Setting up Synchronization for a Postproduction Suite
In audio for video postproduction, you often need to synchronize with a 9-Pin VTR in order to work with video material. At the same time the audio clock has to be synchronized with the video clock source to ensure that both audio and video run at the same speed.
Finished audio can then be recorded back onto the digital audio tracks of a VTR in perfect sync with the video (known as layback). In this example, 9-Pin machine control is used. The audio clock is a word clock signal generated by the house sync generator that also generates the video sync signal. Timecode is handled by a SMPTE to MTC reader, such as the audio interface.
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The house sync generator creates both the video sync and audio word clock so that the VTR and Nuendo play at the same speed.
When laying back digital audio to the VTR, the AES signal will already be in sync with the VTR’s digital audio inputs.
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9-Pin machine control is used to manipulate the VTR’s transport.
The VTR can shuttle, locate, play, and record from commands issued by Nuendo. Also, Nuendo can arm audio tracks on the VTR for layback.
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When the VTR enters play, LTC is fed back to Nuendo which locks to that incoming timecode.
If the LTC reader is part of an audio card that is APP compatible, sample-accurate synchronization is possible in this scenario.
To lay back finished audio to the VTR, proceed as follows:
Procedure
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Make the connections as shown in the diagram.
Ensure that video sync and word clock are tied to the same generating source.
- Select .
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On the Sources page in the Timecode Source section activate ASIO Audio Device or MIDI Timecode.
Depending on your system’s configuration, the sound card might have an LTC reader built into it or you may have to use a LTC to MTC converter interface to get timecode into Nuendo.
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Open the Machine Control page, and in the Machine Control Output section, activate 9-Pin Control 1 or 9-Pin Control 2.
Nuendo’s transport buttons will send commands to the VTR over the 9-Pin RS422 connection.
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Select or .
Using the Auto Edit feature, you will be able to perform laybacks to the VTR via digital audio connections. VTRs with digital audio tracks use 48kHz as a standard sampling rate. Some decks only have 20 bit depth capacity so make sure to dither properly for the intended delivery format.
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Click Online.
Now you can use the device panel to control the VTR.
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Test the transport with the 9-Pin device panel.
Ensure that all connections are working properly by testing the various transport buttons on the panel.
- Record-enable the audio tracks that you want to record to.
Most professional VTRs have 4 audio tracks. Many high-definition VTRs have 8 for recording 6-channel surround sound plus a stereo downmix all on the same tape.
- Play back the project and look at the meters on the VTR to ensure that proper recording levels are set.
That way you can also make sure that the digital audio connections are working properly.
- Set the left and right locators to the punch in and punch out points.
Auto Edit uses the left and right locators to program the record in and out points of the VTR.
- Ensure that the pre-roll and post-roll times are appropriate for the VTR.
In most cases, the default values will be sufficient for the VTR to get up to speed before punching in.
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On Nuendo’s Transport panel, activate Sync.
This turns Nuendo into a timecode slave. Once the VTR starts to play, Nuendo will sync to incoming timecode.
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On the 9-Pin device panel, click Auto Edit.
This starts the Auto Edit process. The tape transport locates to the set pre-roll position (by default, 5 seconds before the left locator) and starts playback. When the left locator is reached, the VTR enters record mode.
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Auto Edit is complete when the right locator is reached and the VTR goes out of record.
After reaching the right locator, the VTR continues playing for the set post-roll time (by default 2 seconds) before it stops.