Please note that this tutorial was written for Logic Pro 9 and although the basic principles are likely to remain the same for future updates, some of the screenshots may not exactly match up with what you see in future versions.
To route an external audio signal to an audio track within Logic:
1. Navigate to Logic Pro → Preferences → Audio in the Logic menu bar.
2. Select the ‘Devices’ tab, and the ‘Core Audio’ sub-tab.
3. Under the ‘Input Device:’ drop-down menu, select the device that Logic will be receiving audio from (e.g. if you want to record audio from a microphone that is plugged into an audio interface, select the name of the audio interface in this menu).
NOTE: If you are using an external sound card, ensure that you have correctly installed all relevant drivers. Check the manufacturers website or the manual for full details.
4. Select ‘Apply Changes’ down at the bottom right of the Preferences window.
5. Select the audio track that you want to record to.
NOTE: You will firstly need to create an audio track to do this. To do this, select the '+' (add track) button above the track headers and select 'Audio', followed by 'Create'. Don't forget to set whether you want the track to be used for a mono or stereo signal.
6. In the relevant audio channel strip (either in the Inspector (to the left of the project screen) or in the Mixer) find the Label that says ‘I/O’.
7. Just under this label there should be two ‘slots’. The top slot is used to set a channel’s input. By default, it should display 'Input 1' for a mono track or 'Input 1-2' for a stereo track. Click it once so that a menu pops up and select the input that corresponds to where you are receiving audio from (e.g. if you want to record from a microphone that is plugged into Input 3 on your audio interface, select ‘Input 3’ from the input menu). The range of options in this box should mirror the number of inputs that your interface has... for example, if your interface only has 4 inputs, you should only be able to choose from 4 inputs in this box.
NOTE: You can also do this in the 'Add Track' window before you create the track.
NOTE: If you forgot to set the track up correctly, press the Format button in the track Inspector to toggle the track between mono and stereo format.
8. Press the small square ‘I’ button (either in the track header, the Inspector, or the mixer) and make some noise using the device connected to your selected input. You should see (and possibly hear depending on your set-up) that audio is coming into the selected channel by viewing the level meter next to the associated channel fader.
If you cannot see any audio coming into Logic, check that the input and main output levels on your interface are turned up to an adequate level. It is a good idea to start with the levels down and gradually turn them up, rather than start with the levels high, as this may result in an unexpected high signal level, that could potentially damage your equipment (and ears!)
You will also need to check that the device you are recording is plugged into the correct input on your interface. For example, many interfaces have different connections for microphones, guitars and line level devices. Some also have combo inputs, which combine two different types of connection into one combination socket. In this case, you need to make sure that you have your device plugged into the correct part of the socket. A typical example of this is an XLR/jack combo input, which generally provide an XLR connection for microphones and a 1/4" jack socket in the centre for guitars and/or line level instruments (e.g. synthesisers). In such cases, your interface may also have certain settings that need to be activated for specific purposes. For example, your interface may have a single socket for both line level and guitar signals, but it may have a switch to select which type of signal you will be recording as guitars require a high-impedance connection.
9. To record audio, deselect the ‘I’ button and select the Record 'R' button next to it...
10. ... then and press the 'Record' button in the Logic transport bar and after a count-in (if you have one set), you should see an audio waveform being created on the audio track as you record!