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Page 2: Slate Digital Virtual Microphone System

Microphone, Preamp & Modelling Software By Neil Rogers
Published November 2016

AKG C12

Next up was the AKG C12, another legendary valve heavyweight and a beautiful mic to see and use first hand. [It should be noted that the C12 that FX Rentals provided us with had been fitted with a nylon-rimmed capsule, rather than the original brass-ringed type. These do have significant sonic differences, but since for many years AKG themselves fitted C12s with the nylon variant when carrying out repairs, the microphone we used for the test is still arguably an ‘authentic’ C12 — Ed.]

Listening to our female vocalist Grace first this time, there seemed much more of a difference to me with this model, in that the VMS felt slightly ‘wispy’-sounding, lacking in body and prone to some slight sibilance issues. The real mic, however, sounded balanced and bright, without any harshness, and a couple of members of the SOS team were raving about the ‘smooth’ top end.

On Sam’s vocal, the VMS did a much better job, and, whilst not sounding exactly the same, I would quite happily have used either. The VMS seemed brighter than our C12, which seemed to suit Sam’s voice more in this context.

With our voiceover sample, there wasn’t a huge amount of difference, with the VMS doing a good job of presenting Jules’ voice, with perhaps just a whisper more sibilance than on the real thing.

Neumann U67

Turning next to the Neumann U67, it’s worth starting off by saying just how much we all liked the sound of the original that FX Rentals had lent us. The main word I can think of to describe the sound is ‘balanced’. The way this mic softens the top end of a source is a lovely, lovely thing, and you could dial in plenty of high-frequency EQ before things started getting harsh. Could the VMS get us there at a fraction of the price? Well, although it provided very useable results, I felt that on this particular microphone the differences were greater than with all the others. On Grace, in particular, the VMS 67 sounded more ‘tizzy’ and sibilant, while on Sam the real mic sounded smoother and more ‘whole’ in the mid-range area. It’s important to note, though, that we were actively looking for these differences, as we were comparing it directly to a seriously good-sounding — and seriously expensive — vintage microphone. [After the review, we discovered that Slate's U67 emulation is actually derived from a modified version of the mic with the 'broadcast filters' removed — a common modification which results in a more open and extended top-end. This would account for the tonal variances we observed in comparison to our 'stock' hired mic — Ed]

Sony C800g

The last microphone we auditioned was one that I’d never had the pleasure of using before. The Sony C800g is certainly a distinctive-looking beast, with its large fin-like heat-sink protruding from the mic body. Taking in the sound of the real microphone first, we all liked its ability to push the top end of a vocal without getting harsh. It surprised us especially with its ability to offer a different perspective on a performance, and Mike Senior, in particular, was very taken with how it was able to seemingly change the feel of a song.

Superlatives abound, then, but how did the VMS compare? On our voiceover artist, Jules, it did a pretty good job: there was a difference in the lower-mid region, but with the intensity increased in the software, the difference was reduced. The brightness and general characteristic were close though. On Sam’s vocal, we felt that the VMS was doing a pretty decent job of capturing the feel of the mic, although that top-end boost almost felt a bit ‘forced’ at times. For what it’s worth, there was a noticeable difference in the sound of the guitar spill on this recording — again, not good or bad, just different. For Grace’s voice, however, the VMS was a little wide of the mark for me. As with the C12 model, the VMS seemed a little hollow-sounding, and that distinctive top end was just not the same, with a small but clear increase in sibilance issues and general harshness. [Again, after the review we discovered that Slate offers two VMS models for this mic as its sound character apparently changed during its production. For the original review we used the standard model, but the alternative 800M version has a slightly darker character which much more closely matches the hired C-800G we were using. An additional audio example file using this second model has been added to audio resources — Ed]

Female vocalist Grace Kuhl compares the Sony C800g to the Slate emulation.Female vocalist Grace Kuhl compares the Sony C800g to the Slate emulation.

General Observations

Judging two sounds that are similar can be a highly subjective thing, of course, and it would certainly be interesting to compare some of the models in more of a ‘blind’ setting. Human nature being what it is, it’s also true that if we look hard enough for a problem, we can usually find one. We also all have different things we look for in a microphone, with my ears seemingly being particularly sensitive around the sibilant 4-7 kHz region. It’s also worth making the point that in all the recordings we did, the VMS gave results that, at the very least, we felt we could work with.

For me, the U47 was the most accurately modelled, and I felt it did a great job on all of the performances, but the C12 was also very well represented. Across all the models, it was only on Grace’s female voice that I felt the VMS was often a little off the mark — especially on the Neumann U67 and Sony C800g. The intensity control on the VMS software was useful, though, and there was more than one occasion when this enabled a nice amount of control over the emulations’ ‘body’ or ‘fullness’.

