The FSSD audio format is a proprietary audio format used by SoundCap, which is a software tool for analyzing acoustic signals. The FSSD format is used by SoundCap to store recorded audio data along with its associated metadata. The FSSD format is a binary format, which means that it is not human-readable and can only be opened and processed by software that is specifically designed to work with it, such as SoundCap. The FSSD format stores audio data in a compressed form, which allows for efficient storage of large amounts of audio data. If you have a FSSD audio file and you want to work with the audio data in the file, you will need to use SoundCap or a compatible software tool that can read and process the FSSD format.