Photos: Mark Ewing
Traditional patchbays can be great for managing signal routing between various AES-EBU and coaxial S/PDIF digital devices, but patchbays aren't really very practical for optical S/PDIF or ADAT lightpipe connections, partly because of the mechanical fragility of the connectors and the relative scarcity of Toslink couplers. In many ways, a better technique to patch any kind of signal is via an electronic router, and, although this approach is rarely cost-effective for analogue signals, it is far and away the best solution for digital signals ’Äî not least because of the reclocking features built into most units. The Apache unit on review here is manufactured by the American Frontier Design group, probably best known for its range of soundcards and interfaces. It provides a 12 x 12 routing matrix with all inputs and outputs connected via Toslink optical ports.
The unit handles the input data in a totally transparent way, so it does not care whether the signal is formatted to carry stereo S/PDIF or eight-channel ADAT signals (or even one of the alternative ADAT formats. I suspect most users would employ the Apache to route multi-channel ADAT signals between mixers, hard disk recorders, and computer workstations ’Äî accommodating up to 96 channels of audio in and out. However, the fact that it can also route optical S/PDIF signals means that a portion of the matrix could also be used to interface stereo replay machines for monitoring, and mastering recorder feeds as well. The best part, though, is that all the input and output connections are instantly reconfigurable with just a couple of button presses.
The Apache is a slim 1U rackmount router contained within a sturdy metal case with an integral mains power supply. It has 24 Toslink optical ports mounted across the rear panel, each protected from dust with the familiar plug-in stopper. A pair of MIDI sockets allow control and preset data to be exchanged with a computer, as well as allowing the interlinking of multiple routers. Mains power is supplied through the usual IEC inlet, and a mains voltage selector switch is accessible through a small cut-out tucked away on the side panel.
Each input circuit is completely independent from all the rest in terms of both clocking and data format. This means that there is no requirement for all sources or destinations to be synchronised to the same word clock, and S/PDIF and ADAT optical signals can be routed simultaneously from different inputs to different outputs. The unit essentially transfers the input data directly to the appropriate outputs unchanged, so ADAT data-packing formats such as SMUX, PAQRAT and so on can be handled transparently. However, there is no capability for format-conversion between S/PDIF and ADAT signals, or for the decoding of any of the bespoke ADAT formats. Any data word length can be accommodated up to 24 bits in both S/PDIF and ADAT formats, as can sample rates up to 96kHz. The input signals are carefully reclocked before being dispatched through the selected outputs to reduce interface jitter.
The black front panel is covered in black buttons, but the status of the unit is made clear through no less than 30 red LEDs. The unit is switched on via a rocker switch on the left-hand side of the panel and the current operational function is determined by a row of five square buttons. The 12 inputs and outputs each have an associated round button which is used mainly for routing assignments, although some of these buttons also have roles in configuring the MIDI aspects of the unit.
The five status buttons are labelled Store, Recall, MIDI, Patch and Status, and their functions and operation are pretty intuitive. The unit can store up to twelve patching assignments internally, recalled and stored using the appropriate status buttons in concert with one of the twelve input selector buttons. It seems odd that only twelve (rather than 24) presets are available, but in practice twelve different wiring configurations should be more than sufficient for most applications, especially if working with 24-channel equipment. If required, additional presets can be stored in a computer and downloaded via the MIDI interface using SysEx commands.
The Patch button activates the signal patching mode, which can be based on either input routing or output routing, whichever is the more appropriate. The input patch mode is activated by pressing any one of the twelve input selector buttons immediately after pressing the Patch status key. The selected input is indicated by its corresponding LED flashing slowly, while all the assigned output destinations are also illuminated. Pressing any of the output buttons toggles the connection on or off, as appropriate. An input signal can be routed to any number of output destinations, but each output can only accept a single source ’Äî there is no facility for mixing signals within the router.
The output patch mode works in a similar way: after selecting the Patch button, any output selector can be pressed. The selected output LED will flash and if any source has been assigned to it, that will also light up, along with any other output destinations to which that input signal has also been assigned. It's all very intuitive and logical in practice, and configuring the router is very straightforward.
The Status button is used to activate one of two status monitoring modes (each press of the button toggles to the other mode): Scanning Status and Activity Status. In the former mode each input LED lights in turn, from one to 12 and back to one again, with the corresponding output destinations illuminating to show each patch configuration. At the same time, the brightness of the input LED indicates the presence (bright) or absence (dim) of data at that input ’Äî if the data is in ADAT format then the separate ADAT LED also lights.
In Activity Status mode the input and output LEDs are used to display the presence and format of the data present on each input and output, simultaneously. If there is no signal present on an input, or if an output channel has not been assigned to an input source, then its corresponding LED is off. If the data is in the S/PDIF format (or is a mute ADAT signal) the LED is illuminated dimly, while ADAT signals carrying audio on one or more channels (higher than -48dBFS) are shown with brightly lit LEDs.
