Definition: MADI -- or Multichannel Audio Digital Interface -- is a recent development in digital audio transmission. MADI, as opposed to S/PDIF and AES protocols -- can transmit multi-channel audio in high-definition over coax or fiber optic lines. Unlike S/PDIF and AES protocols, you can send many channels of audio -- up to 64 per line. MADI is commonly used on today's digital multitrack recorders, digital live sound mixers, and digital performance systems that utilize multitrack technology.
MADI interfaces allow for transmission of very high-definition audio, up to 24-bit at 96 kHz resolution. You're also able to do very long cable runs with MADI interfaces -- up to 3,000 meters.
While it's use in smaller project studios is still limited, MADI compatibility is a feature we're likely to see more of in the near future.