We were concerned about the system’s ability to model a mic’s off-axis response, but whilst there were certainly differences in both tone and level with all the mics, it didn’t necessarily seem like it would cause any problems in a mix. Listening closely on headphones, there was also a small difference in the amount of recorded room sound on some of the models, which again points to differences in the off-axis response.

Virtual Reality?

If you’re a microphone enthusiast like me, then I’m sure you’ll appreciate what a pleasure it is to get your hands on some of these classic microphones. Everything about them, from the large external power supplies and quirky cabling, to having to let the tubes warm up, gives a sense of gravitas to a session. Part of this, of course, is the visual impact they have in a live room and, with the older mics in particular, there is a reassuring sense of heritage combined with a curiosity with what that paticular mic might have seen and heard during its lifetime. It feels good, even inspiring, and so long as they’re well serviced and fully operational, they sound fantastic. If the VMS allows a whole new group of engineers to get close to the sound of these vintage classics, however, then many artists — and the listener, of course — won’t care how nice it was for those involved during the recording session! You do, of course, also have to consider the ever-rising cost of these classic mics. At least a couple of the models we tested have gone way beyond the realms of being practically obtainable unless you have plenty of disposable income, or are looking at an investment or collector’s item.

So does the Slate VMS system break down some walls for analogue modelling? For a couple of the examples from our recording session I felt that the differences were reasonably significant, with the VMS versions of the Neumann U67 and the Sony C800g being the ones that I felt were a little lacking. There also seemed to be an inherent ‘modern’ characteristic that remained from the source microphone; whilst certainly not unpleasant, this resulted in a brighter sound that could become sibilant. In the vast majority of our examples, however, the VMS did offer a very believable flavour of the mic in question and, more importantly, I felt I could always happily work with what it was capturing. The fact that six engineers sat debating some of the nuances of the various models after the session was a testament to just how close these comparisons became!

Stepping back for a moment, though, I’ve always felt that whilst it is a real treat to use some of the classic mics, the increase in perceived ‘quality’ is a textbook example of diminishing returns. Once you get past a certain level of microphone, the differences become much more subtle and subjective. In my own engineering work, for example, whilst I can hear, and certainly appreciate, the subtle difference between my own old Neumann U87 and a borrowed U67, I’ve never once felt like it was holding back a particular recording. However, even the U87 is pretty expensive in its own right now, so the biggest question should perhaps be how the Slate VMS compares against microphones occupying a similar price point. If you’re looking to make your first serious mic purchase, or to start expanding your mic options, then it could be a very tempting proposition. Indeed, Mike Senior made a compelling argument when we were discussing this issue, pointing out that for a voiceover studio or small vocal production setup, the VMS could remove the need to have multiple mics for different voices, and would therefore represent excellent value for money.

The VMS sounds good in its own right. So what is of real interest with this new technology is not so much how accurate it is in modelling a particular microphone, but rather how it might change how we work. Whilst it can be a drag auditioning microphones sometimes, it is a big part of the craft of studio engineering. Do you really want to have the ability to change the microphone during the mixing stage? We have so much choice now with mixing software that maybe one more option might not make that much difference, and it could even become a much more creative part of the process. It could also make our lives easier regarding accurately matching a mic to a voice, meaning the need for less consequent mix processing.

Conclusions

I suspect for many engineers, particularly those who own some nice microphones already, a ‘virtual microphone’ will be perceived as a step too far. Looking at the package as a whole, though, you are getting a good-sounding large-diaphragm capacitor microphone and preamp for your money as well as the software, and Slate Digital have obviously been careful to make sure the capsule and associated electronics are of a certain standard, or the system just wouldn’t come close to working.

I would describe the preamp component of the system as functional, while the all-important modelling software really is quite good. It’s not always indistinguishable from the real thing, but at times it gets you frighteningly close, and in the context of a mix, or on less than stellar monitoring, you’d be hard pushed to tell the difference. In my own studio, I can imagine using the VMS in a complementary fashion, alongside my other microphones, and it could open up some creative post-production options with backing vocals and the like. For some projects, you could perhaps also use the VMS as a mic-matching tool at the pre-production or demo stage, with a view to possibly hiring the real thing for a few days of key vocal tracking.

These are interesting times we live in, and the VMS certainly sounds good enough that I’d be very surprised if there wasn’t more to come from this type of technology over the next few years. Whether this idea is exciting or horrific to you — delete as appropriate — it’s going to be fascinating to see how things develop, and whether serious numbers of people embrace this new way of recording and mixing.

All the audio files from our session are available on the SOS web site, so why not have a listen for yourself and see if you can hear the difference?

