RME OCTAMIC XTC [54/62] Aes ebu spdif

User’s Guide OctaMic XTC © RME

22.6 AES/EBU - SPDIF

The most important electrical properties of 'AES' and 'SPDIF' can be seen in the table below.

AES/EBU is the professional balanced connection using XLR plugs. The standard is being set

by the Audio Engineering Society based on the AES3-1992. For the 'home user', SONY and

Philips have omitted the balanced connection and use either Phono plugs or optical cables

(TOSLINK). The format called S/P-DIF (SONY/Philips Digital Interface) is described by IEC

60958.

Type AES3-1992 IEC 60958

Connection XLR RCA / Optical

Mode Balanced Unbalanced

Impedance 110 Ohm 75 Ohm

Level 0.2 V up to 5 Vpp 0.2 V up to 0.5 Vpp

Clock accuracy not specified

I: ± 50 ppm

II: 0.1%

III: Variable Pitch

Jitter < 0.025 UI (4.4 ns @ 44.1 kHz) not specified

Besides the electrical differences, both formats also have a slightly different setup. The two

formats are compatible in principle, because the audio information is stored in the same place in

the data stream. However, there are blocks of additional information, which are different for both

standards. In the table, the meaning of the first byte (#0) is shown for both formats. The first bit

already determines whether the following bits should be read as Professional or Consumer

information.

Byte Mode Bit 0 1 2 3 4 5 6 7

0 Pro P/C Audio? Emphasis Locked Sample Freq.

0 Con P/C Audio? Copy Emphasis Mode

It becomes obvious that the meaning of the following bits differs quite substantially between the

two formats. If a device like a common DAT recorder only has an SPDIF input, it usually under-

stands only this format. In most cases, it will switch off when being fed Professional-coded data.

The table shows that a Professional-coded signal would lead to malfunctions for copy prohibi-

tion and emphasis, if being read as Consumer-coded data.

Nowadays many devices with SPDIF input can handle Professional subcode. Devices with

AES3 input almost always accept Consumer SPDIF (passive cable adapter required).