Behringer SRC2496 - Manual (Page 12)

12
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 European
Broadcast Union and in December 1985 by the Audio Engineering
Society (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 IEC 958 Type II (S/PDIF)
Connection XLR RCA/optical
Mode Balanced Unbalanced
Impedance 110 Ohms 75 Ohms
Level 0,2 V to 5 Vpp 0,2 V to 0,5 V pp
Clock
accuracy
Not specified
I: ± 50 ppm II: 0,1 %
III: Variable pitch
Jitter ± 20 ns Not specified
Tab. 4.1: Important data for AES and IEC 958 Type II
specifications
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 3 4 5 6 7
0 P/C Audio Locked
1
2
3
4
5
Bit
Emphasis Sampl. freq.
Channel mode Use of user bits
Use of AUX bits Sample length Reserved
Reserved for description of multichannel recording
Audio ref. Reserved
Reserved
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 3 4 5 6 7
0 P/C Audio Copy
1 Gen.st.
2
3
Bit
Emphasis Mode
Category code
Source number Channel number
Sampling frequency Clock acc. Reserved
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.
5. INSTALLATION