Lesson 12

Digital Audio Formats

An audio interface will have a limited number of channels available for the ad/da conversion. Many interfaces will provide an expansion option to receive digital audio from another device that does the conversion, so the interface is capable of providing more channels to the daw, but doesn’t have to provide conversion for all of them.
The advantage of this is added flexibility in multi channel setups. Often, devices such as keyboards and preamps will offer digital outputs, which can be connected the digital inputs of the interface and not use up any of the precious analog inputs of the interface.

The most common forms of digital audio are AES/EBU, Adat, and Spdif.

Adat uses an optical cable to transmit the digital information. This single cable can transmit 8 channels of 24 bit audio at 44.1 or 48 kHz.
It’s important to remember, that 88.2 or 96 kHz contains twice as much information per channel, and therefore the Adat cable can only stream half as many channels. So, at 88.2 or 96 khz, an Adat cable can only stream 4 channels of audio, and at 176.4 or 192 kHz it can only stream 2 channels.

The AES/EBU format uses a single Xlr cable to transmit 2 channels of digital audio at any sample rate, and is capable of longer cable runs than ADAT. Often, a DB-25 connector will be used, which is a single connector that essentially houses 8 xlr cables. A single DB-25 connector is capable of transmitting 16 channels of digital audio at any sample rate. 
The AES/EBU protocol can also transmit word clock information along with the digital audio, which adds flexibility and convenience for syncing Word Clock.

SPDIF is similar to AES/EBU, however it uses an unbalanced cable with rca connectors. This digital audio format can also transmit 2 channels of digital audio at any sample rate, however, compared to AES/EBU, it is more susceptible to to interference and the cable length must be kept as short as possible.