Discover Eisenberg's new four unit software synthesizer.
Learn about the story behind the development of VIER.

VIER- Behind the Scenes

by Gunnar Eisenberg

Is the Doepfer MS-404 just a Roland TB-303 clone?

The Doepfer MS-404 is a monophonic analogue synthesizer with extraordinary, aggressive modulation sounds that are grounded in the two LFOs that reach far into the audible frequency range. These sounds are sometimes very guttural, screaming or dissonant and have newfound popularity in Dubstep, Indie Rock or Crossover.

The MS-404 was released in the mid-nineties in an era when analogue sounds experienced a renaissance. Back then a huge number of hardware clones of the legendary Roland TB-303 were available on the market. However, when comparing the feature sets of the TB-303 and the MS-404, it quickly becomes apparent that fewer similarities exist than the names would imply. The functionality of the MS-404 with the two modulation LFOs, the full ADSR envelope, and frequency tracking is significantly larger than that of the TB-303. The waveforms of the MS-404 have a shape that is much closer to the exact mathematical form, while those of the TB-303 are quite deformed from the outset.

During the early conceptual design of VIER. 

Furthermore, the 24dB lowpass filter of the MS-404 uses a classic Moog transistor cascade, in which the resonance easily extends to the self-oscillation, whereas the TB-303 uses a diode cascade as a 24dB lowpass filter without self-oscillation. The diode cascade’s filter roll-off is significantly flatter around the cutoff frequency compared to the transistor cascade’s filter roll-off. The diode cascade filter is therefore often mistakenly referred to as an 18dB lowpass filter, because the roll-off in the audible range is so flat.

Motivation for developing VIER

During the mid-nineties, the Berlin club scene was flooded with pure, minimalist electronic music. The sound aesthetic was greatly determined by analog sound synthesis, because impressive results were achieved with very small setups. A simple VCO/VCF/VCA configuration, as the MS-404 is based on, can easily carry and shape entire tracks. Analog sound synthesis is much like cooking. If the individual ingredients are of high quality, only a few ingredients are needed to achieve a tasty result.

The idea for VIER originates from the desire to play four MS-404s in a rack with a MIDI dispatcher, so as to realize four-note chords. Due to costly hardware prices back then, this setup could only be realized with an appropriate financial budget. Since then, the processing power of modern computers and the available DSP algorithms has greatly developed. This concept can now be implemented as a plugin with top-notch sound quality. In this context, VIER expands the original concept with some innovative features such as the parameter linking, the voice management, and convenient modern features such as automation, and a preset browser.

One of the early VIER alpha versions comes to life.

According to our paradigm "We do the Math - You do the Music," the conceptual design’s focus of VIER lies on an intuitive, easy operation without restricting the musical possibilities. A good synthesizer should feel like a versatile tool for the musician and at the same time be handy to use, so that the user can get into a flow with the device. With VIER we wanted to introduce something complementary to Einklang but expand the maximum versatile sound range. While Einklang is especially very powerful in the field of pads and drones, VIER adds distinctive and screaming basses and leads.

Development Process

Before the start of Eisenberg, my colleague Dennis and I had been working for many years as DSP developers for the market leader of software synthesizers. Dennis had modeled a lot of guitar amps and guitar effects; so analog modeling is a well-known field for us. For VIER, we gathered different hardware units of the MS-404 revisions and started researching the internals.

The MS-404 has a well documented and very tidy, robust circuit design in which operational amplifier circuits decouple the individual sound components from each other. This also contributes significantly to the cold techy sound impression of the MS-404, since the components can’t interfere with each other in a negative way. In addition, this separation allows the extreme LFO modulation effects to be produced precisely and screaming, not washed out.

Three different revisions of the MS-404 in comparison.

The four revisions of the MS-404 differ slightly in their circuit design and the built-in types of potentiometers, but sonically they are quite similar. A unit of the final series served as our reference model for the implementation. We approximated this unit sonically and have formed some phonetic averages with the units from the earlier series.

For the analysis of the individual function blocks, small measuring circuits were built in order to uncouple the relevant signals from the rest of the circuit. For the measurements, a plurality of signals in a wide variety of settings has been recorded. The analysis of these signals was carried out partly with the aid of AIST, which is also used in Einklang’s analysis and resynthesis engine. In a fairly long process, we were able to uncover the secrets of the MS-404 and transfer every detail to our synthesis model.

A MS-404 hooked up to one of our self cooked measuring circuit boards. 

In addition to the precise reproduction of the critical characteristics and nonlinearities, special attention laid naturally on the core elements of the MS-404, that is, the filter and the two LFOs. For this purpose we relied on technologies that are also found in other high-quality analog emulations. Therefore, we use e.g. zero-delay-feedback filters and aliasing-reduced oscillators. Both were necessary because otherwise we would not have succeeded in reproducing the extremely high LFO modulations.

During the analysis of the MS-404, we found some points where organic overdrives can be perfectly added. This allows achieving sound effects that go beyond physical limitations of real analog hardware and push the natural non-linearity to the extreme. We provide a cumulative (over-) drive with only one knob in these three points:

  • Behind the VCO, distorting the waveform,
  • Within (!) the filter’s transistor cascade, resulting in a distorted frequency response and a dying resonance, and
  • Inside the VCA, distorting the output by the shape of the VCA.

Dennis performing one of probably ten billion listening tests :-) 

During the development process we continuously performed comparison tests between the hardware and our model. This was carried out in blind tests with our emulation together with the different hardware units of each revision. The aim of these fine-tuning listening sessions was that one could no longer distinguish the originals from our model.


Many thanks to Dieter Döpfer and Doepfer Musikelektronik GmbH for allowing us to call the MS-404 by its original name and for allowing us to build VIER both sonically and visually close to the original. You can find more information on Doepfer and the MS-404 on their website:

MS-404 Monophonic Analog Synthesizer