry most of us audio guys could stand to be more in tune with. So here it is, enjoy!
Here is an anal-retentive response to your recent WFTD entry about the “2-pop” which goes into boring detail and gives more clarity to some verrrry minor inaccuracies in the article.
You mention that the “2” is the last number on the “SMPTE” countdown banner. Well, not really. The countdown we are all so familiar with is actually called ACADEMY leader and counts down SECONDS from 8 down to 2 and the “invisible” 1 is in the black. There IS a SMPTE countdown that counts down FEET from 12 down to 3 (the “pop” is on 3) and an invisible 2 & 1 in the black. For the uninitiated, 35mm film runs at a speed of 3 feet for every 2 seconds (24 frames per second, 16 frames per foot) — so the Academy leader counts down seconds and the numbers appear every foot-and-a-half — the SMPTE leader counts down feet and the numbers appear every 2/3 second. BOTH are 12 feet (8 seconds) long.
Now, the “pop” serves two sync purposes. The one you mention at the end of the article regarding audio/visual sync is correct (although in a large theatre, it is difficult to be CERTAIN that the pop is in sync with the “2” just by watching the screen). But there is a more important sync issue served by the “pop”: the “pop” is usually cut into the main dialogue reel for dubbing. When a film reel is about to be “mixed” (or “dubbed”) this one “pop” is routed through the mixing console to ALL the master recording tracks (i.e. all the music tracks, dialogue tracks, effects & foley tracks, ADR tracks, etc.) so that the “pop” lands at that specific frame across ALL the masters. This way, when all the individual sub-masters (called “stems” in TV/Film biz) are later played back to be mixed down to the final print master, we will hear only one “pop” (even though there are dozens of them coming through at once). If we hear any “flamming” or “delay” or any anomaly in the “pop”, then we know one of the stems is out of sync. By the way, there is also a “pop” exactly 2 seconds (how many feet? this is a quiz, you know!) after the last frame of the reel for the same purpose. We want to only hear one “pop” at the END of the reel during print mastering to know that the reel STAYED in sync (no drift) during the running of the reel.
Lastly, you are right to say that the “1” is in the black so that we don’t see a number just before the start of the picture. However, you can’t “cue up” film in a projector at the “1” and have any prayer of it being fully “up to speed” within 16 frames before the first frame of picture. This takes me to a slightly new area — changeovers.
Ever notice the white circle in the upper-right corner of the screen every 15-20 minutes or so? There are 2 of them, 11 feet apart. Before multiplexes were all the rage, films would be screened using 2 projectors. The movie was broken down into 4 or 5 or 6 two thousand-foot reels. Projector “A” would do the ODD reels, Projector “B” the evens. The projectionist would start the movie on “A” and have the next reel threaded and standing by on “B” with the “8” of the ACADEMY leader in the gate. About 2000 feet (approx. 22 minutes) later, the first little white circle or dot would flash in the upper-right hand corner of the screen EXACTLY 12 feet (8 seconds) from the end of that reel. At that moment, the projectionist would start Projector “B” turning, but had a DOUSER in front of the lens to keep the light from shining through. Otherwise, you’d see the countdown superimposed on the end of the outgoing reel. Then, 11 feet later, the second white circle or dot appears and this signals the projectionist to lift the douser, allowing the light through. IF he/she has timed this correctly, we’re in the BLACK of the last foot of academy leader and still no light goes through thus not interfering with the last foot of the outgoing reel. Finally, the last frame of the reel on Projector “A” finishes at the same time that the first frame of the reel on Projector “B” goes through the gate and the movie continues uninterrupted.
Naturally, this is not an exact science as I’m sure many have noticed over the years. There is a human error factor to be considered; therefore “mechanical” changeovers are not precise. In multiplexes today, the ENTIRE film is joined into one giant reel (12,000-20,000 feet!) and played from a platter in a continuous loop not unlike an old 8-track cartridge. This eliminates the human timing issues of changeovers, but it’s still not perfect as the film must be broken down into 2,000 foot reels for shipping, then assembled in the projection booth. Over time, this constant splicing and breaking down takes its toll on the print, causing the changeover point to have many scratches, gouges, even lost frames. Home video on VHS and DVD have no changeover issues because the film is “assembled” in a computer for output and the changeover is perfectly smooth every time. I recently saw the digital screening version of “Toy Story” and there were no changeovers. The entire movie played from hard disc in a single pass. Kinda like watching in a huge home theatre! OK, that’s enough rambling for now.