Microphones and instruments such as guitars normally need to be recorded in mono. This is also referred to as "one channel" recording.
ACID and VEGAS, however, are set to record in stereo by default.
To record in mono and have the signal play on both speakers, follow these steps:

• Go to "Insert" > "Audio Track" to add an audio track to your project.
• Click the "Arm for Record" button in the track header of the audio track.

• To the left of this button is a speaker icon. This is the "Record Device Selector" button.
• Click this button and select "Left" or "Right" depending on which input your recording device is connected to.

This ensures that your mono signal is recorded correctly and is able to be played in your project.