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Recording is Changing

Rudiger Forse

Stefan Fischer

Marketing Director Stefan Fischer interviews
Product Manager RŁdiger Forse about the MindPrint DTC


In the digital age, achieving a new level of quality is something that is nearly impossible to do with just higher sampling rates or bit depths. Digital processing quality is better than ever, and has reached a level that meets even the highest sonic and dynamic requirements. With a sampling rate of 96 kHz we can reproduce frequencies that are more than double the highest frequencies manís hearing mechanism is capable of perceiving. A resolution of 24 bits offers us a dynamic range that can capture sound at pressure levels that go far beyond the threshold of pain of human hearing. In the past, our attempt to reproduce all the perceptible nuances of a sound was severely limited by the available technology; today we are much closer to capturing all the details of a sound in its full glory.


The mission of the DTC

Q: Since digital technology today is capable of such high resolution, one would think that the best and shortest connection would be a pure analog-to-digital converter. So why is MindPrint developing high-end analog technology?

A: Whatís even more important than the recording quality and reproduction quality of the digital converter itself is the quality of the analog circuitry preceding the converter. Today the only part of the signal chain that is subject to loss is the analog section that prepares the signal right before it hits the digital realm. The task of the DTC is to make this part of the path as good and as short as possible.

Q: This can in fact be done, canít it, without additional components in the signal chain?

A: Yes, this is easy to imagine. We already have digital microphones, and guitars with digital pickups wonít be far behind. Thank God, it would be the end of analog cabling.

Q: Öand the beginning of synchronization chaos.

A: True. Besides, there are different instruments, microphones, and other things that people will continue to want to use. A Neumann U47 tube mic, for example, doesnít have a digital output. Youíve got to keep in mind: the sound of instruments and microphones occur in the analog realm, as waves and current, and not as bits and samples. And waves and current are very sensitive as to how they react to physical quantities such as impedance, capacitance, and induction. And only when we pay proper attention to these quantities, and waves and current are turned into the "right form," do we stand a good chance of performing a proper conversion to digital.

Q: By "right form" do you mean the processing of the frequencies and dynamics?

A: Yes, that too. Good sound starts well before the processing, in the input stage itself. Technically speaking, the job of the DTC is to take a very weak modulating electrical signal with a very broad frequency range and amplify it and "shape" it. But this electrical signal has its own peculiarities: depending on whether the induction and the capacitance is set up in the circuit to run in parallel or in series, these can have a dampening effect on the bass and treble. With all analog sound sources, whether pickup or microphone, or even a normal cable, the capacitance and inductance play a role and influence the sound. The special input circuitry of the DTC respects them in a very special way, so that they do have the necessary "raw form" required for the subsequent frequency and dynamics processing.

The preamplifier

Q: The microphone input of the DTC includes a transformer. Technically, transformers alter the sound. As the noise quotient of analog signal sources has constantly improved, we were happy that we no longer needed to use a transformer. Why the step backwards now?

A: Itís not a step backwards, on the contrary. The complex interplay of impedance, capacitance and induction in the input transformer is responsible for the optimal matching of the microphoneís diaphragm to its electronics, and aids considerably in enabling the microphone to reproduce sound in a natural manner. MindPrint has researched these phenomena and collaborated with the company Hauffe to develop a new transformer. This sophisticated transformer possesses the advantageous sound characteristics known from older models, but avoids their common side effects, such as phase distortion in the treble region, because it has such an extremely broad frequency range (up to 100 kHz) that the phase distortion occurs out of the range of human hearing. Furthermore, because it has a turns ratio of 1:5 the transformer makes life easier for the subsequent amplifier stage, thereby reduces distortion and makes it possible to achieve an extremely good signal-to-noise ratio.

Q: One thing that struck me about the DTC is the impedance of the microphone input. At 5 kOhms it is considerably higher than usual with microphone preamps. Why does MindPrint deviate so greatly from the 600-Ohm standard?

A: Quite simply, it sounds better!

Q: Of course. Can you go into greater detail?

