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Mindprint Envoice MkII

Valve Recording Channel By Hugh Robjohns

Mindprint Envoice MkIIPhoto: Mike Cameron

Mindprint have overhauled the electronics in their popular valve recording channel, and have also added extra facilities and an optional USB recording and monitoring interface.

The original Mindprint Envoice — the first product from this German manufacturer — was launched at the end of 1998 and I reviewed it for Sound On Sound readers in the September 1999 issue. Since then it has become a firm favourite in the affordable voice-channel market, providing a good range of well-designed sound-shaping facilities (including mic, line and DI inputs, three-band EQ, compressor and a valve stage), and with fine quality.

Photos: Mike Cameron

So if the original was so good, why release an updated MkII version? The answer lies in Mindprint's constant striving for maximum performance at a given price, combined with feedback from users' wish lists, and changes in the way people tend to work these days. One of the most significant changes has been to the optional digital interface module. The original could be equipped with an S/PDIF interface, but increasingly customers have been asking for a USB port to enable the Envoice to be plugged straight into a computer.

The new MkII version, launched a few months ago at NAMM, retains the same overall structure as the original, with identical input, EQ and compressor facilities, but it also adds an optional new USB interface, a completely redesigned preamp section, a new balanced insert facility, improvements to the circuitry of the EQ and compressor sections, and a better power supply. The front-panel layout and legends have also been improved, and the rack ears can be detached for tabletop applications.

Back & Top Panels

The Envoice MkII is a 1U rackmount unit, although the ears can be easily removed as mentioned above. The front panel is constructed from a thick transparent plastic strip, with the legends on the reverse surface to protect them, while the rest of the case is made of traditional black-painted steel and measures approximately 220mm from front to back. Moving around to the rear of the unit, the microphone input is connected via an XLR, while a second XLR and a TRS socket cater for a balanced line input. A further pair of TRS sockets provide balanced insert send and receive connections, and, finally, the main output is accessed on both an XLR and another TRS socket. These are wired in parallel, so plugging an unbalanced connector to the TRS output will unbalance the XLR output too.

Mindprint Envoice MkIIPhoto: Mike CameronI'll skip over the optional USB module for now — see the 'Optional DI-Mod USB Interface' box for more information. The final rear-panel facilities comprise a grey button which provides an earth-lift facility to help alleviate ground loops, and the mains inlet IEC socket. The MkII Envoice employs an internal switched-mode power supply which not only means it can operate on any mains supply between 90 and 264 Volts, but also that the anode supply voltage for the valve is very tightly controlled, resulting in a more consistent sound quality. The unit draws 45W of power.

For desktop users, the top panel replicates the rear-panel analogue connection markings, making it easier to plug the unit up when leaning over from the front. There is also a large schematic of the signal path through the unit and a list reminding the user of the eight preset compressor modes, of which more below. This schematic is strangely not included in the handbook, but it's not entirely accurate anyway.

Controls & Facilities

The front-panel controls are laid out logically enough, but the plastic knobs do feel a little cramped. The line-level input gain, EQ cut/boost controls, and the output fader all have centre detents for the unity-gain position, and every control has well-calibrated markings which make recording and resetting control positions very easy. Most switch functions are provided via clear buttons which illuminate brightly in blue when pressed. Additionally, there are three miniature toggle switches in the input preamp section, and a black lever toggle for the mains power.

Starting from the left-hand side of the panel, an LED bar-graph with an associated button shows either the input or output signal level. The meter is calibrated from -20dBFS to 0dBFS, the latter being the overload point of the optional DI-Mod interface. An unbalanced 470kΩ instrument input socket occupies the bottom left-hand corner, and plugging a connector in automatically routes this DI signal through the line input circuitry. The line/DI input level control spans the range from fully off to +22dB, and an adjacent toggle switch selects mic, DI/line, or digital input — the last derived from the DI-Mod interface if installed. The line input circuitry can accommodate a maximum input level of +20dBu, which is a little lower than most high-end equipment, but should prove adequate in home studios.

