4. The third film frame is transferred to the second field of video frame three and the first field of video frame four.

This is a block diagram of the 2-3 pull-down process. Notice that 4 frames of film are transferred to 5 frames of video using the 2-3 field technique.

5. The remaining film frames are transferred in this manner, alternating between 2 and 3 fields of video, until the end of the transfer.

After four frames of film have been transferred this way, an even five video frames will be created. Over the course of one second, 24 frames of film and 30 frames of video will have gone by. Since they are running at -0.1%, the actual frame rate is 29.97 video frames per second, the NTSC standard.

It is important to have a clear understanding of 2-3 pulldown in order to make accurate decisions regarding audio pull-down and video pull-up when working with NTSC film transfers in Nuendo. Film speed is faster than NTSC video speed.

When the audio is pulled down, it allows production audio (DAT tapes or files from a field recorder) from a film shoot to play in sync with NTSC video. Even though 29.97 fps is a faster frame rate than 24 fps (film speed), the video is running -0.1% slower than the original film due to the 2-3 transfer process and hence the need to slow the audio down a bit.

Many video editors working with NTSC video refer to 30 fps as “film speed” as opposed to 24 fps. The reason for this is if you speed NTSC video (29.97 fps) up by 0.1%, you are running at the same speed as the original film at 24 fps. Conversations regarding this can often get very confusing. Make sure you have a clear understanding of the material you are working with when dealing with film transfers and frame rates. It will avoid many mistakes and save time in the long run.

Compensating for film transfers to video

When working with film transfers to video, it is necessary to compensate for the change in speed that results from the telecine process. With Nuendo, there are two basic ways this can be done. The first is by adjusting the playback speed of the audio to match the speed of the video. The second is to adjust the speed of the video file to match the original speed of the film and production audio in Nuendo.

Adjusting audio playback speed

When adjusting audio playback speed to match the video, there are two scenarios based on the two video formats that film is transferred to, NTSC and PAL/SECAM. Since the telecine process for each video format results in different speed changes, there are two types of playback adjustments possible. For NTSC, the speed change is down -0.1%. For PAL/SECAM, the change is up +4.1667%.

Audio pull-down -0.1% (NTSC)

When working on a film project that has been transferred to NTSC video, most audio engineers prefer to use the original source tapes from the film shoot in order to retain the highest quality and fidelity. Audio that has been transferred to the videotape during the film transfer has suffered a generation loss and speed change.

Since the video is running -0.1% slower than the original film, the audio must also be slowed down by the same amount as the film in order to remain in sync.

To slow down audio playback in Nuendo, an external sample clock source will be needed to “pull” the clock speed down by 0.1%.

Your audio card must be set to external sync and connected to the clock device via Word Clock, VST System Link or some other clocking method for this to work.

Since the video and audio playback speeds are independent in Nuendo, the video will remain at the same speed while the audio is slowed down (pulled down). This will ensure that the production audio and film transfer will remain in sync.

You may receive an OMF, AES 31 or OpenTL file that contains audio from the original source tapes conformed to the edited video or you may have to record the source tapes into Nuendo yourself. Either way, you have audio in Nuendo that is edited to the picture but will not stay in sync with the video unless you pull down the sample rate.

When you are running at a non-standard sample rate (47.952 kHz = 48 kHz pull-down), digital transfers into Nuendo from external equipment must be made with the external equipment locked to the same sample clock as your audio card. Most devices are capable of a 0.1% change in sample rate and will function normally.

Any audio mixdowns that are exported from Nuendo when the sample clock is pulled down, will play back in other applications and devices faster since that sample clock will be running at the standard 48 kHz.

The idea is that when you have completed the audio mix for your film project, the video will be sped back up to film speed for the final transfer back to film and your audio mix can then be played at the standard 48 kHz sample rate (no pull-down) and will remain in sync with the picture.

Using this method preserves the quality of the original audio recording made during filming and allows for a digital mixdown transfer at film speed without any generation loss or sample rate conversion.

Audio Pull-up +4.1667% (PAL/SECAM)

Audio pull-up (+4.1667%) is the same concept applied to PAL/SECAM video transfers. Since the film is sped up by 4.1667% during transfer, audio in Nuendo must be running at +4.1667% speed in order to remain in sync with the video during editing and mixing.

