---
title: Symphony I/O MkII Multi-UNIT tips, tricks and troubleshooting
description: Here are some things to know about how the Symphony I/O MkII works in current Multi-Unit environments and with Control 2 in particular.
---
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# Symphony I/O MkII Multi-UNIT tips, tricks and troubleshooting
## Here are some things to know about how the Symphony I/O MkII works in current Multi-Unit environments and with Control 2 in particular.
#### What is different in Control 2 compared to Symphony Control
Unlike *Symphony Control*, channels in **Control 2** cannot be renamed.
Unlike *Symphony Control*, a **Control 2** Snapshot won’t store BOTH Symphony I/O Mkll’s in a multi-unit setup. You have to create a Snapshot for each unit.
#### Control 2 and Multi-Unit behavior
In a Multi-UNIT setup, unlike *Symphony Control*, **Control 2** does not "see" the two units as a single device. However, in Control 2 you can easily view either UNIT by utilizing the **Device** dropdown menu in the System Settings sidebar.
#### How to connect two Symphony I/O MkII's
With both UNITs disconnected from your Mac, make sure that UNIT A's CLOCK SOURCE is set to **INTERNAL** and UNIT B's CLOCK SOURCE is set to **WORD CLOCK**. Note: you MUST have a BNC cable going from the WORD CLOCK output of UNIT A to the WORD CLOCK input of UNIT B.
Next, connect the two UNITS to each other with a Thunderbolt cable. It does not matter which Thunderbolt ports you use. Finally, connect UNIT A to your Mac via a second Thunderbolt cable.
Boot Control 2 and confirm that it sees both UNITs.
**Sometimes**, If you hot-plug (daisy-chain) a ***second*** Symphony I/O Mkll to a Symphony I/O Mkll that is already connected to a Mac, you may have to restart the Mac. While both units may be recognized by Control 2, the second UNIT might NOT be recognized by Core Audio (or your DAW) until the Mac is restarted.
Note that when the units are seeing each other properly the front panel displays will show (in the upper right hand corner), one unit as **Master** **Unit: A** and the other as **Unit:B**. However, the status won't be displayed until one unit (A) is connect to a Mac.
This is what you will see in *Audio MIDI* when two Symphony I/O Mkll's are recognized by AudioMIDI (Core Audio). Each device is seen as a "separate Stream", but is automatically aggregated and is recognized by Core Audio and your DAW as a **single device**. In this case as **Symphony I/O MkII Thunderbolt** with a total of 72 inputs and 68 outputs. The number of inputs and outputs you see depends on which I/O modules are installed.
Also double check that your Symphony I/O's have the correct Clock Settings within Control 2. INTERNAL for UNIT A and WORD CLOCK for UNIT B
Usually, the two units will be recognized and UNIT A will set itself to INTERNAL clock and UNIT B will set itself to WORD CLOCK. However, you may encounter a situation where UNIT B's clock setting will flash (on the front panel) and the connection indicator in the upper right hand corner of the front panel will remain ORANGE. In this situation, disconnect the Thunderbolt connection to the Mac and use the front panel, to manually set UNIT A to INTERNAL and UNIT B to WORD CLOCK. Then re-connect the Thunderbolt to the Mac.
**How speaker outputs work in multi unit mode**
When two Symphony I/O MkII’s are daisy chained, UNIT A can have its analog outputs set to be either LINE or SPEAKER. However, the analog outputs on UNIT B can theoretically *only* be LINE level. When you switch between the A and B units in the System Settings sidebar in Control 2 you will see that UNIT B does not have “Analog Output Setup” or “Monitor Workflows” buttons.
#### If channel numbers are wrong in Control 2
Sometimes when two Symphony I/O Mkll’s are daisy chained, the channel numbers may be labeled incorrectly in Control 2. Or if you swap which UNIT is A and which UNIT is B - Or if after using a Symphony I/O Mkll in a two-unit setup, you want to just use a single unit - its channel labels may be wrong in Control 2. To fix this:
**Have a look at [this article](https://knowledge.apogeedigital.com/when-two-symphony-i/o-mklls-are-daisy-chained-channel-numbers-may-be-wrong-in-control-2?hsLang=en)**
#### Rare, but can happen
In certain circumstances, when in a Multi-Unit setup, you may see one or two Speaker Outputs on the first and second outputs of UNIT B as seen below. In theory, this shouldn't happen, but *sometimes* the 2 units can get confused, usually after changing the UNIT A / UNIT B Thunderbolt order.
If this happens, you may not be able to use the first two outputs of UNIT B. This can be fixed ***If*** you have a *known good* Snapshot of your UNIT B device that had been set to all LINE OUTS - you can load that Snapshot and the Speaker Outputs will change back to LINE OUTS. But, if you don't have a Snapshot for UNIT B , the guaranteed way to fix this is as follows:
Turn the Symphony I/O MkII’s OFF.
Unplug the Thunderbolt cables from your Symphony I/O MkII's and your Mac.
In your Macintosh HD, go to **/Library/Application Support/Apogee/Settings**
There you will see 1 or 2 files that begin with “**SIO2T-**” followed by a string of numbers and letters, and ending in **.xml -** DELETE these files (you will be asked for your password) and empty your trash. This is 100% safe.
Restart your computer.
Next, do a hardware reset of both units:
With all Thunderbolt cables disconnected, hold down the encoder knob on the front panel. Press the power button - and keep holding the encoder knob down until you see the main user interface screen come on, and then release the knob. Then repeat this process on UNIT B. Make sure that UNIT A's CLOCK SOURCE is set to **INTERNAL** and UNIT B's CLOCK SOURCE is set to **WORD CLOCK**. Note: you MUST have a BNC cable going from the Word Clock output of UNIT A to the Word Clock input of UNIT B.
With all of that done, reconnect the Thunderbolt cables in the desired order. First connect the two UNITS to each other with a Thunderbolt cable. It does not matter which Thunderbolt ports you use. Next, decide which UNIT you want to be UNIT A, and connect that UNIT to your Mac.
Boot Control 2 and everything should be back to normal.
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