Yamaha AV-55 is a sound stereo amplifier that provides an immersive audio experience for music and home theater setups. It features a variety of input and output options, allowing you to connect multiple audio and video sources. With its surround sound capabilities, you can enjoy simulated surround effects from mono and stereo sources, or experience true surround sound when playing Dolby Surround encoded content. The amplifier also includes adjustable bass and treble controls, a balance control, and a bass extension switch for fine-tuning the sound to your liking.