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RME Designs

Matthias Carstens & Stephan Flock
Published July 2005
By Paul White

From simple beginnings as an offshoot of an electronics project, RME have established themselves as soundcard and recording interface manufacturers whose products are almost always reliable, and usually offer that bit more than those of their competitors. We talk to their head of development about their recent innovations.

It would be too easy to dismiss RME as just another one of those worthy but unexceptional companies that produce soundcards or audio interfaces, but behind the company is a very dedicated team of audio engineers with a whole range of technical and artistic skills. For example, Stephan Flock, who is the company's main digital designer, is also a concert pianist and classical recording engineer with a Grammy award to his credit. RME regard themselves not as a manufacturing company but rather as a design and development team, and today, the equipment that bears their name is marketed by European distributor Synthax, with whom they enjoy a symbiotic relationship.RME head of development, Matthias Carstens.RME head of development, Matthias Carstens.

RME's latest range of products makes a good showcase for the company's technical approach to product design and there are several 'under the hood' innovations that were explained to me when I interviewed Matthias Carstens, RME's head of development, and Stephan Flock, the company's digital design guru.

In The Beginning

I was curious to know what career path Matthias had taken that had ended up with him founding and running RME. He explained as follows: "I trained as an electronic engineer, played drums in bands and also developed an interest in recording. I later worked in a music store, where I gained a reputation as a good repair man, and eventually went on to become head product designer for Behringer, where I designed the Edison, the Supressor, the Ultramatch and my personal favourite, the Combinator, a four-way compressor/limiter with more than 2000 components inside. My last development for the company was a piece of tube circuitry which allowed harmonics to be added in a controlled way." Matthias has also worked as a journalist and editor for the former highly regarded German electronics magazine ELRAD, as well as contributing many articles to the country's top computer mag, so he has what you might call a well-rounded background.

So how did RME get started? "In 1996 a project was presented for publication in ELRAD by a young East German man who had developed a small pice of equipment called the DAM1 (Digital Audio Monitor). The design was published as a DIY project, but I thought we should build it in quantities and sell it". The author, Ralf Männel, agreed, and that was the start of RME. Ralf specialises in DSP code, and designed the DAM1, the ADI96 Pro, DIGICheck and the HDSP Meter Bridge.

"Also In 1996, two brothers named Kirst got in contact with ELRAD about a PCI recording card design. I contacted them and convinced them that they could earn some money if the products were improved and built in quantity. Martin Kirst studied electronics, plays organ in churches, and changed his name to Björnsen when he married. Martin developed the Hammerfall hardware and wrote all the Windows and Mac drivers for our products. Uwe Kirst has worked on most major projects together with his brother Martin. His latest contribution to RME is the Fireface hardware and parts of the Fireface Windows driver.

"I found a very small manufacturer, Ingenieurbüro Müller, located in Mittweida, who agreed to build the DAM1 and the PCI recording card in small quantities for a reasonable price. Today, IMM still build all our products, but their small company has now grown to more than 100 people. Then we needed a distributor in Germany, and Synthax's name came up — Hermann Savon, the MD, had a good reputation for being a serious business partner. Two months later, I was part of his booth at the Frankfurt Musikmesse!

"The DAM turned out to be a disaster, as nobody wanted it, but our recording card, the DIGI32, sold quite well and quickly gained a good reputation. Later, we added an analogue monitoring output to this card, and in February 1998 the DIGI32 Pro was launched as the world's first 96kHz audio card! At RME we were also first with 24-bit NT drivers, Interrupt sharing support, ASIO hardware, a multi-channel solution under Windows NT and Linux, and ASIO Direct Monitoring."

RME's digital designer and engineer Stephan Flock overseeing a choral recording in London. Unsurprisingly, you can see some RME hardware in the rack in the background!RME's digital designer and engineer Stephan Flock overseeing a choral recording in London. Unsurprisingly, you can see some RME hardware in the rack in the background!

In 1997, Matthias asked Stephan Flock to join the RME team. "Stephan studied music, has a degree as a balance engineer, and works for the famous Emil Berliner Studios, formerly part of Deutsche Grammophon — now Universal — as a freelance engineer. He has made numerous classical recordings all over the world, and has been responsible for the RME ADI8 Pro and DS, the ADI4 DD, the ADI2, the ADI648 and the TDIF Expansion Board, as well as lots of forthcoming RME products!