Watch the SOS video all about the review session and methodology at: www.soundonsound.com/reviews/slate-digital-vms-classic-mic-shoot-out

The AKG C12

The AKG C12.The AKG C12.One of the most highly regarded microphones from Austrian manufacturers AKG is the original C12, introduced in 1953 and remaining in production for a decade until 1963. Its CK12 edge-terminated twin-diaphragm capsule is often claimed to be the finest capacitor microphone capsule ever designed, and it actually operates in a fundamentally different way to the Neumann M7-based design (the AKG system relying on a resonator design while Neumann capsules employ an ‘aperiodic’ concept). In fact, the CK12 capsule evolved quite a lot over the years, with different diaphragm materials (styroflex or mylar) and thicknesses (10, 9 or 6 microns), and changing dimensions of the back-plate chamber (in an effort to increase sensitivity, but with the side-effect of an increased HF response which became a key characteristic of the C12 sound).

The microphone itself was also constructed with different output transformers over the years, too, although it always employed a 6072 double-triode valve as the impedance converter. Consequently, there are probably more variations of AKG C12 than any other vintage production microphone.

Nevertheless, the CK12 capsule went on to form the basis of the classic C414 microphone and it has inspired the design of many of AKG’s large-diaphragm capacitor capsules ever since. An original C12 microphone in good condition today can cost around £12,000.

One of the unique aspects of the C12 at the time was its provision of nine switchable polar pattern options rather than just two or three! However, the pattern couldn’t be selected from the microphone itself; instead, the mic was connected to a bespoke power unit (called an N12), and another multicore cable ran out to a dedicated remote control box called the S12 which also provided the audio output connection. A huge rotary switch on the S12 box selected the desired polar pattern, allowing decisions to be made and auditioned from the control room for the first time.

AKG released a re-issue version of the C12 in 1994, called the C12VR. However, while this also employs a 6072 valve for the impedance converter, both the capsule construction and electronic circuitry are significantly different, and so too, therefore, is the sound character.

Bizarrely, there is a tenuous connection between the AKG C12 and the Neumann U47. In the late 1950s Neumann managed the worldwide distribution of their own microphones, leaving Telefunken without the hugely successful U47 as their flagship studio capacitor mic. Consequently, Telefunken commissioned AKG to produce a bespoke version of the C12, but with a simplified polar pattern selector on the microphone itself.

The result was the Telefunken ELA M 250E, with cardioid and omni pattern options, and it was built into a slightly fatter body than the original C12 to accommodate the extra switching and circuitry. Inevitably, the new simplified circuitry, different internal construction, and different head grille shape and size contributed to a noticeably different sound character compared to an original C12, but it was a superb mic in its own right and a subsequent variant called the ELA M 251E, with a third figure-of-eight polar pattern option, became hugely popular and very well known in America. Siemens marketed OEM versions of the ELA M 250 and 251, called the SM203 and SM204, in Europe. Hugh Robjohns

The Neumann U67

The Neumann U67.The Neumann U67.When warned of the impending obsolescence of the Telefunken VF14 valve, Neumann set about developing a new microphone to replace the U47 and, starting from a clean sheet of paper, the company’s engineers took the opportunity to introduce several significant engineering improvements. The most obvious evolution was to the microphone’s shape, introducing the iconic conical body and chisel-head grille to appeal to a far more style-conscious 1960s market.

One of the most important changes was to redesign the way the capsule was constructed, building it as two separate, self-contained halves which could then be bolted back-to-back. This form of assembly was not only much simpler, but crucially it made it far easier to match precisely the diaphragm tensions across a batch of capsules. The resulting twin-diaphragm, centre-terminated capsule was christened the K870/67, using polyester foil diaphragms sputtered in gold. Apparently, this innovative design has become the most copied capsule in the world today!

The impedance conversion circuitry was also substantially more advanced than that of the U47. Based around a Telefunken EF86 pentode, wired again as a triode, a tertiary winding on the output transformer provided negative feedback to improve distortion, and a steep roll-off below 30Hz was implemented in the grid circuit to help prevent low-frequency overloads due to wind, pops, vibration, and so on.

Also, instead of needing separate mics to obtain different polar patterns, the Neumann engineers built in the ability to select cardioid, omni, or fig-8 polar patterns via a switch just below the grille. Two more switches enabled a 10dB pad and a high-pass filter — options made necessary by the growing popularity of close-miking techniques, to prevent overloads and control the proximity effect.

Since this all-new microphone was designed and introduced in 1960, the first production batch was launched as the U60. However, Neumann’s US distributors at this time, Gotham, persuaded Neumann to change the model name to the U67 to capitalise on the great success and popularity of its predecessor, the U47. The U67 microphone remained in production from 1960 through to 1971, and there was a limited-edition reissue in 1993. Original U67 mics in top condition can change hands today for as much as £12,000.

