One particular production workflow that can be a sticking point for many projects is working in post with dual-system sound requiring synchronization.

Dual-System (aka Double-System) sound is simply that where the audio has been recorded separately from the picture, to a physically separate recording device and medium. The main unit used in the school for dual-system is the Marantz solid-state field recorder. This records 2 channel audio to compact flash memory cards in standard 48k 16bit.

This 48k 16bit recording spec is the same as most digital shooting formats that record audio in-camera such as DV and XDCAMEX. HDV is technically not 48k 16bit instead using Mpeg2 layerII audio which is compressed – somewhat like Mp3 – but it is very high bitrate compression – 192kbps. So whilst not perfect it is, for all intents and purposes, aurally lossless and when transcoded to the editing system is handled as 48k 16bit.

Assuming all other things being equal (mics, cables etc) the recording of audio separate from camera does not, of itself, provide for better quality audio but it does free the camera from being chained to a boom and cables. The key reason to separate camera and sound is to free up the movement of the camera and allow the camera operator to focus purely on the image and the sound recordist to remain focused solely on the sound. Dual-System sound is largely about division of labour along with physical constraint of the camera.

But before you reach for the field recorder and unplug the XLR cables from your camera there are some serious considerations you should take into account. Most significant is to be very mindful that the process of sync-ing sound and picture in post-production is a very tedious and highly time consuming task. Any production using dual-system sound needs to immediately account for a longer and more complex post-production path.

In this post I’ll outline some different contemporary techniques and processes for sync-ing sound and picture in post but there is an over-arching rule worth keeping in mind and considering…. Don’t record dual-system if you dont have to.

Lets face facts – so long as there’s no trade-off in quality (which there shouldn’t be using the same mic and cable in-camera as into field recorder) then recording audio to camera is, any way you slice it, WAY easier. All your audio is automatically in-sync and your post production time is cut in half. This of itself means you can spend more time making creative editing decisions rather than the tedious process of synching audio and video files.

There is a commonly held idea that dual-system sound is somehow by default ‘better’. But this isn’t necessarily true on a technical level. As above the standard 48k 16bit spec is the same on most digital cameras as it is on most field recorders.

If you have to move the camera on a jib or sometimes a dolly or on a steadicam or through a complex series of angles, or at a distance from the actors then of course unfettering the camera from the sound equipment makes sense. There’s also, as said before, a lot to be said for keeping the tasks of camera and sound crew separate.

But, in simple terms, whenever you can plug into the camera without effecting how the shot or scene is captured, then why wouldn’t you? Why wouldn’t you save yourself a heap of post time, which is extra time and money, resources that can be better spent elsewhere.

Similarly if you’re using radio mics it can often make sense on a small production to take these inputs directly into camera. Most cameras can have a wireless receiver strapped on without effecting the movement or operation of the camera itself. So why make life harder than it should be?

That said, syncing dual-system sound in post at some stage is inevitable so here are some contemporary digital methods you may choose to use on your next short film project. (i’ve also put this article in the Production Bible section for future reference)

Pre-Edit Sync and Transcode.
This method is the most laborious up front but it leaves the edit process itself largely free of any further technical wrangling. It’s also makes for a purely on-line process which is far more streamlined and direct but does require much more hard drive space for storage of lossless intermediate files.

The process is relatively simple but can be time consuming. Log and capture all your footage natively ensuring all clips are labeled correctly by scene, shot and take. Likewise you import all the audio takes similarly named.

- Place a video clip with slate mark on the timeline
- Place the corresponding audio take on the timeline
- Sync the two clips using the slate clap and audio spike
- Export the clip from the timeline as a new video file using a lossless intermediate format such as ProRes422 or Avid DNxHD (be sure to name the new sync’d clip by scene, shot and take)

These exported sync’d copies become your online edit staying unchanged in the same format right through edit, mix and grade, through to final encode.

A good way to employ this process is to lay out all your clips on a single timeline in your project and use timeline IN/OUT points, or the Work Area bar, to export individual sync’d clips as new files. This way if you ever need to fix a sync’d clip or return to the source files you can do so easily as a separate timeline in your project along side your actual edit.

Lossless formats such as ProRes and DNxHD export reasonably quickly because of the low amount of compression so whilst this process might seem laborious upfront it’s not really as time consuming as it sounds.

More importantly, whilst you do spend a lot of time upfront you gain a lot of time in the edit itself working with efficient, already sync’d, online files in a lossless 422 colour space.

The downside is you need big harddrives to house both the source files and the new Lossless intermediate files (which will 4x bigger than the source, approx 1gb/min for HD)

Cut first and Sync after.
This method is potentially very efficient initially but also can be very tedious. The idea is to edit a cut of your film first using just the temp audio recorded on-camera and sync your real audio on the timeline shot by shot once you have a cut of your film.

The advantage here is that when it comes time to sync you only need to sync up the clips you actually used and not waste time syncing shots you don’t need.

- Assemble your edit using the temp audio recorded on camera.
- When you have a cut of your film that is reasonably close to being in shape, space the shots out on the timeline to create working space ready for syncing.
- Add the audio clips to the timeline and sync each shot in your sequence (you will have to extend out the head of the clip to reveal the slate, synch the audio and then trim back place)
- When you have all the clips on the timeline sync’d up you can then reassemble your edit back into shape again, this time with the real audio.

If you’re going to use this method it pays to have a cuts-only edit which will make the clip by clip timeline syncing process easier. If you have a complex timeline it can be very tedious; potentially taking more time to unpack and repack your timeline clips than you saved by not syncing everything up front.

Nested Timeline Sync
This method has potential to be very flexible, allowing changes at any time, and efficient in not requiring rendering. It utilises the ability to nest timelines inside of a master timeline.

- Create a Sequence in your project named for the individual Scene/Shot/Take you are about to sync.
- Add the video clip to its sequence
- Add the corresponding audio to the sequence
- Sync the audio and video using the slate mark
- Close the sequence
- Create a new sequence for the next clip and repeat this process for all Scene/Shot/Takes.

This process will produce a set of ’sequences’ that are in fact individually sync’d clips.

From there you create another new Master Sequence which will become the actual edit. Instead of placing the raw Clips on to this new Master sequence timeline you edit with the sync’d mini sequences as discreet clips.

This method is fast, requires no exporting and allows for changes to be made to any sync’d clip at any time with automatic update in the Master sequence. The only caveat is that I have not tested this workflow with larger projects with lots of shots. I don’t know how Premiere and FCP will behave working with potential scores (if not a hundred+ Sequences). In ‘theory’ it should be fine….

Final Cut Pro Merged Clips
FCP offers another specialized method that is highly efficient and flexible. It provides a very similar workflow to the Sync and Transcode option above but without the need to export and create new files.

- Place a video clip into the Source Window and set an IN point on the clap mark.
- Do the same with the corresponding audio take setting an IN point on the clap mark.
- In the project bins select both the Video and Audio clips you just marked (click one them and hold down Command and Click the other)
- Go to the MODIFY menu and choose Merge Clips

This process creates a new virtual clip (much like a subclip) that combines the two together using the IN points for synchronization. You can then edit using the Merged clips as in place of the individual source clips.