Pressing the MIDI button immediately reveals the MIDI device ID number for the unit, and whether MIDI data is being received. The device number is indicated by the corresponding input channel LED, while the LED for output channel one is illuminated brightly when MIDI data is being received and dimly if the unit detects a source using MIDI active sensing. The buttons for output channels two and three are used to configure the machine's settings when the Apache is cascaded with other units to expand the I/O. The channel-two button toggles Slave mode (which also disables the front-panel status buttons), while the channel-three button enters Duplicate Device ID mode (see the 'Send Reinforcements' box for more details).
Although the Apache doesn't have a MIDI Thru port, data presented at the input is automatically passed to the output (with a propagation delay of about 1ms). Every aspect of the machine can be controlled via MIDI SysEx messages, either by globally addressing any and all Apache machines, or by directing commands to specific machines according to their individual device IDs. Units can also be instructed to dump current preset patches over MIDI, or to receive new patches in the same way. The handbook provides precise details about the structure and values of the required SysEx messages. Alternatively, the Apache can be forced to perform a SysEx dump of its patch presets by pressing the MIDI status button followed by output button 12.
Send Reinforcements: Cascading Multiple Units
For installations requiring more than 12 optical I/O ports it is possible to connect multiple Apache units together, using MIDI data to communicate between units. Once connected, and with one unit designated the 'master', pressing any status button on the master unit will select the same mode on all the slave units.
There are two possible configurations for linking multiple Apache units: each machine can either have a unique device ID, or they can all share the same device ID. In the first configuration each switch point can be addressed directly and individually, either manually by pressing the appropriate input and output buttons on each unit, or via computer. In the second mode all the slave Apache units do whatever the master unit does.
When configured with individual device IDs, each Apache can have independent patch configurations stored in each preset, but changing the preset on the master Apache recalls the same numbered preset to all Apaches. The outputs of one unit can be patched directly to the inputs of another, if required, to enable signals to be routed through the interconnected Apaches to any or all outputs, as necessary ’Äî although there are obvious restrictions to the number of available routing paths.
The Duplicate Device ID mode is for use when the Apache units are configured as a multi-layer matrix ’Äî imagine the units stacked one above the other. In this mode the routing from inputs to outputs is reflected identically on all of the units. So if you wanted to route 24 channels of ADAT signal you could configure three Apaches in the Duplicate Device ID mode, with channels 1-8 handled by the master unit, 9-16 on the second unit and 17-24 on the third. With this arrangement there would be no way to route channels 17-24, say, to outputs 1-8, but the advantage would be considerably more input and output ports. Clearly, different kinds of installations will benefit from different configurations, but the Apache system is sufficiently flexible to cater for pretty much any multi-unit requirements.
The handbook provides lots of useful advice and clear examples of the best ways to configure the Apache, either individually or in cascade with others, and a set of blank paper templates are provided to help plan and document the various patches and preset configurations. I found setting the unit up very straightforward, provided that a little paper planning was done first. I tested the Apache by using it as an input and output expander for the optical ports of my Apogee PSX100 converter, so I found it particularly handy that the Apache could accommodate both S/PDIF and ADAT data.
Using a Digispy digital signal analyser, I was able to confirm that the Apache had no deleterious effect on data quality, and in cases where the source suffered high levels of jitter (because an excessively long or poor-quality lightpipe was used) the signal quality rating actually improved, thanks to the built-in reclocking circuitry. Recalled patches appear to change instantaneously, but where the input data streams are not synchronous brief glitches can be heard at the switching instant. Some equipment receiving data from the Apache may also mute briefly, as it has to try to resynchronise to the incoming word clock embedded in the data stream.
Although I'm sure some users will find the feature useful, personally I found the continuous Scanning Status mode rather distracting. Instead, I preferred to set the unit to the Activity Status mode, which I found very handy for providing at-a-glance information that the patch was correct and that data was flowing, especially when working with ADAT-format signals. The ability to control the Apache via MIDI is useful, not just as a means of extending the available preset memories, but also for coordinating particular signal-routing assignments alongside the scene memories of a digital mixer or a specific project within a workstation. I'm no MIDI expert, but fortunately the handbook provides precise and detailed information about how to construct the necessary SysEx messages for direct control of the Apache from the MIDI controller of your choice.
The bottom line is that, if your studio is interfaced largely with ADAT lightpipes, the Apache is a very convenient and practical way of increasing the flexibility and reliability of the installation, while also handling stereo S/PDIF signals with equal aplomb, perhaps for monitoring sources and two-track record outputs. This is a powerful and flexible product which won't break the bank, and is certainly worthy of closer inspection by anyone with more than a small handful of lightpipe connections.