AES3 Data Format - 2.0 English

This section focuses on the standard two-channel PCM audio described in the AES3 specification.The basic data structure of AES3 is called a sub-frame. Each 32-bit sub-frame contains a single audio sample for one audio channel along with a few other bits of information as shown in the following figure. A sub-frame begins with a 4-bit preamble. The audio word can be either 24 bits or 20 bits. Following the audio word are the valid (V), user data (U), channel status (C), and parity (P) bits.

Figure 1. AES3 Subframe Format with 24-Bit Audio Sample

The preamble provides the start of the audio block (0x1) and audio channel information (0x2 - Channel 1 of pair and 0x3 - Channel 2 of pair). Bits[27:4] carry the audio data MSB bit at the 27th position and the LSB position is based on the audio sample length. Bit[28] provides the audio validity information. Bit[29] carries the user data information, and Bit[30] carries the channel status bit. Bit[31] is the even parity over 32 bits except for the preamble bits.

Two consecutive subframes, one for each of the two audio channels, form a complete frame. Frames are grouped together in blocks of 192 frames. This grouping of frames into blocks serves to define the beginning and ending points for the sequence of channel status and user data bits.