Alesis Digital Audio Tape or ADAT, first introduced in 1991, was used for simultaneously recording eight tracks of digital audio at once, onto Super VHS magnetic tape – a tape format similar to that used by consumer VCRs. Greater numbers of audio tracks could be recorded by synchronizing several ADAT machines together. While this had been available in earlier machines, ADAT machines were the first to do so with sample-accurate timing – which in effect allowed a studio owner to purchase a 24-track tape machine eight tracks at a time. This capability and its comparatively low cost were largely responsible for the rise of project studios in the 1990s.
Several versions of the ADAT machine were produced. The original ADAT (also known as “Blackface”) and the ADAT XT recorded 16 bits per sample (ADAT Type I). A later generation of machines – the XT-20, LX-20 and M-20 – supports 20 bits per sample (ADAT Type II). All ADAT’s use the same high quality S-VHS tape media. Tapes formatted in the older Type I style can be read and written in the more modern machines, but not the other way around. Later generations record at two sample rates, 44.1 kHz and 48 kHz, although the original Blackface could only do 48 kHz. Most models allow pitch control by varying the sample rate slightly (and tape speed at the same time).