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Synchronization - however did we get involved with that crock of sh*t?

These days you are a great sound engineer if you understand synchronization. Whatever happened to being able to get a great recording and a great mix?


There are two aspects to synchronization. One is getting multiple machines to run at the same speed, at corresponding points in the recording. An example would be an audio recorder synchronized to video playback on VHS, or Digital Betacam if you work at the top of the industry.

Over the years a standard has emerged where the video machine will typically be the master and the audio recorder will synchronize to that. It works with analog multitrack tape, digital multitrack tape such as DTRS (still in common use) and disk recording systems such as Pro Tools. So basically anything audio needs to be able to synchronize to anything video.

But we started to move away from that. It became possible to digitize a video tape recording into a computer system, and display the images as a video track in the recording software. Any audio tracks recorded to this sequence of pictures would automatically be in synchronization. No longer was it necessary have a synchronizer to sync audio to picture - it just happened.

But at the same time, a new requirement for synchronization was emerging - digital audio devices need to be synchronized to other digital audio devices.

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Going back to analog, you can copy an analog recording from one machine to another. No synchronization required. But to copy a digital recording from one DAT (for example) recorder to another, the two DAT machines have to be synchronized.

The reason for this is that the sampling rates of the two machines have to be absolutely identical. This will not just happen by accident.

Fortunately, this is easy. The sync information is contained in the signal and the record machine will automatically synchronize to the playback machine.

But it only works with two machines. Set up a system that involves even one other digital device, a mixing console for example, and things become rapidly more complex.

Now, the only practical way to work is to have a master 'clock' source that supplies digital synchronization information to every machine in the entire system.

Professionals would use a dedicated clock generator and everything would synchronize to that. It is sometimes called 'house sync'.

Any digital recorder, mixing console or effects unit worthy of being called professional must have the ability to synchronize to house sync. If one item does not, then suddenly you are in the position of everything having to synchronize to that one rogue item.

I think you are getting the picture that the whole synchronization issue is a crock of sh*t.

Oddly enough, many people don't need to get involved to even the slightest degree. If you record music on a Pro Tools system, or any similar system that can record, mix, add effects and master all within the one software or hardware. Synchronization is never necessary.

If any sound sources connected to the system provide signal in the analog domain, then still no synchronization is necessary. It is only when you decide to incorporate another digital device that suddenly you become embroiled in all of this complexity.

My advice - steer well clear of anything involving synchronization unless absolutely necessary. If you can work in a strictly sync-free studio, then you will be massively more productive than anyone who has to get multiple machines to work together.

By David Mellor Sunday October 30, 2005