The microphone input has a relatively high impedance (either 5kΩ or 10kΩ depending on which bit of the spec sheet and handbook you choose to believe) and can accommodate signals up to +25dBu if the 20dB pad is switched in. The advantage associated with a higher microphone input impedance is that it tends to be a brighter (arguably less damped) sound, particularly from dynamic microphones. A continuously variable gain control spans 19-75dB of gain, and phantom power can be provided via the last toggle switch. An LED to indicate the presence of phantom power would have been useful, but that is a minor niggle.

The final preamp facility is a simple high-pass filter selected with an illuminated button. This provides a 12dB/octave roll-off below 80Hz, and is ideal for reducing the rumble from mechanical vibrations reaching a microphone. The original Envoice had two switchable turnover frequencies, but at 50Hz or 100Hz these were often too low or too high. This fixed 80Hz solution seems more practical to me.

Optional DI-Mod USB Interface

The new optional digital interface is called the DI-Mod USB, and it is physically compatible with previous Mindprint interface modules such as the DI-Mod 24/48 and DI-Mod 24/96, provided that the host product supports the functionality of the new interface. Installation is as simple as removing the lid of the host processor and the blank cover panel, inserting the module, and plugging a short ribbon cable into a dedicated socket. Once installed, the unit provides both an S/PDIF output and a bi-directional USB interface. The latter is the usual square USB socket and operates using the USB 1 protocol. Given that the port only carries two pairs of channels in each direction with a maximum of 24-bit/96kHz resolution, Mindprint elected to stick with the universally known USB 1, rather than the faster USB 2.

Suitable ASIO drivers for Windows (98, 2000 and XP) and Mac (OS 9 and OS X) are supplied on a CD-ROM, although as you would expect the company's web site carries the latest versions (current v2.23 for all formats). The driver software is used to determine the sample rate and word length of the USB output, as well as the signal carried on the S/PDIF output. When an active USB connection has been detected, a Sync LED illuminates on the rear panel.

There are two basic software-controlled operating modes for the S/PDIF output. The first is for it to carry the Envoice output (on both channels) via the A-D converter in the USB module, while the second is for it to carry the returned USB stereo monitoring signal. The S/PDIF output is provided on a phono socket, but as this is set back almost flush with the panel the use of some of the more chunky phono connectors is precluded. The sampling rate and signal provided by the S/PDIF outlet is determined by the USB driver, as mentioned above, but if the product is used in a stand-alone mode (ie. without a USB connection to a computer) the S/PDIF interface operates with the previously selected word length, sample rate and source.

Also on the rear of the USB interface is a TRS socket and a button. The button selects one of two operating modes for the socket, which can act as either input or output! In the Stereo output mode, the TRS socket carries an unbalanced stereo USB monitoring signal output, via the D-A in the interface, with left on the tip and right on the ring. Although without a volume control and not designed to drive headphones, I found this a useful facility all the same.

Apparently, the USB drivers are the same as those used by Apogee and Digidesign, and are claimed to be the fastest available. Although latency through the USB interface is very low — typically 3ms for the input and 4ms for the output — there may be occasions where the inherent processing delay causes problems. Mindprint have addressed this with a Direct Monitoring mode. Selected through the driver software again, this feature mixes the Envoice output signal (ie. the A-D input) with the USB monitoring return signal, and routes the combination directly to the TRS output socket for real-time monitoring.

When switched to the alternative Insert mode, the socket can be used to input an external analogue signal to the A-D converter, and thus into the USB and S/PDIF interfaces. When in this mode, the Envoice's internal signal is routed to the right-hand channel of the converter, while the external input is routed to the left-hand channel. The tip connection carries the unbalanced input, while the ring connection carries the channel-one output, if required.

As far as technical specifications are concerned, the converters are claimed to accommodate any sampling frequency between 32kHz and 105kHz (32-96kHz in practical terms), and provide 110dB dynamic range ('A' weighted). While the S/PDIF interface complies with all the usual standards, the unbalanced analogue connections have a restricted maximum level of approximately +15dBu, which is a little low in comparison with most professional equipment. However, as a monitoring signal output, I think the restricted peak level is unlikely to present much of a problem in practice.