A: Certainly, but weíll have to get fairly theoretical: as we already discussed, the impedance of microphones is not a constant but is frequency dependent. Within the frequency range of microphones certain there exist certain impedance peaks which can far exceed 1000 Ohms. If the input impedance of a microphone preamp is less, these peaks are damped, which in effect automatically changes the frequency response. Since these peaks occur especially in the treble region, the automatic damping of low-impedance preamps leads to a loss of brilliance. The DTC, due to its high-impedance design, can handle even extreme peaks and thereby avoids losses in the highs. This especially makes dynamic microphones sound more transparent and natural. Condenser microphones also sound better, since their amplifiers, which are not loaded down as much, can operate with less distortion. Finally, since the highs are reproduced better, less equalization is needed.

The equalizer

Q: Letís talk about equalization here for a moment. What makes the EQ of the DTC special is the parallel arrangement of the filters. Not everyone is familiar with the technical difference. Can you give a brief explanation here?

A: Sure. Normally, filters are placed in the circuit one after another. In doing so, the complete frequency spectrum of the signals goes through all the filter stages, which can lead to a considerable degradation of the signal quality. You can think of this like a winding, one-lane road that slows down the signal. In contrast, the equalizer of the DTC uses parallel filters, so that the signal is divided into all four bands at the same time. Like a straight four-lane Autobahn, on which the signal moves ahead without any obstructions.

Q: Sounds logical. But thereís still the issue of the passive nature of how the original signal is handled. Whatís that all about?

A: The original signal goes through the EQ practically like through a thick cable, without interruption. The bands of EQ, which are laid out parallel to the original signal, only operate on those frequencies that are to be processed. If a frequency range is to get a boost, it will be mixed into the original signal in phase, and if cut, with phase reversed. But the original signal remains. This way, you maintain optimum fidelity to the original signal.

Q: The treble band and the bass band are set up as shelving filters, whereas both mid bands are laid out as bell filters. An adjustable Q control, common with bell-shaped filters, is uncommon with shelving filters. How are we to understand a "bandwidth" with shelving filters?

A: Thatís right, a Q-factor control is quite uncommon with shelving filters, although it adds considerably to the sonic flexibility. High Q-factor settings in the case of boosting will at first produce a slight dip in the middle frequency range before the curve rises to the edges.

Q: So, before the bell there is first a dip?

A: You can think of it like this: if you want to boost the highs above 10 kHz, for example when mastering, you can shape the curve in such a way that the frequency range before it, from 8 to 10 kHz, is cut. This will result in a supremely soft sound. Or you can boost the low bass without having to worry about ending up with mud between 150 ad 300 Hertz. When cutting instead of boosting, the effect is just the opposite: at first there is a boost, and only then a cut. The good thing about it is that this can be adjusted with infinite variation. This gives you a lot of control, so much so that you often donít even need to use the mid controls. The applications are really very flexible and lead to astonishing sonic results.

The dynamic section

Q: The compressor/limiter is also supposed to be capable of astonishing results, I understand. But it has only two controls, correct?

A: Thatís right, all the filters together have a total of 14 controls per channel. The compressor has only two, plus one switch. The first control very effectively combines threshold and ratio, while the second adjusts the times, and the filter switch replaces a side-chain EQ. In other words, all parameters are covered.

Q: And how does this work in practice?

A: The compressor/limiter control functions in a way that is quite effective: When turned completely counterclockwise all that happens is that there is a mild compression of the loudest signal peaks. The more you turn the control clockwise, the lower you set the threshold. In the controlís middle position, "Limit @ 0dBfs," the channel will be dependably kept from being overdriven. All signals are brick-wall limited at 0 dB. Thatís something that you absolutely want with digital recording. At the same time with this setting, soft signals are amplified considerably. The more you turn the control clockwise, this amplification becomes greater, while the limiting function stays the same.

Q: So, the more I turn this setting up, the fatter the sound I get?

A: Yes, and at the same time it gets brick-wall limiting. Ordinarily you would need to make further adjustments to Threshold, Ratio and Make-Up Gain, and still send this signal through a limiter. The DTC takes care of this by itself.

