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Author Topic: ID Frames and their effect on Sound Michael Brown Phenomenal Film Handler Posts: 1522 From: Bradford, England Registered: May 2001 posted 01-31-2003 06:23 PM                     From 'The Recruit' in Feature Info. quote: Brad Miller Wrote: Chop away ID frames between reel 2 and 3 and you will have a jump in the analog audio playback. Why only the analog track?  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 01-31-2003 06:39 PM                     Frequently 2 missing frames will not be noticeable when playing in digital, dts especially due to their crossfade. However since the digital audio is not recorded directly alongside the analog track, it would take some calculation to figure out if cutting them would create a noticeable jump or not. Just looking at the analog soundtrack and seeing the waveform go from very loud to almost nothing is easy to see.  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 01-31-2003 06:41 PM                        Of course, if you don't know how to properly make a splice the gigantic pop will distract the audience from the lost audio.  |  IP: Logged Michael Brown Phenomenal Film Handler Posts: 1522 From: Bradford, England Registered: May 2001 posted 02-01-2003 05:16 AM                     quote: However since the digital audio is not recorded directly alongside the analog track Oh, is digital not recorded 22 frames ahead of the image like the analog track?  |  IP: Logged Leo Enticknap Film God Posts: 7474 From: Loma Linda, CA Registered: Jul 2000 posted 02-01-2003 12:15 PM                        No. I don't know the offsets from memory, but it's a long way ahead. The delay is set manually, in numbers of perforations, on the processor. That way gives you flexibility as to where in the film path you position the reproducer.  |  IP: Logged Stephen Furley Film God Posts: 3059 From: Coulsdon, Croydon, England Registered: May 2002 posted 02-01-2003 12:44 PM                     Dolby Digital is printed 26 frames in advance of picture, I can't remember the others.  |  IP: Logged Michael Brown Phenomenal Film Handler Posts: 1522 From: Bradford, England Registered: May 2001 posted 02-01-2003 04:17 PM                     Wouldn't it make more sense to have the same offset for all the soundtracks? And why did they choose 22 for analog as opposed to 24?  |  IP: Logged Jeffry L. Johnson Jedi Master Film Handler Posts: 809 From: Cleveland, Ohio, USA Registered: Apr 2000 posted 02-01-2003 06:39 PM                        Read the threads "Digital Offsets" and "Audio Offset Documents" in this forum. 35mm analog is 21 frames ahead of picture. CDS is offset zero frames. Dolby Digital is 26 frames ahead of picture. DTS is offset zero frames. SDDS P side is offset zero frames. SDDS S side is 17 frames behind picture.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 02-01-2003 06:53 PM                    Dolby was smart because even though they started with penthouse playback they anticipated their system would lend itself to basement readers that retrofit existing soundheads so they went with an advance offset. 26 frames rather than 20 or 22 gave them a bit of flexibility in how such equipment would be designed. BTW, what sort of big jump in audio in The Recruit will there be with the aforementioned two frames removed and what's in that 1/12 second of audio that somehow makes it less jarring? Would it not qualify as fair use for scientific research to digitize a couple seconds on either side of the join then edit 1/24 second out on both sides to illustrate the difference with and without ID frames?  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 02-01-2003 07:05 PM                     It goes from almost silence to very loud. (I may have that backwards.) The buildup is over those 2 frames that most people have removed. It would be like snipping the beginning part of a song or word of dialogue. It would be noticeable. Had I had my digital camera with me, I would've taken a pic.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 02-01-2003 11:03 PM                    Well, I'm not saying you're wrong but I think it's pretty hard to judge by looking what the result of the snips would be. Tracks often go from very quiet to very loud. It depends on what exactly is in those two 1/24 second bits whether it matters at all. Either cut or uncut it's still going to be a big jump in level almost instantly and one presumes it makes sense in context. The lost frames certainly cannot be containing a gradual buildup. So how much of a difference they make remains an open question. Maybe they are important and maybe they are not. The visual evidence that a big change in level takes place there does not in itself prove the importance of the two frames worth of track.  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 02-01-2003 11:38 PM                     quote: The visual evidence that a big change in level takes place there does not in itself prove the importance of the two frames worth of track. Yes it does! Anyone who has ever edited audio and viewed the waveform can understand why it would have a jump/chopped sound. All it takes is 1/24 of a second for a jump to not sound right. Cut that down to 1/12 of a second and if the audio happens to be at the beginning or end of a word, or even just on the strike of a drumbeat in music...and it's obvious. As an example, if you were to record the sound of your voice saying "WHAT???" in a quick, stern tone and then went back and chopped out 2 frames worth at the beginning or end of it, you would hear it. Anyone would hear it.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 02-02-2003 10:50 AM                    Yes I agree but you cannot know if that is the case simply by looking. You're giving an example of where it makes a difference and I can give you all sorts of examples of sounds where a 1/12 second loss won't matter. What if it's a scene with quiet room tone up until an alarm clock goes off or a phone rings or there is a car honking outside? What if the sound change corresponds to a scene change 22 frames up in picture, going from quiet indoors to loud street scene? And on and on, ad infinitum. The point is not that you are wrong because you might be right. The point is that you cannot know just by looking.  |  IP: Logged Michael Brown Phenomenal Film Handler Posts: 1522 From: Bradford, England Registered: May 2001 posted 02-02-2003 10:55 AM                     I think that Brad means that the 2 frames contain the fade up.  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 02-02-2003 11:20 AM                     Yes that is what I am trying to explain, Michael. Without the 1 or 2 frame "fade up" of the sound, it would have a chopped effect to it. Go find a waveform of a car honking and lay it into a non-linear editor. Now edit out the first frame or two of the point where the honk starts. It would be obvious to anyone that something is missing or "skipped".  |  IP: Logged

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