Signal Processing

The equaliser is a simple three-band affair, operationally identical to the original, and it is clear that considerable thought and care has gone into choosing the parameters to make it as flexible and musical as possible. Whereas most three-band units would provide shelf equalisers for the top and bottom bands, with a bell-shaped mid-range section, the Envoice is provided with three bell sections, each of which can be switched into circuit independently.

The LF band can be tuned over the range 20-300Hz with ±15dB of cut or boost. However, the curves are not symmetrical — the bandwidth of the boost side is much larger than that of the cut side. The filter has a broad 6dB/octave slope in boost, but a much narrower 12dB/octave slope when cutting. This asymmetrical design is not unique, but is very effective, as it allows creative warm boosts to be applied, or resonant tones to be reduced with almost surgical precision. Furthermore, by tuning the centre frequency to 20Hz, the equaliser takes on the same response shape as a normal shelf EQ when boosting.

The mid-range section is equipped with a fully variable Q (bandwidth) control in addition to the gain and frequency controls. The centre frequency of the bell curve can be tuned between 100Hz and 11kHz — an unusually wide range — and the same ±15dB of boost or cut can be applied. The boost and cut curves are symmetrical, but the Q (bandwidth) can be varied between three and 0.15 (third octave to six octaves respectively). The HF section has a fixed Q and symmetrical boost and cut curves once again. The centre frequency can be tuned from 1.6kHz to 22kHz and the same ±15dB cut or boost applied. The filter slope is a traditional 6dB/octave, and if the frequency is turned all the way up this section also behaves like a standard shelf filter.

The compressor is broadly the same as the original design — using a solid-state VCA as the level-controlling device — but this stage has been enhanced with the addition of an eight-way rotary Compression Mode switch, of which more in a moment. A bar-graph gain-reduction meter indicates a 22dB range, with the first 8dB of attenuation shown in precise 1dB steps. Two illuminated buttons enable a 300Hz, 6dB/octave high-pass filter to be switched into the side-chain, and the compressor to be switched into circuit. The side-chain filter reduces the compressor's sensitivity to low-frequency signals, and thus the material is compressed more accurately based on the density of the mid-range instruments.

There are three rotary controls, and the first sets the amount of tube saturation. The original Envoice scaled this from one to eight, but the new model is marked with percentages from zero to 100 percent. Next is the Threshold control, with a +2dB to -28dB range, although it is unclear what the reference point is. The last control sets the Ratio from 1:1 up to infinity:1 (ie. limiting), and the first quarter of the rotation spans the delicate region below 2:1 — making it easy to set very subtle compression ratios.

The original Envoice had programme-controlled attack and release times, with a button to select ten times slower attack- and release-time constants. However, the MkII model has been made considerably more flexible, with the addition of an eight-way rotary switch which configures the compressor for a variety of applications. The attack and release times are still programme controlled, but their initial settings are determined by the mode control. There are three vocal settings, two for guitars, two for basses, and a percussion setting — and these preset not only the attack and release time constants, but also the tube saturation and ratio, and insert the side-chain filter as well.

This screenshot shows the ASIO settings for the supplied USB Audio driver.This screenshot shows the ASIO settings for the supplied USB Audio driver.Photo: Mike CameronThe presets offer a range of useful starting points, and the ratio and saturation controls can be adjusted further to optimise the effect as required. A table is provided in the handbook detailing the attack and release settings (short, medium or long), plus the initial saturation and ratio settings for each preset. For example, the 'fat analogue vocal' setting (V2) has a long attack with a short release, 50 percent tube saturation, a ratio of 3.5:1, and the side-chain filter on. The natural vocal setting (V3) employs a short attack with a medium release, 25 percent saturation, a 1.7:1 ratio, and the side-chain filter again.

