TECHNICAL LIBRARY     References & Synchronisation

Ensuring all the machines are running at the same speed is a fundamental to all recording sessions. Where at all possible we lock tape machines, digital recorders and video decks to our house video reference. This results in all machines locking to the same video frame edge. Failing this (or where situations dictate) we use wordclock or AES. Internal references are very rarely used.

At AIR Studios we run a pair of Trilogy Mentor digital SPGs (Sync Pulse Generators). They are configured as master and slave, the master providing the ultimate 10MHz clock from which all references are derived. This enables us to provide 25fps (PAL), 29.97fps (NTSC) & true 30fps (Black & White) black & burst video references, as well as 44.1KHz & 48KHz wordclock & AES references. Since they all have a common master clock we can run ANY combination with no drifting, e.g. PAL and NTSC on the same session if required. All signals are distributed via Pro-Bel distribution amplifiers throughout the studio.

The studios use Timeline Lynx synchroniser modules. We rate these as the worlds most accurate and reliable units for all tape synchronisation. A comprehensive film session in Lyndhurst Hall could be running the following:

Two 24 Track Analogue 2" each resolved to NTCS reference with Lynx II modules.
Sony 334848 Track DASH digital tape with NTSC ref and lock & release with Lynx II.
Protools HD (96K) with SYNC I/O referenced NTSC and chasing master code.
Protools MIX with USD referenced to NTSC, chasing code, playing Quicktime movie.
Sony NTSC BetaSP or 3/4" Umatic as back-up picture with Lynx II module.
PAL 3/4" Umatic recording Conductor Cam for playback during overdubs.

All Lynx modules are under the command of a Lynx SSU (System Supervisor Unit) additionally providing "perfect timecode" for the Protools, DATs, Neve Encore automation & anything else that needs it. The Assistant Engineer has a single point of control with the Lynx KCU (Keyboard Control Unit). From the KCU he or she can select which machine is the master, which are online, set tape machines "wild" (critical when recording code).

Studio 1 also features a Timeline KCU for remote control. Studio 2 has a Motionworker V5 and remote integrated with the SSL. The Dubbing Suites all have AMS-Neve MCS (Machine Control Systems) integrated with the Audiofile hard disk recorders, providing synchronisation multiple 9-pin.

Issues

Analogue tape machines MUST be resolved and locked to a video reference if you wish to transfer audio to and from a hard disk system such as Protools. The hard disk system must also have the same reference signal. If the audio on the tape machine starts in time with the hard disk, then drifts out over time, check all machines are correctly referenced. However if it was recorded without a common reference the only chance of sync is to re-use the same equipment used at the time of transfer and hope for the best.

When striping analogue tape it's synchroniser MUST be offline or "wild". The code track will be on input when you record. An online the synchroniser will attempt to resolve the machine to the code. This will result in, possibly huge, speed variations on the tape deck.

Protools MIX systems will not varispeed above 50KHz even though the software claims to be running faster. This is the maximum speed the converters will run and if the session is at 48KHz this is just +4%, less than a semitone (6%).

Protools HD under OS9 does not lock sessions to the same video frame on successive passes unless you run 5.3.1cs7. This issue will render transfers to analogue tape useless. See digidesign's release notes on cs7 for more information. AIR Studio technical team were responsible for finding and diagnosing this issue.

Technical Library