Creating a New Video Session

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Creating a New Video Session

Once all of your equipment has been connected and configured for video, it is time to create a new video Pro Tools session. Close any current session you might have open , unless you are already working with one that needs to be viewed with picture. Choose File > Create Session > New Session in order to open the New Session dialog box, shown in Figure 4.12.

Figure 4.12. The New Session dialog box in Pro Tools 6. It includes choices for file type, sample rate, bit depth, and I/O configuration.


Choosing Sample Rate and Bit Depth

The sample rate of almost any film, video, or multimedia audio should be 48k. If you're working in hi-resolution sample rates, then a multiple of 48k would be fine96k, perhaps. This way, any further conversion back to 48k later will be relatively painless. 44.1k is not a standard sample rate for video. However, there might be certain situations in which 44.1k would be the better choice for computer-based multimedia workcertain media creation applications might prefer a 44.1k source file for audio. Be sure to discuss this with the content creators during pre-production.

The bit depth choice is more complicated. You must weigh factors of speed and efficiency against audio quality and dynamics as they relate to the current project. For instance, if you were starting a film project that was very serene and you wanted the quietest noise floor possible, then 24 bit is the way to go. In fact, I would suggest that 24 bit is always the preferred bit depth unless speed is a higher priority. In cases in which you are working with OMF files from an Avid workstation, the source media will usually be 16 bit (though the latest high-end Avid systems will now support 24-bit audio). When converting 16 bit OMFI into Pro Tools sessions, it will take more time to convert them to 24-bit files. The same is true if you must return edited OMFI files back to the Avid or other video editor. Careful discussion of OMFI formats in pre-production can help prevent screw-ups and confusion in this regard.

Choosing Frame Rate and Frame Count

The choice of frame rate and frame count depends on the nature of your current project. Once again, choice of frame rate should be determined in pre-production. Typically, a video session will use 29.97fps SMPTE with or without a drop-frame count. If the video is in PAL/EBU format, then a frame rate of 25fps will be used. Film and 24p HD sessions can use 29.97 as well, but it might need to be pulled down in order to match the speed change of 2-3 transfer process. In some cases, a frame rate of 24fps will be used for projects that will end up on film in their final format.

Small-duration Internet media projects might not require a specific SMPTE format if they will not be using any tape format. Flash files do not use SMPTE time code as a reference.

Choosing Session Start Times

In the Session Setup window shown in Figure 4.13, you can alter the SMPTE start time of the current session. Pro Tools defaults to 00:00:00:00. Most videos will use 01:00:00:00 as a standard start time for program material. The reason for this is that certain test tones and countdown pre-rolls must be included prior to the start of the program. If a start time of 00:00:00:00 is used, then anything prior to that will have SMPTE times in the high numbers23:59:55:15, for example. When the actual program starts, SMPTE will pass through the "midnight hour " and go from 23:59:59:29 to 00:00:00:00. This transition has unpredictable results with many SMPTE readers. The use of 01:00:00:00 as a start time eliminates this unpredictability . However, it is not a good idea to set the Pro Tools session start time at 01:00:00:00 because you need to allow for some space before the program starts to allow for test tones and sync beeps, such as the standard 2-beep tone. This requires that the Pro Tools session start time be earlier than one hour. The actual material itself should start at one hour.

Figure 4.13. The Session Setup window. Here you can change the SMPTE start time of the current Pro Tools session, among other things.


NOTE

THE 2-BEEP SYNC TONE AND HOW TO CREATE ONE

The 2-beep is a standard way of synching audio tapes to video or film reels. A short 1kHz tone beeps exactly two seconds before the program material begins. These beeps can be used later to line up the audio with film or video. It is very easy to create a 2-beep in Pro Tools using the Audiosuite plug-in called Signal Generator. Set your grid value to :01 frame, then create a new mono audio track. Select a one-frame piece on that track starting at 00:59:58:00, then Open the Signal Generator plug-in and set the frequency to 1000Hz (1kHz) and the level to 20db. Hit the Process button and you now have a one-frame beep two seconds before the start of the program. Now someone else can use the sound of that beep to line up with the video frame that has the 2 countdown number in it, and your audio should run in sync with that video, assuming the clock (speed) reference is the same for both.

Two minutes before one hour, or 00:58:00;00, will work in most situations. This allows plenty of time to include calibration tones, 2-beeps, and slates (small recordings made of the engineer talking, giving information about the upcoming program, and pre-roll for tape decks). The typical procedure for video post-production facility is to start tape at 00:58:00;00, run color bars and a 1kHz reference tone from 00:58:30;00 to 00:59:30;00, and then begin a 10-second countdown at 00:59:50;00 to the program start at one hour.

It is possible to change the session start time in the Session Setup window later if you need to. When doing so, a dialog box will appear that asks you if you would like to maintain time code or maintain relative position, as shown in Figure 4.14. If you just want to increase the amount of time before the program starts, then choose the maintain time code option. Choosing the maintain relative position option will not create any more time before the first audio region.

Figure 4.14. The Change Session Start Time dialog box in Pro Tools.


The other reason for placing some time before your program in Pro Tools is to allow for the lockup time of external tape machines. No mechanical tape deck can sync up instantly; neither can Pro Tools, for that matter. Some pre-roll is needed to stabilize any synchronized system. This pre-roll should take place while no audio is playing. Pro Tools will not output any audio until stable sync has been established. Anywhere from two to ten seconds might be needed for pre-roll. There is an option for machine control that will allow you to define a pre-roll value in frames . Once this value is set for a particular tape machine, it should not need to be changed.

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PRO TOOLS R for video, film, and multimedia
PRO TOOLS R for video, film, and multimedia
ISBN: N/A
EAN: N/A
Year: 2003
Pages: 70

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