SACDs and DVD-Audio have up to 5.1 to 6.1 surround sound. Although both high-res optical formats have failed, there has been a resurgence in high-res digital files. SACD can be stored as a DSD file, and DVD-Audio can be stored as a FLAC or ALAC file. FLAC is the most widely used digital format for high-res with up to 8 channels and a maximum depth of 32 bit, and 655,350 Hz sampling rate. Uncompressed formats such as WAV and AIFF files can store audio CDs with no compression.