Behringer SRC2496 5.INSTALLATION, XLR, Bit, P/C, Bit, P/C, Type, Mode, Mode, Level, Clock, Jitter, Locked, AES/EBU, 75 Ohms, ± 20 ns, Channel, Balanced, 110 Ohms, accuracy

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 quantity would far exceed any hardware capacity. 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	Not specified	I: ± 50 ppm II: 0,1 %
accuracy		III: Variable pitch
Jitter	± 20 ns	Not specified

Tab. 4.1: Important data for AES and IEC 958 Type IIspecifications

Table 4.2 illustrates part of the structure of the professional format, as it would normally be used with AES/EBU connections.

Byte						Bit
	0		1	2	3		4	5	6	7
0	P/C		Audio	Emphasis				Locked	Sampl. freq.
1			Channel	mode				Use of user bits
2	Use of AUX bits					Sample length			Reserved
3		Reserved for description of multichannel recording
4	Audio ref.						Reserved
5					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					Bit
	0	1	2	3		4	5	6		7
0	P/C	Audio	Copy		Emphasis				Mode
1			Category code							Gen.st.
2		Source number					Channel number
3	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 piece of equipment, such as a commercially available DAT recorder, has only one S/PDIF input, the equipment 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 equipment 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). A lot of equipment has no stop function while other equipment 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

5.1General 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 piece of equipment.

Unlike digital connectors, analog connectors are not galvanically separated, but have a balanced design and are thus unproblematic in regard to ground loops.

5.2 Analog inputs and outputs

In order to give your audio signals the best possible protection from electromagnetic interference, the ULTRAMATCH PRO has balanced XLR inputs and outputs. As previously described, the level at the analog inputs can be adjusted with the GAIN control. The outputs operate at studio level (+4 dBu). Please see the following illustrations for the pin assignment of the connectors.

Of course, it is also possible to send signals to the SRC2496 from unbalanced outputs (e.g. sound cards or mixing console outputs) in order to further process them in digitized form. Receiving analog signals (e.g. when using a high-end D/A converter between a CD-Player and amplifier) from the ULTRAMATCH PRO via unbalanced connectors (e.g. hi-fi amplifier or tape recorder) is not a problem, too.

12 5. INSTALLATION