Editing AES3 (section)

===Channel status word===
There is one channel status bit in each subframe, a total of 192 bits or 24 bytes for each channel in each block. Between the AES3 and S/PDIF standards, the contents of the 192-bit channel status word differ significantly, although they agree that the first channel status bit distinguishes between the two. In the case of AES3, the standard describes, in detail, the function of each bit.<ref name="AES-EBU-3250-E" />

*Byte 0: Basic control data: sample rate, compression, emphasis
**bit 0: A value of 1 indicates this is AES3 channel status data.  0 indicates this is S/PDIF data.
**bit 1: A value of 0 indicates this is linear audio PCM data.  A value of 1 indicates other (usually non-audio) data.
**bits 2–4: Indicates the type of signal [[preemphasis]] applied to the data.  Generally set to 100{{sub|2}} (none).
**bit 5: A value of 0 indicates that the source is locked to some (unspecified) external time sync.  A value of 1 indicates an unlocked source.
**bits 6–7: Sample rate.  These bits are redundant when real-time audio is transmitted (the receiver can observe the sample rate directly), but are useful if AES3 data is recorded or otherwise stored.  Options are unspecified, 48&nbsp;kHz (the default),  44.1&nbsp;kHz, and 32&nbsp;kHz. Additional sample rate options may be indicated in the ''extended sample rate'' field (see below).
*Byte 1: indicates if the audio stream is stereo, mono or some other combination.
**bits 0–3: Indicates the relationship of the two channels; they might be unrelated audio data, a stereo pair, duplicated mono data, music and voice commentary, a stereo sum/difference code.
**bits 4–7: Used to indicate the format of the user channel word
*Byte 2: Audio word length
**bits 0–2: Aux bits usage.  This indicates how the aux bits (time slots 4–7) are used.  Generally set to 000{{sub|2}} (unused) or 001{{sub|2}} (used for 24-bit audio data).
**bits 3–5: Word length.  Specifies the sample size, relative to the 20- or 24-bit maximum.  Can specify 0, 1, 2 or 4 missing bits.  Unused bits are filled with 0, but audio processing functions such as mixing will generally fill them in with valid data without changing the effective word length.
**bits 6–7: Unused
*Byte 3: Used only for multichannel applications{{elucidate|date=June 2020}}
*Byte 4: Additional sample rate information{{elucidate|date=June 2020}}
**bits 0–1: Indicates the grade of the sample rate reference, per [[AES11]]
**bit 2: Reserved
**bits 3–6: Extended sample rate.  This indicates other sample rates, not representable in byte 0 bits 6–7.  Values are assigned for 24, 96, and 192&nbsp;kHz, as well as 22.05, 88.2, and 176.4&nbsp;kHz.
**bit 7: Sampling frequency scaling flag. If set, indicates that the sample rate is multiplied by 1/1.001 to match [[NTSC]] video frame rates.
*Byte 5: Reserved
*Bytes 6–9: Four [[ASCII]] characters for indicating channel origin.  Widely used in large studios.
*Bytes 10–13: Four ASCII characters indicating channel destination, to control automatic switchers.  Less often used.
*Bytes 14–17: 32-bit sample address, incrementing block-to-block by 192 (because there are 192 frames per block).  At 48&nbsp;kHz, this wraps approximately every day.{{efn|Exactly 24&nbsp;h 51&nbsp;min 18.485333&nbsp;s}}
*Bytes 18–21: 32-bit sample address offset to indicate samples since midnight.<ref>{{cite web|url=https://tech.ebu.ch/docs/tech/tech3250.pdf|title=Specification of the AES/EBU digital audio interface (The AES/EBU interface)|publisher=European Broadcast Union|year=2004|access-date=2014-01-07|page=12 |quote=Bytes 18 to 21, Bits 0 to 7: Time of day sample address code. Value (each Byte): 32-bit binary value representing the first sample of current block. LSBs are transmitted first. Default value shall be logic "0". Note: This is the time-of-day laid down during the source encoding of the signal and shall remain unchanged during subsequent operations. A value of all zeros for the binary sample address code shall, for the purposes of transcoding to real time, or to time codes in particular, be taken as midnight (i.e., 00 h, 00 min, 00 s, 00 frame). Transcoding of the binary number to any conventional time code requires accurate sampling frequency information to provide the sample accurate time.}}</ref>
*Byte 22: Channel status word reliability indication
**bits 0–3: Reserved
**bit 4: If set, bytes 0–5 (signal format) are unreliable.
**bit 5: If set, bytes 6–13 (channel labels) are unreliable.
**bit 6: If set, bytes 14–17 (sample address) are unreliable.
**bit 7: If set, bytes 18–21 (timestamp) are unreliable.
*Byte 23: [[Cyclic redundancy check|CRC]].  This byte is used to detect corruption of the channel status word, as might be caused by switching mid-block.{{efn|Generator polynomial is ''x''<sup>8</sup> + ''x''<sup>4</sup> + ''x''<sup>3</sup> + ''x''<sup>2</sup> + 1, preset to 1.}}