Before setting the clock source of one or multiple Symphony I/Os, connect clock cables as described in Making Hardware Clock Connections.
If two or more Symphony I/Os are included in the system, select one unit as the Loop Master in the Maestro System Settings tab window. In most cases, select the first unit connected to Port 1 of the Symphony 64 Thunderbridge or PCIe card or Pro Tools HD Core card (or Port 1 of the 1st HDX or HD Native card).
When configuring your Symphony I/O system, first set the clock source then, depending on the setting, set the sample rate. Depending on the audio interface mode, the clock source/sample rate may be set from Symphony I/Oʼs front panel, from Maestroʼs System Setup tab, or from Audio MIDI Setup. See specific instructions for each audio interface mode below.
To set clock source from Symphony I/Oʼs front panel:
- Press and hold the left hand encoder until the current clock source is shown on the OLED Display.
- Turn the left hand encoder to select the desired clock source.
- When selecting Digital, turn the right hand encoder to select the specific digital input to be used as the clock source.
- Click either encoder to confirm the new clock source selection.
To set clock source from Maestro software.
- Click the System Setup tab
- Choose the desired entry in the Clock Source drop down menu.
To set clock source in Audio MIDI Setup:
- Choose Window Show Audio Window if the Audio Devices list isnʼt visible.
- Click on Symphony 64 in the left hand devices list.
- Select the desired source in the Clock Source drop down menu.
When audio interface mode is set to USB Audio, Symphony I/O operates only from its Internal clock. Thus, no Clock Source drop down is present in Maestro's System Setup tab in USB Audio interface mode.
To set clock source from Symphony I/Oʼs front panel:
- Press and hold the left hand encoder until the current clock source is shown on the OLED Display.
- Turn the left hand encoder to select the desired clock source.
- When selecting Digital, turn the right hand encoder to select the specific digital input to be used as the clock source.
- Click either encoder to confirm the new clock source selection.
To set clock source from Maestro software.
- Click the System Setup tab
- Choose the desired entry in the Clock Source drop down menu.
Clock source and sample rate are set in Pro Tools software and transmitted to Symphony I/O via the PC-32 (or DigiLink) connection. In Pro Tools HD audio interface mode, it's not possible to set clock source or sample rate from Maestro or from Symphony I/O's front panel.
In Pro Tools, choose Setup Hardware (Clock Source may also be set from Setup Session when a Pro Tools session is open). In the Clock Source drop down menu, select the desired source:
- To lock Symphony I/O to its Internal Clock Source, select Internal in Pro Tools' Clock Source drop down menu. If a single Symphony I/O is detected as 2 HD I/Os, either HD I/O drop down menu may be used.
- To lock Symphony I/O to its Word Clock Input, select Word Clock (sample rate) in Pro Tools' Clock Source drop down menu, where sample rate equals the actual rate of the session. When the session is running at sample rates of 88.2-192kHz, a second word clock entry at the base rate of 44.1-48kHz is found in the Clock Source menu - this is not a valid selection.
- To lock Symphony I/O to a Digital Input, please consult the charts below that indicate valid Pro Tools software clock sources according to the I/O Module(s) installed in your Symphony I/O. To avoid the complicated correspondance between Pro Tools Software Clock selections and Symphony I/O Hardware Clock Inputs, it's suggested to lock Symphony I/O to Internal or Word Clock!
8 Analog I/O + 8 AES I/O
8 Analog I/O + 8 Optical I/O
Note that Optical inputs and outputs (including the Opt In 1 ADAT clock setting) are not available at 176.4-192k sampling rates. 
16 Analog In + 16 Analog Out
16 Analog In + 16 Optical Out
Note that IO Module Optical Out paths are shown as Analog paths in Pro Tools. Though this does not affect the transmission of digital audio, Delay Compensation values added by Pro Tools to channels using these outputs won't be accurate. 
16 Optical In + 16 Analog Out
Note that IO Module Optical In paths are shown as Analog paths in Pro Tools. Though this does not affect the transmission of digital audio, Delay Compensation values added by Pro Tools to channels using these inputs won't be accurate. 