Aes/Ebu And S/Pdif Standards; Installation; General Connection Notes - Behringer Ultramatch PRO SRC2496 User Manual

ULTRAMATCH PRO SRC2496
There is no doubt that digital signal processing guarantees the
lowest distortion and noise values. However, up until now signal
conversion, specifically sampling rate conversion, had partially
led to considerable distortion and interference: If you tried to use
traditional methods, the incoming data would be far in excess of
any hardware dimensions. If data was put into smaller pieces, to
avoid storage problems, the necessary turnaround time would
prevent any practical application. Therefore, programmers
continue to experiment with the most varied of algorithms, ending
up, however, always having to make a compromise between
computation efforts and sound quality.
By processing data in real time, the processor used in the
BEHRINGER ULTRAMATCH PRO can process incredible
amounts of data.
The noise and interference floor is thus below -117 dBFS, and
the distortion values, even with difficult input signals, are below
-104 dBFS. The ULTRAMATCH PRO remains practically inaudible
as such values are not normally achieved either by the A/D or the
D/A converter, and certainly not by the CD as the final product.

4.2 AES/EBU and S/PDIF standards

In principle there are two standards, the most important electrical
characteristics of which can be seen in tab. 4.1.
AES/EBU is the professional, balanced connection via XLR
connectors. This interface is based on two identical protocols
published in November 1985 (EBU Tech. 3250-E) by the uropean
roadcast nion and in December 1985 by the udio ngineering
ociety (AES3-1985). Sony and Philips oriented themselves to this
standard and developed a further interface with unbalanced signal
routing and a few other major differences, predominantly related to
the assignment of the channel status bits. This interface, named
after the two companies and known as S/PDIF (Sony/Philips Digital
Interface), uses either RCA connectors or optical connections with
optical fiber cables. The procedure, standardized in IEC 958, made
a name for itself mainly due to efforts to introduce a copy protect
technique. This standard also describes the revised AES/EBU
interface, which was adapted to the S/PDIF format and named
IEC 958 Type I (professional). The name of the S/PDIF interface is
then IEC 958 Type II (consumer). Your ULTRAMATCH PRO uses
the latest versions of each of the standards, AES/EBU (AES3),
IEC 60958 and EIAJ CP-1201 (Japanese standard).
Type AES/EBU
Connection XLR
Mode Balanced
Impedance 110 Ohms
Level 0,2 V to 5 Vpp
Clock
Not specified
accuracy
Jitter ± 20 ns
Tab. 4.1: Important data for AES and IEC 958 Type II
specifications
12
IEC 958 Type II (S/PDIF)
RCA/optical
Unbalanced
75 Ohms
0,2 V to 0,5 V pp
I: ± 50 ppm II: 0,1 %
III: Variable pitch
Not specified

5. INSTALLATION

Table 4.2 illustrates part of the structure of the professional
format, as it would normally be used with AES/EBU connections.
Byte
0 1 2
Emphasis
0 P/C Audio
1 Channel mode
Use of AUX bits
2
Reserved for description of multichannel recording
3
Audio ref.
4
5
Tab. 4.2: Markers in professional format (AES/EBU)
Table 4.3 presents the corresponding consumer-format data,
as normally used with S/PDIF-connections.
Byte
0 1 2
0 P/C Audio Copy
Category code
1
Source number
2
Sampling frequency
3
Tab. 4.3: Markers in consumer format IEC 958 Type II (S/PDIF)
The first bit already defines whether the following bits are to be
understood as professional or consumer-format bits. As shown,
the audio information can be found at the same position in the
data stream, in principle making both formats compatible. There
are, however, information blocks that differ in both norms. If a
device, such as a commercially available DAT recorder, has only
one S/PDIF input, the device will usually understand that format
only. It will thus usually stop when supplied with professional-format
data. The reason is simple: as shown in the illustrations, processing
a professionally-coded signal with a device that can only
understand consumer format can lead to malfunctions relating to
the copy protect bit and the emphasis!
However, this point is not always readily evident, as is the case
with plug-and-socket connectors (e.g. 1/4" TRS connectors, mini-
jacks and special adapters for Sub-D instead of XLR connectors).
Many devices have no stop function while others can understand
both formats despite having only one type of connector.
In all of these cases using the ULTRAMATCH PRO as the
ultimate problem solver will soon pay off. Virtually, all common
digital signals it receives at the input appear at the output with
new, clean markers in the respective chosen format.
5. INSTALLATION

5.1 General connection notes

The ULTRAMATCH PRO’s digital input and output connections
are short-circuit proof and transformer-balanced. This rules out
any possibility of ground loops caused by additional ground
connections, even when using the RCA connectors. Furthermore,
the completely potential-free concept of the digital connectors
allows for using adapters in order to, e.g. route the RCA connector
signal to the XLR input of another device.
Bit
3 4 5 6
Sampl. freq.
Locked
Use of user bits
Sample length Reserved
Reserved
Reserved
Bit
3 4 5 6
Emphasis Mode
Gen.st.
Channel number
Clock acc. Reserved
7
7