"At the time Stephan joined us, we had digital interface cards with ADAT ports, but we had no A-D or D-A converters, so I asked Stephan if he would be interested in designing the digital part of an eight-channel A-D/D-A converter with me doing all the analogue circuits, the layout and the artwork. We came up with a concept for a flexible eight-channel analogue-to-TDIF and ADAT converter which was announced at the Frankfurt Music fair in March 1998 — to almost no reaction from our dealers! However, we simply couldn't believe that such a unit would not sell, and at the end of 1998 we continued working on the ADI8 Pro. The unit began shipping in May 1999, shortly after the following Frankfurt Music fair, and proved to be a good example of how wrong dealers can be; it became a major success and a top seller for RME. Our Hammerfall DIGI9652 shipped in July 1999, and Steinberg were so impressed with our cards that they made OEM versions available via Steinberg distributors worldwide as part of the Nuendo series. However, we now sell our products only under the RME name."

MADI

RME have also made use of the MADI (Multitrack Audio Digital Interface) protocol first developed as a high-end data pipeline between digital multitrack recorders and digital consoles. Matthias Carstens: "At the end of 2002, we made a decision to utilise the MADI digital interface in our products, and in early 2004, our Mac OS X drivers turned the Hammerfall DSP MADI into the world's only MADI solution for Macs." (See the SOS March 2005 review.)

RME's Hammerfall DSP MADI card, combined with the ADI648 MADI-to-ADAT converter, makes for a powerful I/O system capable of handling up to 64 simultaneous channels.RME's Hammerfall DSP MADI card, combined with the ADI648 MADI-to-ADAT converter, makes for a powerful I/O system capable of handling up to 64 simultaneous channels.

While other companies are trying to establish new protocols such as mLAN, MADI already exists, it is a standard and it works — and RME have designed a MADI interface that is both affordable and reliable.

A single MADI PCI card can handle 64 channels of simultaneous 24-bit inputs and outputs at 'normal' sample rates and proportionally fewer at the more 'exotic' sample rates. The MADI data can travel long distances (two to three hundred metres) over a pair of optical or co-axial cables and RME also build the ADI648, a 64-channel ADAT-to-MADI converter unit that makes an ideal partner for up to eight of the company's eight-channel mic preamps (which have ADAT outs). Indeed, Stephan Flock used exactly this system for his latest operatic recording project, where he crammed a complete 64-channel, computer-based recording system into a single flightcase. Other customers have realised the benefits of MADI for replacing stage multicores, which means the RME design team now needs to think about remotely controlled mic preamps to add to its line.

RME's Hammerfall DSP MADI card.RME's Hammerfall DSP MADI card.

Steady Clock

RME's Steady Clock system is another very interesting piece of RME technology, reducing jitter when an RME interface fitted with the technology is clocked from an external source. Jitter is the name for any modulation of or variation in the master clock frequency. It has the effect of modulating the audio in much the same way as FM synthesis (albeit to a much lesser degree), introducing artifacts such as noise, enharmonic distortions and a deterioration of the stereo image. Traditional studio equipment uses a piece of circuitry known as a phase-locked loop to follow external clock signals, but there are two contradicting design requirements that lead to problems. Phase-locked loops need to track quickly in order to stay locked to the master clock, but they also need to track slowly in order to avoid adding high-frequency jitter of their own to the clock signal! In other words, their final performance is a compromise between how well they track and how low their jitter is. In practice, a standard PLL effectively removes jitter noise in the range above 100kHz.

RME's approach is to use a direct digital clock or DDC. These circuits still use a highly stable crystal oscillator as a reference, but they derive their output frequency from this digitally. "Steady Clock was originally developed to recover a stable and clean clock from the inherently heavily jittery MADI data signal", says Matthias Carstens. "The embedded MADI clock suffers from about 80 nanoseconds of jitter, caused by the time resolution of 125MHz within the format. Using the Steady Clock circuitry, the input jitter of 80 nanoseconds is reduced to less than two nanoseconds. Interface jitter values in real-world applications are usually below 10ns, so 2ns is a very good specification."Martin Björnsen, developer of the renowned Hammerfall hardware.Martin Björnsen, developer of the renowned Hammerfall hardware.

