The Line Audio CM4 is a small diaphragm condenser microphone that is designed for recording acoustic instruments and vocals. It is known for its excellent sound quality and wide frequency response, making it well-suited for capturing a wide range of sounds with clarity and detail. The CM4 is a cardioid microphone, which means that it is most sensitive to sound coming from directly in front of the microphone and less sensitive to sound coming from the sides or rear. It is a popular choice for recording acoustic guitar, piano, vocals, and many other instruments.