Linking Multiple 7-Series Recorders Using C. Link

Sound Devices 7-Series recorders are equipped with a proprietary C. Link (control link) 6-pin modular input and output connections. These connections allow multiple 702, 702T, 722, and 744T recorders to be daisy-chained together for recordings requiring high track counts. C. Link also provides a connection to the CL-1 Remote Control and Keyboard Interface. When linked, 7-Series recorders have a source/sync relationship. The source recorder and the sync device will share sample accurate start and stop record times. The C. Link protocol carries the following data:
  • word clock
  • time code information (702T, 744T only)
  • RS-232 serial data
The following tech note explains proper methods and limitations when multi-unit linking 7-Series recorders via C. Link.

How to Link Recorders

  1. Link multiple units using the Sound Devices XL-RJ accessory cable to connect the source recorder's C. Link Out port to the sync recorder's C. Link In port. Additional recorders can be connected in the same Out to In manner. See the above illustration. Linking is reliable for up to three recorders. If more than three recorders need to be linked, route WORD CLOCK OUT from the source device and first sync device to recorders four and five, respectively. The maximum number of linked recorders is five, and is independent of sampling rate. If more than three recorders are linked without routing WORD CLOCK, the amount of jitter will build up and files on downstream sync devices may experience recording drop outs.
  2. Power the source recorder first. Wait for this recorder to boot up completely, and then power the next recorder in the source/sync relationship, waiting for it to boot completely. Repeat this process until all recorders are powered up.
  3. Set all linked recorders to the same sampling rate, bit depth, file format, and time code frame rate (if used). This will ensure that all files generated between linked recorders are compatible.
  4. If time code is being used, set the sync devices in the Setup Menu option TimeCode: Mode to EXT TC. This will ensure that sync devices will follow the source recorder’s time code generator. Do not use the EXT TC - Auto Record mode as this will send two separate record commands to the sync recorders. Dependent on the user's setup in the Setup Menu option File: Marker Mode this could create two takes on the sync recorders for every one take commanded by the source recorder.
  5. Set scene names on each of the units for easy identification in post production. Take numbers should be the same on all linked recorders if the take numbers are reset before recording. There is no file name synchronization with multiple unit linking.

Things To Consider When Multi-Unit Linking:

  • When linked, record start and stop commands on sync devices will not affect “above” recorders in the linked chain. This makes it possible for take numbers between linked recorders to get out of synchronization. Commanding record and stop functions only from the source device will assure that all recorders begin and end recordings together.
  • When Using the CL-1 Remote Roll and Keyboard Interface with C. Linked units keep in mind that only record start and stop functions transfer to sync devices. All other CL-1 commands will only effect the source recorder.
  • The C. Link jack is a proprietary RS-232 port. Under no circumstances should analog or digital telephone lines be connected to either jack. Serious damage to the recorder could result.
  • Although the RS-232 standard allows for cable lengths of up to 50 feet, the recommended maximum length of C.Link cable between any given pair of 7-series recorders is 4 feet. Longer cables lengths introduce the risk of the sync device losing word clock synchronization with the source device.