Applies to: 

All interfaces featuring Optical/ADAT ports

If you are having issues with your ADAT setup, including audio not coming through, clock not syncing, or clicks and pops in your recordings, see the troubleshooting steps below.

Verify Optical Connections

Are you using the correct cable?

Make sure you're using a TOSLINK (optical) cable, also known as fibre-optic or lightpipe:

Any of the following should work just fine for example:

• Amazon Basics TOSLINK Optical cable (Amazon)
• the sssnake Optical Cable (Thomann)
• Hosa OPT-102 Fiber Optic Cable (Sweetwater)

Is the optical cable connected correctly?

TOSLINK (optical) cables typically come with a small plastic cover to protect the tip of the cable; you need to remove this cover to fit the cable into the ADAT/Optical ports of your interface.

Once the plastic cover is removed, the TOSLINK connector should click into place when fully inserted into the optical port. If the shape of the housing surrounding the TOSLINK connector is too large, it might be preventing you from inserting the connector fully. In this case, try a cable with a smaller connector housing.

For reference, see: My TOSLINK ADAT cable doesn't fit into an ADAT port

Is the optical (ADAT) Output port passing signal?

Optical ports use light pulses to encode digital information. If you visually inspect an ADAT Output port on your audio interface or expansion unit, you should see a red light coming from that port. If you don't, perhaps the port is faulty. Note that the device in question needs to be powered on, and you may need to lift the flap protecting the port. There's no signal coming out of an Input port (i.e. no light).

Is the optical cable passing signal?

Like optical ports, optical cables use light pulses to encode digital information. If you connect an optical cable to a working ADAT Output port, you should see a red light coming out on the other end of the cable. If you don't, and there's a red light coming from that output port, perhaps the optical cable is faulty. If this is the case, try a different TOSLINK (optical) cable to rule out a faulty or damaged cable. 

Are your optical cables connected to the correct optical ports?

Inputs must be connected to outputs, and outputs to inputs. If your audio interface or expansion preamp has multiple ports, check the labelling of the ports or the user guide (Focusrite Downloads) to ensure you are using the correct ports for your configuration.

In the example below, the first ADAT (optical) Out port of the preamp/expansion unit (Clarett+ 8Pre, top) is connected to the first ADAT (optical) Input port of the audio interface (Scarlett 18i20 3rd Gen, bottom).

Likewise, the first ADAT (optical) Out port of the audio interface (Scarlett 18i20 3rd Gen, bottom) is connected to the first ADAT (optical) Input port of the preamp/expansion unit (Clarett+ 8Pre, top).

Verify Clock, Sync, and Sample Rate

Clock Source and Sync Settings

Clocking is required for devices to synchronise digital audio. Every device should follow the clock of the same device, the clock leader. You should set the leader's clock source to Internal, and set all other devices (followers) to follow the leader's clock to their connection (e.g. ADAT, S/PDIF, or Word Clock). 

Most of these digital formats are one-way connections. Therefore, it may be most practical for a preamp/expansion unit to be the clock leader — for example, if the only digital connection is from an ADAT output on an expansion preamp to an ADAT input on an audio interface.

Usually, you can select the clock source either via software (e.g. the control app for your audio interface):

Or directly on the hardware (e.g. dedicated buttons on the front panel of pre-amps/expansion units):

If one of your devices has no clock settings, check the user guide to see if it can automatically detect an incoming clock. If it can't, you probably have to make this device the clock leader.

For more information on clocking, see the following articles:

• Understanding Clocking
• What are the Clock Source and Sample Rate?
• What should my Sync/Clock Source be?

Sample Rate

Matching the sample rate on all devices is essential to digital clock synchronisation. All devices, as well as your recording application/DAW (if using one), must be set to the same sample rate. This is usually achieved either via software (e.g. the control app for your audio interface):

Or directly on the hardware (e.g. dedicated buttons on the front panel of pre-amps/expansion units):

Note that if using a DAW, the audio interface connected to your computer will sync its sample rate to the one set in your DAW project. 

