Kurzweil DMTi

Designed to interface the Kurzweil K2000/K2500 synths directly with digital recording equipment, the DMTi also has a role as a general‑purpose digital format convertor. Hugh Robjohns checks it out.

The DMTi was originally conceived to support the Kurzweil K2500 series of synthesizers with the KDFX digital expansion board (reviewed SOS January 1999) fitted. As well as adding good‑quality effects to the keyboard, this expansion card also provides four individual stereo digital audio outputs in a proprietary format called KDS (Kurzweil Digital Stream). The DMTi can accept these digital signals and convert them into any of the more familiar digital audio formats (depending on the configuration of the unit), thereby allowing a direct digital interface with mixing consoles and other recording equipment in 16‑bit resolution.

The DMTi has also been designed to address the thorny problem of digital synchronisation: consequently, it features eight channels of sample‑rate conversion using Analog Devices AD1893 chips. Although it was designed to support the K2500 series, the unit can also be used as a stand‑alone format converter, exchanging signals to and from AES‑EBU, S/PDIF, and either ADAT or TDIF formats — with sample‑rate conversion if required.

Cook's Tour

Essentially, the DMTi is a very simple rackmounting 4‑way stereo digital router. The controls consist of four rotary switches on the front panel, to select which source is routed to which output, and a clock source selector. There is no memory facility, no automatic clock selection routine, nor any kind of LCD display with menu options. In fact, the only LED on the entire machine is a power‑on indicator. Technophobic musicians who reluctantly accept the need to go digital may find this the perfect interfacing tool.

The unit accommodates four stereo input channels from a KDS synth interface, four paired channels from a modular digital multitrack (TDIF or ADAT depending on which card is installed in the DMTi) and a pair of stereo AES‑EBU inputs. Outputs are available on four AES‑EBU ports, the KDS connector, and the digital multitrack card. The clock source can be selected from an internal oscillator (either 44.1 or 48kHz), any of the inputs, or an external word‑clock reference. Built‑in sample‑rate conversion allows non‑synchronous digital sources to be used within a properly clocked system and reduces the amount of cabling and general messing about needed to interface otherwise incompatible equipment.

Rear Window

The rear panel of the DMTi is fairly busy, as you might expect. On the left‑hand side are a pair of XLRs for the two AES‑EBU inputs, plus a TOSlink optical connector. A recessed slide switch reallocates the first AES‑EBU input port to accept optical S/PDIF‑format signals, providing a useful degree of flexibility. On the right is the slot for an ADAT or TDIF interface plug‑in card, as mentioned above. The review machine was supplied with the ADAT interface, which provides the usual pair of optical sockets for the ins and outs, plus a pair of 9‑way D‑Sub connectors for a hard‑wired alternative.

Across the centre of the rear panel are four male XLRs providing the four stereo channels of digital outputs in AES‑EBU format. The signal from the first AES‑EBU output port is also available on an adjacent optical TOSlink connector, and can be switched independently from the front panel to carry either consumer or professional formatted data. The remaining three outputs can also be reformatted, but are switched together.

The Kurzweil KDS interface consists of a pair of 15‑way D‑Sub connectors, one for the four stereo inputs (called A, B, C and D) and the second for four outputs plus a special stereo return signal (which is the same as output 1). Next to these are a pair of BNCs accommodating word clock input and output, and a standard IEC mains socket.

Front End

The front panel couldn't be any simpler. To the left is the on/off push‑button, next to which are four rotary switches to select the digital source feeding each of the four output destinations. The first switch determines the signals routed to AES 1, MDM 1&2 (ie. ADAT or TDIF 1&2), KDS A, and the KDS return. The second sends signals to AES 2, MDM 3&4, KDS B... and so on. The same 10 input sources are available to each output: AES 1, AES 2, MDM 1&2, 3&4, 5&6, 7&8, KDS A, B, C, and D. A slide switch selects pro or consumer format for output 1, and a similar switch provides the same function for outputs 2‑4.

The last control is the 'output sync clock selector' which is a rotary switch providing two internal clock sources (44.1 and 48kHz), external word clock, or clocks derived from either of the two AES inputs, the MDM interface, or the KDS port. I was surprised to find that there's no indicator to show when the unit has found and locked to an acceptable clock source: such an indicator would make me a lot more confident that the DMTi was working properly!

Conclusion

Although I didn't have a K2500 system to try while testing the DMTi, I was able to check the unit with my own digital studio system. I used it to interface with a Yamaha 03D, an ADAT recorder and a Korg Soundlink PCI card in a Mac workstation, as well as various other bits of digital equipment using the AES‑EBU and S/PDIF formats. In all cases, it appeared to function as expected, without any problems at all. The sample‑rate conversion seemed effective and glitch‑free, and the signal routing was simple and effective.

Clearly, the DMTi really comes into its own as an interface for the K2500 synths, allowing a digital link straight to either a modular digital multitrack or recording console, and permitting signals to be returned to the K2500 for on‑board effects processing. In this rather specialised context I can accept the machine as being well worth its asking price. As a stand‑alone format convertor, however, it's not quite as flexible as, say, the Spectral Translator or the Otari UFC24 which can exchange data directly between ADAT and TDIF formats as well as a host of other interfaces — albeit without sample‑rate conversion.

On the other hand, if you only need to convert between ADAT and AES‑EBU (or TDIF and AES‑EBU) this unit is just the ticket, and its built‑in sample‑rate conversion would do away with the problems caused by incompatible sample rates. Furthermore, it allows semi‑pro or consumer equipment without external clock reference inputs to be interfaced to a properly synchronised digital installation very easily and effectively. It's a shame the unit is limited to only 16‑bit operation, and I hope Kurzweil are thinking about releasing a 20/24‑bit version in the future.