In this case, the external clock must be set to +4% varispeed.

Devices such as the Rosendahl Nanosync are capable of varispeed and have presets for the 4.1667% necessary with PAL film transfers and the -0.1% for NTSC.

Once the project is complete, Nuendo’s sample clock can be returned to normal (48 kHz) for the final mixdown at film speed. Once again, this allows for a digital transfer of the final master at the correct speed for theatrical presentation.

Non-standard audio pulls

It is also possible to use pulled sample rates that do not fit one of the above scenarios. These sample rates would only need to be used in exceptional circumstances when an error has occurred elsewhere in the process of making a film. These settings could be used to correct for sync errors made at another studio or problems with video editing systems. Just about anything is possible.

• -4% Pull-down

If a film project was transferred to PAL/SECAM video and the audio editing and mixing was performed at video speed (48 kHz) without using audio pull-up, the final mix would be running at video speed not film speed. In this case a -4% pull-down could be used to correct this and get the audio running at film speed again. The downside to this is that the final transfer to film would have to either be analog or through a sample rate converter in order to be recorded with the film.

• +0.1% Pull-up

This pull-up is not normally used except in situations similar to the one described above but for NTSC video. It could be used to correct the speed of a project finished at video speed (without pull-down) prior to transferring it to film. Since film is moving 0.1% faster than NTSC video, the audio mix could be sped up to film speed using +0.1% pull-up for the transfer.

• Other pull-up/pull-down options

There may be other scenarios where non-standard pull-ups and pulldowns can be used to correct mistakes. Nuendo provides further pull- up/pull-down options for such situations in the Project Setup dialog and the respective section in the Project Synchronization dialog (see below).

All the examples used here are with 48 kHz as the standard sample rate for the film and video industry. However, it is possible to accomplish the same tasks using 44.1 kHz, 88.2 kHz, 96 kHz (this is double the standard sample rate and commonly used for higher fidelity), 176.4 kHz and 192 kHz, provided you have an external clock device capable of pulling these higher sample rates.

Timeline adjustments when using pull-ups or pull-downs

When the audio clock of your audio card is being slowed down or sped up from an external clock source, Nuendo has no idea that it is running slower or faster than normal. The time displays (minutes:seconds, timecode) will become inaccurate since they are based on a sample count, not the independent clock source.

Nuendo provides an adjustment of the timeline to compensate for these changes. This setting is found in the Project Setup dialog:

The Pull-up/Pull-down pop-up menu in the Project Setup dialog.

Whenever you apply an audio pull to Nuendo from an external clock, you should also set this menu to the appropriate choice. This allows Nuendo to recalculate the sample count to reflect the adjusted sample rate.

For example, if the setting is switched from no pull-down to -0.1% pull-down, events in the timeline will appear longer since the sample rate has been slowed down. The event display will show the accurate length of events relative to timecode, minutes and seconds. The project setup info line at the bottom of the Nuendo Track list will also indicate whether pull-up or pull-down is applied to this project.

Moving events

When you change the setting in the Pull-up/Pull-down pop-up menu and there are events already in the timeline, Nuendo prompts you to choose whether or not to keep the original sample start times or not.

•Selecting “No” allows events to follow the timecode and minutes:seconds clock change and remain at their SMPTE start times.

•Selecting “Yes” forces Nuendo to leave events at the same sample start time regardless of the clock speed change.

Video Pull-up and Pull-down

Nuendo also provides a method to adjust for film transfers by speeding up or slowing down playback of the video files in your project. Depending on the situation, it can be helpful to make the video file playback at film speed and not adjust the audio playback at all.

Adjusting the video playback speed back to film reverses the process used when adjusting audio playback speed. For NTSC video, the video playback speed must be adjusted up +0.1% back to film speed.

Nuendo does not offer a video pull-down for PAL/ SECAM since the -4% speed change necessary exceeds the video player’s capacity for varispeed.

Altering the video playback speed is done in the Device Setup dialog (Video Player page). You have two options: 0.1% pull-up and 0.1% pull-down.