"Audio engineer" is a term usually used to identify the person in a music recording studio whose job it is to record live performances of music on tape or computer hard disk.
Audio engineers are also often referred to as recording engineers, but can also be mixing engineers or mastering engineers.
An audio engineer records live performances through a series of well-placed microphones which are hard-wired to a multi-channel console housed in a soundproof recording booth.
Some artists try to record their music at home, with inexpensive "studio-in-a-box" machines. The advantage to professional audio engineering is the use of top-flight equipment and the talents of someone who is an expert in the field.
Different types of audio engineers have different tasks. The mixing engineer is responsible for mixing the various tracks of a song into a pleasant final product. The mastering engineer is responsible for fine-tuning the two-track stereo recording, usually by frequency equalization and sound compression.