Not getting any signal into your Apollo interface? If you don't see any signal registering on the front panel input meters of your Apollo, the problem may be related to how you're connecting your input device and how you have the Apollo's corresponding input configured. See below for an explanation of the physical input connections on Apollo interfaces and how to configure the Apollo for each input type.
Connecting via XLR
When connecting via XLR you will always need to set the corresponding Apollo input to "MIC". When a particular input on an Apollo interface is set to MIC the Apollo takes signal from the XLR connection corresponding to that channel. If you have your input set to MIC but are connecting via 1/4" TRS, or if you have your input set to LINE but are connecting via XLR, that would cause no input to show on the Apollo.
The image below shows two Console input channels set to MIC in order to accept signal from the XLR connections:
Connecting via 1/4" TRS
When connecting via 1/4" TRS you will always need to set the corresponding Apollo input to "LINE". When a particular input on an Apollo interface is set to LINE the Apollo takes signal from the 1/4" TRS connection corresponding to that channel. If you have your input set to LINE but are connecting via XLR, or if you have your input set to MIC but are connecting via 1/4" TRS, that would cause no input to show on the Apollo.
1/4" TRS should be used for all line level signals when possible. 1/4" TS connections should be avoided for line level signals.
The image below shows two Console input channels set to LINE in order to accept signal from the 1/4" TRS connections:
Connecting via 1/4" TS
1/4" TS is generally only used for Hi-Z connections such as electric guitar or bass. On all Apollo models (except Apollo 16) the Hi-Z input(s) on the front of the device are intended for use with 1/4" TS connections.
When you plug in a 1/4" TS cable to an Apollo Hi-Z input, that input channel automatically switches to Hi-Z and cannot be switched to MIC or LINE until the 1/4" TS cable is removed from the Hi-Z jack. While a 1/4" TS cable is plugged into a Hi-Z input, the corresponding XLR and 1/4" TRS connections for that input channel cannot be used.
The image below shows a Console input channel in Hi-Z mode:
Understanding Combo Jacks
Most Apollo models (except Apollo FireWire and Apollo 16) use combo jacks for their XLR and 1/4" TRS connections. These combo jacks combine an XLR and 1/4" TRS connection into a single jack to save space. These combo jacks may look a little bit different than your standard XLR or 1/4" TRS connections however they function just the same - when connecting via XLR set the corresponding input channel to MIC, and when connecting via 1/4" TRS set the corresponding input channel to LINE. Combo jacks accept all standard XLR and 1/4" TRS connectors.
Optical Connections vs. Coaxial Connections
Optical jack (ADAT or S/PDIF)
Coaxial S/PDIF jacks
We commonly get questions about using different digital input types with different Apollo models. Most Apollo models (except Apollo 16, Arrow,and Apollo Solo) feature optical ADAT input, however some Apollo models feature coaxial S/PDIF input while other models feature optical S/PDIF input. External devices always output ADAT as an optical signal, however some external devices output S/PDIF in optical format while other devices output S/PDIF in coaxial format. See the images above for examples of optical and coaxial connections.
On Apollo models that feature optical S/PDIF input - this includes Apollo Twin, Apollo Twin MkII, Apollo Twin X, and Apollo x4 - the same optical jack that is used for optical ADAT input is also used for optical S/PDIF input, meaning ADAT and S/PDIF cannot be used at the same time.
When sending S/PDIF signal from an external device into your Apollo, there are two things to take into consideration - the S/PDIF output type of your external device (optical or coaxial) and the S/PDIF input type of your Apollo device (optical).
Using External S/PDIF Signals with Apollo Twin, Apollo Twin MkII, Apollo Twin X, or Apollo x4
If using an Apollo Twin, Apollo Twin MkII, Apollo Twin X, or Apollo x4, first change the Digital Input to S/PDIF by going to Console > Settings > Hardware, clicking on your Apollo in the device list and selecting "S/PDIF" from the Digital Input menu:
If using an external device with an optical S/PDIF output (such as a gaming console, home stereo receiver, cable box, etc) use a standard optical cable (TOSLINK) to connect from the S/PDIF output of the external device to the optical input on the Apollo Twin, Apollo Twin MkII or Twin X.
If using an external device with a coaxial S/PDIF output (such as a rackmount CD player, turntable, etc), you will need to use a coaxial S/PDIF to optical S/PDIF converter to take the coaxial signal from the external device and convert it into an optical signal that can be accepted by the Apollo Twin, Apollo Twin MkII, Apollo Twin X, or Apollo x4. For examples of coaxial S/PDIF to optical S/PDIF converters, click here.