Of course, a DDS itself jitters, as it generates fixed step sizes between frequencies, so a DDS generator needs a filter on its output signal. Furthermore, the reference clock has to be measured with very high accuracy, or the errors of this measurement will contribute to the newly generated clock as additional jitter. RME's solution is simple but cost-efficient. Built around the Field-programmable Gate Array (FGPA) chip that lies at the heart of all RME's recent products, Steady Clock scans the input signal at 100MHz. This scanned frequency is then averaged over 1024 samples, which is equivalent to a digital jitter filter with a corner frequency of around 100Hz, reducing all jitter in the audio band. According to Stephan Flock, at 2.4kHz the jitter reduction is higher than 30dB, and even an input jitter of 50 nanoseconds vanishes below the inherent jitter of the Steady Clock, which is below two nanoseconds. Additionally, Stephan claims that the averaging process improves the already precise scanning of the input frequency.

Matthias Carstens: "Our DDS implementation operates at 200MHz, outperforming expensive, specialist DDS chips. A digital PLL then allows us to control the lock and sync behaviour completely, optimising it in a way that would not be possible with discrete solutions. The Steady Clock output signal has only a small amount of jitter, and can be easily filtered by a simple analogue high-performance PLL.

"The practical outcome is that we lock faster to any input signal than all our competitors do, we stay locked even when fiddling around with the pitch of an ADAT recorder — none of our competitors can do this — and we have no transition during the complete lock and sync process. Steady Clock is also the only system that operates steplessly over the whole sample rate range of 28kHz to 55kHz, without missing any frequencies or switching between several 'ranges'." Sure enough, measurement plots of RME's jitter compared with that of other high-end products shows it to be significantly less when externally clocked (only in such cases do the benefits of Steady Clock apply). What's more, as Stephan Flock explained, if the input clock drops out for any reason, Steady Clock will continue to generate a clock at the last valid frequency until the clock is detected again.

Matthias Carstens sums the technology up thus: "In short, Steady Clock guarantees low-jitter performance in all clock modes as its highly efficient jitter suppression cleans up any clock signal, and provides it as reference clock at the word clock output. This allows the best A-D and D-A conversion to be achieved, no matter what the reference clock source." For more information on Steady Clock, check out www.rme-audio.com/english/techinfo/steadyclock.htm.

Same Difference?

Today, RME has more products than ever, but the core team of designers remains the same, with Ingenieurbüro Müller manufacturing and Synthax distributing worldwide, and Matthias Carstens thinks this stability is a decisive factor in their success. "RME always has been and still is a group of developers with me as head. The secret of the company is in the core team's qualifications. You can hire engineers who can do electronics. You can hire project guys who studied economics. You might even hire musicians. But you won't get the same result as you do when the core team has all these abilities already."

Leaders In The Field

The RME Fireface 800 has an updatable Field Programmable Gate Array (or FGPA) chip at its heart, like the recent MADI-enabled Hammerfall card.The RME Fireface 800 has an updatable Field Programmable Gate Array (or FGPA) chip at its heart, like the recent MADI-enabled Hammerfall card.

RME's Fireface 800, as its name suggests, can exploit the higher speed of Firewire 800 and this has been achieved by the use of a Field-programmable Gate Array (or FPGA) chip that has been programmed to function as a Firewire interface. According to Stephan Flock, RME took this approach partly because existing Firewire 800 chip sets were not entirely suitable for audio use, and also because the use of FPGAs allows the units in which they are installed, in effect, to be given a hardware update as improvements are made to the design.

So far, this approach has stood RME in good stead. Early iterations of the Fireface 800 had compatibility issues with some commercial Firewire equipment because of operational quirks in the chip sets used in these products. Subsequent updates have enabled them to iron out these problems, whereas if they'd used commercial Firewire chips, there would have been no way of updating the designs. The FPGA chip used by RME also has a powerful onboard DSP section enabling the designers to add the Total Mix feature. This allows you to set up multiple independent monitor mixes, and also means units fitted with the chip can function as a stand-alone mixer without depending on the computer.

Published July 2005