Q: And the control times?

A: The Release control determines when the compressor will again raise a soft signal after having reduced a loud signal. If you design it so that it responds too quickly, you might overemphasize reverb trails, for example, which would overly thicken the sound. With longer release times, more of the character of the original signal is preserved. The attack is not changed, thatís something which is handled by the Adaptive Response feature.

Q: What exactly is Adaptive Response?

A: Our big secret! But the basic principle is easy to imagine: Adaptive Response operates with several control times which are mutually interdependent. A standard compressor will kick in, for example, when signal peaks appear in material that is already fairly dense, and you will hear pumping. Here thereís an addition controlling function kicks in which handles fast transients, independently of the basic setting.

Q: But I thought the filter was supposed to prevent pumping.

A: Exactly. But pumping can occur when bass-heavy signals affect the sensors too strongly. Typical scenario: the bass drum causes the highs to be reduced. For this reason the filter was set up in such a way as to make the compressor less sensitive to low frequencies, resulting in a type of compression that corresponds much more closely to the way the human ear actually works. Since we are modeling a natural function of human hearing, this filter circuitry improves practically every signal thrown at it.

Q: Exactly what role do the opto-couplers and the tubes perform here?

A: Both of them do what they do best: the opto-coupler compresses in a very unobtrusive and pleasing way. Since an opto-coupler is a passive component, it sounds substantially cleaner than an active semi-conductor circuit. The tube with its natural form of saturation reliably handles the limiter function, and is naturally responsible for the harmonic overtones.

Q: With hard limiting at 0 dB, is the sound similar to that of a brick-wall limiter?

A: No, not at all. The limiter in the DTC doesnít slam the signal against the wall, on the contrary. The compressor function turns into a limiting function very gradually, i.e. soft-knee. The sound that results is comparable to that of large-head analog tape machines. Thanks to the added overtones, compressed signals are more perceptible to the human ear, so they are experienced as if they were louder than they actually are.

Q: How does the DTC do this?

A: With the DTC, the tube circuitry is tweaked in such a way as to emphasize the uneven overtones and minimize the even ones.

Q: ...in other words, the octaves are not emphasized, while the fifths and the thirds are?

A: Exactly, and that results in a very pleasing, unobtrusive sound. The human ear simply likes it more when signal peaks make themselves heard in the form of added presence rather than increased volume.

Analog and digital outputs

Q: The Output control is at the end of the signal chain. What can you tell me about this?

A: At a position of 0 the optional digital converter is driven to its optimal level. If you limit to 0 dB full-scale, the dynamics of the converter is used to optimum advantage.

Q: So, you mean maximum level together with prevention of overs?

A: Yes, however to play it safe, you still shouldnít run critical material as hot as 0 dB, even with full-scale limiting. The best way to monitor it is to keep an eye on the input meter in the recording software you are using. But you can also see it in the display of the DTC. 

The digital option DI-MOD 24/96

Q: The digital converter operates with 24 bits and at 96 kHz. The spec sheets says that weíre dealing with a dynamic range of 113 dB (A). But there are other converters that go higher, arenít there?

A: The converter chip itself will do more. In any case today practically all the manufacturers of converters - is the manufacturers of hardware built around the converter chip - tend to use the same model of chip. All the same, the finished products both sound different and have a different dynamic range, because itís not just the chip that determines the quality, itís the entire analog circuitry built around it, the filters, the signal paths, and other factors. You can, of course, design the circuitry around the chip in such a way as to absolutely optimize the dynamic range, but those measures will take a toll on the sound. Maybe not measurably, but audibly!

Q: So, very good specs donít automatically guarantee that the conversion will also be very good.

A: That would be great, wouldnít it! Think about the good old CD standard. Thereís a world of difference in sound between cheap CD players and expensive high-end units. The same thing goes for AD converters. Even when they have similar technical specifications and test results.

Q: What kind of digital interface does the digital module use?