The last control section is the output stage, and the facilities here are a total bypass button and an output fader which ranges between fully off to +8dB, with a unity-gain position at the centre detent. A tricolour LED next to the output level control indicates the degree of tube saturation. With almost inaudible amounts of saturation the LED is green, progressing to yellow with heavy saturation overtones, and red when the circuitry starts to overload. The remaining panel space is given over to the familiar Mindprint logo and transparent backlit (in blue) window which reveals the glow of the internal 12AX7 triode valve.

Sounding It Out

My initial experience of the Envoice MkII was disappointing. The mic input exhibited a degree of instability at modest gain settings around the 35dB mark, which manifested itself as jumps and modulations of the noise floor, as well as quiet but nonetheless obvious buzzes, fizzes, whistles and other unwanted noises. At gain settings above about 45dB the mic amp appeared to work satisfactorily, but still appeared a little noisy (the handbook does not supply an EIN figure). These symptoms are typical of an amplifier instability fault, and given the fine reputation Mindprint have acquired for its other products I suspected a rogue machine!

On contacting Mindprint it turned out that they had recently discovered the same problem and had tracked it down to a particular production batch of Envoice MkIIs. The production fault has now apparently been solved and any early machines like this review model will be repaired or replaced free of charge should you find yourself with one. When functioning correctly, the mic circuitry should be on a par with the other Mindprint products, but clearly if you are considering buying the Envoice MkII it would be worth checking the performance of the mic amp to confirm it is working properly. The serial number of the review machine is 20093173, so models with similar numbers should be tested carefully. We hope to receive a more recent production unit shortly to check the performance again, so keep an eye on the SOS News pages for an update on this.

Other than that, everything worked very well indeed. The line input is quiet and stable, the DI input effective, the equaliser is easy to adjust and sounds very musical, and the compressor is capable of delivering everything from 'very subtle and transparent' to 'hard and punchy'. The metering and illuminated buttons make it easy to see what is going on, as does the design of the control knobs. I found the close proximity of the rotary controls and the size of the knobs made the Envoice MkII a little fiddly to adjust, but it's easier if you pinch the top of the knobs rather than trying to grasp them around their bases.

One aspect I particularly like is that the tube saturation can be used without the need to compress the signal, simply by dialing the ratio back to 1:1. The provision of a side-chain high-pass filter is also very useful when compressing bass-heavy material — and it makes the compressor far less susceptible to plosive pops on vocal tracks, for example.

Like the original, the Envoice MkII is capable of very subtle warm sounds, with a very responsive compressor which excels at transparent compression and performs far better than most in this UK price range. The mic preamp production problem aside, this MkII version offers a very worthwhile improvement over the original, and the USB interface module makes a very attractive alternative to the existing S/PDIF modules. On my PC the drivers proved easy to load and configure, and the system worked very well indeed. The latency is certainly very low and the S/PDIF routing flexibility will prove an additional benefit to many. Overall then, a thumbs up for the Envoice MkII, which should be firmly attached to the short list if you are planning to add a voice channel to your equipment inventory.

Test Spec

Propagamma USB audio driver v2.23.
2MHz Pentium IV PC with 1GB RAM, running Windows XP Home.

Pros

  • Revised electronics throughout.
  • Improved interconnectivity and better PSU.
  • Musical EQ and transparent compressor.
  • Controllable valve saturation effect.
  • Optional digital modules now include USB interface.

Cons

  • Problems with the mic preamp in early production batch.
  • More congested control panel.

Summary

A well-equipped recording channel offering effective and musical processing at a very attractive price. The compressor is simply excellent and the valve saturation highly controllable. A versatile three-band EQ, flexible I/O facilities, and optional digital interfaces (including a new USB port) complete the picture.

information

Envoice MkII, 758.69 Euros (around £512); DI-Mod USB, 434.55 Euros (around £293). Prices include VAT.

Mindprint +49 6851 905210.

+49 6851 905200.

info@mindprint.com

www.mindprint.com

Published April 2004