The Sony TC-707SD is a portable audio cassette player and recorder released by Sony in the late 1990s. It is part of Sony's popular Walkman line of products. The TC-707SD features advanced sound processing technology, such as digital noise reduction and bass boost, to enhance audio playback and recording quality. It also has a built-in microphone for recording, and can automatically adjust recording levels to prevent distortion. Other features include variable speed recording, Dolby noise reduction, and the ability to record in mono or stereo. The TC-707SD is compatible with standard audio cassette tapes and requires AA batteries or an AC adapter for operation. It is often sought after by audio enthusiasts and collectors due to its high sound quality and retro design.