A: With S/P-DIF it uses an optical interface in TOSlink format, and an electronic one on coaxial RCA connectors, with AES/EBU available as an option. A great feature of this module is the Auto/Master switch, which forces the DI-Mod into Master mode at the selected sampling rate, regardless of the sampling rate of the incoming signal.

Q: So the AD converter operates completely independently of the DA converter?

A: Thatís right. For example, you can process 44.1 kHz recordings with the DTC and convert them to 96 kHz. Or you can do it the other way around, for example starting with 96 kHz material from a project you might be mastering with the help of the DTC, and convert it to the right sampling rate to press the CD. Originally this feature was conceived just as a way to avoid the stress of synchronization problems, but in practice it has turned out to be quite handy. Another very useful feature is the stereo DA output of the DI-Mod. In other words, with the DTC and the installed digital option you can operate completely self-sufficiently.

Q: Does that mean that the DI-Mod can be used to monitor the digital output signal of a computer-based digital audio workstation?

A: For example, yes. Just think about the direct connection to any Apple computers as they also feature optical digital in/out.

The DTC concept

Q: OK. That brings us to the end of the signal chain. To sum up, then, what is the DTC?

A: The DTC is a front end with a unique combination of tried-and-true analog components together with the sonic authenticity of todayís most advanced circuit designs. The best of both analog and digital worlds in a single unit, yet with the same type of extraordinary value that MindPrint is known for.

Q: With what other units could it be compared?

A: The original idea behind the design of the DTC was the all-in-one channel strip. The DTC is different from other existing designs in that it is affordable and will make the expensive sound of esoteric outboard units available to every project studio owner who wants extraordinary sound. Since it is the only unit with this sound quality and combination of features in its price class, itís hard to make comparisons. Furthermore, it is a two-channel device, whereas most channel strips are only single-channel.

Q: One channel is often enough, so why two?

A: Man has two ears. (smiles) No, the whole point of the DTC is simply to offer a comprehensive solution. A single channel only goes half-way. After all, when you record, you not only want to record solo guitar or voice; you might want to record a choir in stereo, or take a stereo feed from a keyboard and submix. Furthermore, the DTC is a superb mastering tool and can also be seen in live racks.

The benefits

Q: At a price of about 2000 Euros, the DTC is not exactly something youíd decide to buy while youíre waiting in the checkout line at the store. For whom exactly did you design the DTC?

A: For every project studio. Recording is constantly expanding and changing for the better. But most musicians still use cheap preamps, mediocre equalizers and ineffective compressors that definitely degrade the signal. It is important to realize that a high-quality microphone needs an input channel of similarly high quality, or its value is lost and its quality degraded. If the preamp stage and the analog signal processing are crappy, then no software in the world, no matter how good, are going to be able to restore the tone and expressiveness of a particular voice. The DTC meets the needs of high-end studios and fulfills the dream of every project studio owner.

Q: Like Alesis did when it came out with the ADAT and made high-quality 8-track recording affordableÖ.

A: Exactly! Suddenly, professional multi-track recording quality was no longer reserved exclusively for the well-to-do. The ADAT started a revolution; you might even call the ADAT the "mother of all project studios."

Q: It was the solution for thousands of musicians. The unit itself actually cost quite a bit, but what you got for your money was extraordinary for the time.

A: The DTC is quite a similar story. It is the equivalent of a classic high-end outboard rack, but with such features and at such a price that itís a perfect fit for the project studio.

Q: So would you say that the DTC is intended for everyone who is looking to upgrade his digital equipment?

A: Thatís a good way of putting it. And it would be an upgrade that would last a lifetime, because unlike digital, the analog technology in the DTC will never be outdated. Plenty of musicians are excited about existing high-end analog units, but their price scares them away; or in the case of vintage units, they may not even be available any more. The DTC will make high-end recording accessible and affordable, plus its quality will appeal to anyone seeking a dedicated preamp, EQ, or compressor. Because it is such an outstanding value, it is a real alternative to many of the expensive analog outboard units. For those looking for exceptional - yet affordable - recording quality, the DTC is the logical answer. The ultimate instrument for every ambitious musician who takes recording seriously.