As with clocking, if one of your devices has no sample rate settings, check the user guide to see if it can automatically detect sample rate changes. If it can't, you probably need to adjust the sample rate of the other devices to match the device in question.

For more information on sample rate, see the following articles:

• What are the Clock Source and Sample Rate?
• Sample Rate, Bit Depth & Buffer Size Explained
• How to Change Sample Rate & Buffer Size Settings on Windows

Verify Audio Connections

Is the gain dial for the channel turned up?

Turn the gain up as much as needed to produce sufficient signal. Some equipment may require maximum gain from the preamp/expansion unit. For reference, see the following articles:

• How high should I set the gain control on my interface?
• I have to set the gain on my interface high to get a good input level

Are you using the correct connectors and inputs?

Check that the inputs you are using accept the type of signal you are inputting, and ensure you are using the correct connectors — for example, some preamps only accept mic level via XLR, and instrument or line level via 6.35mm (¼") jack. For reference, see this article: What are the differences between mic, line, and instrument level?

XLR input

6.35mm (¼") input

Combo input (both)

Is 48V phantom power enabled if needed?

48V phantom power can damage equipment that is not designed to use it. Check with the manufacturer to confirm if the equipment requires 48V phantom power.

Mics, DI boxes and some other equipment can require 48V phantom power from your ADAT preamp/expansion unit. If required, engage the 48V phantom power switch on the preamp/expansion unit:

Please see this article for more information about what 48V phantom power is and how to use it: What is 48V phantom power?

Is instrument level enabled if needed?

For instrument-level signals (e.g electric guitars), check if there is an instrument-level setting that needs to be engaged on the preamp/expansion unit. This is generally referred to as Inst on Focusrite products, but is sometimes referred to as Hi-Z (high impedance) or simply indicated with an image of a guitar:

For reference, see this article: What are the differences between mic, line, and instrument level?

Have you tested another input?

Try connecting your microphone/instrument/line-level gear to another input on the same preamp/expansion unit to see if you have the same issue. This can highlight any incorrect settings or point to a potential fault with a specific channel. Note that the ADAT channel that receives that input signal on your interface will change. For example:

• Preamp/expansion unit Input 1 = audio interface ADAT 1
• Preamp/expansion unit Input 2 = audio interface ADAT 2
• Preamp/expansion unit Input 3 = audio interface ADAT 3

Have you tested a different audio cable?

Try different known working audio cables to rule out an issue with the original cable. 

Are you using the correct connectors and outputs?

Check that the inputs you are using accept the type of signal you are inputting, and ensure you are using the correct connectors. For example, some preamps only accept microphone level via XLR, and instrument or line level via 6.35mm (¼") jack.

For reference, see:  What are the differences between mic, line, and instrument level?

6.35mm (¼") output

XLR output

DB25

Are any other features enabled that should not be?

Your ADAT preamp/expansion unit may have an insert, filter or other feature enabled that is affecting the signal:

Check with the manufacturer if you aren't certain what a feature does — you can refer to the user guide for any Focusrite products: Focusrite Downloads.

Verify DAW and Software Routing

Are you selecting the correct input channels in your DAW?

If you are looking to record the incoming ADAT signals, note that the inputs on your interface vary depending on which inputs are available, what sample rate you are using, and what ADAT or S/PDIF mode you are in. For reference, see this article: Digital I/O Modes

You can check the input numbering (channel listing) for your current configuration in the user guide: Focusrite Downloads.

Have you routed the correct ADAT channels to the Line Outputs of your interface?

If you are looking to output the preamp/expansion unit's ADAT channels through your audio interface's Line Outputs, you may need to configure the routings in the control app for your interface. In the example below, this is illustrated for a Scarlett 18i20 4th Gen using Focusrite Control 2, where the Analogue Outputs (Line Outs 1-8) are set to pass the corresponding incoming ADAT channels (ADAT 1-8).

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