This is the Record Device Selector button.

Click this button and choose a command from the menu to select the sound card output you want to record.

Use the Audio device type control in the Audio Device page of the Preferences dialog to choose a recording device.

If you're using the Microsoft Sound Mapper as your default audio device, you can click the Record Device Selector and choose whether you want to record a stereo signal or only the left or right channel.

If you're using a device that has multiple input ports available, you can choose which port you want to record.

When you are ready to continue, click the Next button.