A solid-state replacement for the U67 was introduced in 1967 but, as the ‘67’ model name was already taken, this new microphone was christened the U87 and has become arguably the best known of all Neumann mics. In fact, the U87 was amongst the first phantom-powered microphones introduced by Neumann, but the relatively low operating voltage this provided required a slightly different capsule construction, known as the K87

However, a sister microphone, introduced the following year and called the U77, operated on a 12V AB-power system and so needed a DC-DC converter to generate a sufficiently high capsule-biasing voltage, allowing use of the U67’s original K870/67 capsule. When the U87 was re-engineered in 1986, the internal battery section of the original design was removed and a DC-DC converter incorporated, allowing the U87 Ai model to revert to using the K870/67 capsule as well. Hugh Robjohns

The Neumann U47

The Neumann U47.The Neumann U47.The U47 was the first capacitor microphone to be launched by Neumann following the company’s relocation to Berlin after the Second World War in 1947. As with many other Neumann microphones, its model number derives from the year of its conception, although it wasn’t officially launched until 1949. Today, good-condition U47s can change hands for in excess of £10,000.

As the world’s first commercially-available, switchable-pattern capacitor mic, the U47 was a ground-breaking product. Although it originally used the same M7 capsule that was developed for Neumann’s pre-war CMV3 microphone — a twin-diaphragm, centre-terminated design with PVC diaphragms — it used the capsule in a revolutionary new way. Whereas the rear diaphragm was left disconnected in the CMV3, bestowing a fixed cardioid polar pattern, a switch just below the grille of the U47 allowed the rear diaphragm to be polarised as well, enabling the user to switch between a cardioid or omnidirectional polar pattern.

From 1956 the capsule was redesigned to use more stable polyester diaphragms and was consequently re-named the K47/49, but it was still fundamentally very similar to the original M7 capsule. Specifically, it was a one-piece design with a shared middle electrode — an approach which made it difficult to match the tension of the front and back diaphragms, and thus made the omni pattern rather variable between production models. A sister microphone called the U48 was launched in the mid 1950s, offering the user a different choice of polar patterns switching between cardioid or figure-of-eight, the latter achieved by subtracting the output of the rear diaphragm from that of the front.

The microphone’s impedance converter was built around a Telefunken VF14 pentode valve operated as a triode, but by the late 1950s Neumann were the only remaining customers for this particular design and so Telefunken ceased its production. Naturally, Neumann searched for a suitable replacement valve and released the U47N model in 1962, with a Nuvistor valve, but the sound character was not the same and the U47 was finally withdrawn in 1965 — officially replaced by the U67 model.

Throughout the 1950s the worldwide distribution of Neumann mics was handled by Telefunken. The company were also allowed to rebrand the mic in the USA as the ‘Tele 47’, and it was in this form that the U47 quickly usurped RCA’s ribbon microphones as the studio standard. This is why one of the best-known vocal artists of the period, Frank Sinatra, often referred to singing into his ‘Telly’ mic — meaning the rebadged Neumann U47.

A solid-state version of the U47, using exactly the same K47/49 capsule, was introduced in 1969, called the U47 FET, but while it had many excellent qualities and has gone on to become an iconic microphone in its own right, it had a different sound character to the original valve U47. Hugh Robjohns

The Sony C800g

The Sony C800g.The Sony C800g.The extremely distinctive Sony C800g valve capacitor mic was introduced 1992 and is still in production today, costing around £7600. The design aim was to create ‘the definitive vocal mic’ with the highest possible sound quality, and it does have something of a unique sonic character which is extremely open and airy, without sounding harsh or emphasising sibilance. The polar pattern can be selected between omni and cardioid via a switch on the mic body.

The impedance conversion circuitry is built around a 6AU6A pentode valve, and the C800g is unique in featuring a built-in thermoelectric cooling system, which accounts for the large rearward projection and heatsink! Based on the Peltier principle, this cooling system has no moving parts or liquid. Instead, a semiconductor material is sandwiched between two metal plates and, when a DC voltage is applied across the material, a temperature differential builds up between the two metal plates. One plate is connected to the external heatsink and remains at ambient room temperature, forcing the other plate to get cooler, helping to reduce the thermal noise of the electronic circuitry. A two-part aluminium body is designed to minimise mechanical noise conduction to the capsule. Hugh Robjohns

Hear For Yourself: Audio Files

All the audio files captured in this session have been made available in a Zip file on the SOS web site, so you can compare the original microphones with the VMS models. To download the files, click the link.

Download | 140 MB  Download Update | 75 MB

Steven Slate Responds

As pointed out in the review, the rented microphones that we used for our review of the VMS weren’t the very same well-kept examples that Slate Digital used for their modelling purposes. In fact, one of the selling points of the VMS is that the microphones upon which the models were made are some of the best examples that Slate could source.

It should be no surprise, then, that there are some audible differences between the classic mic audio and the VMS modelled audio. After all, no two vintage microphones necessarily sound exactly the same anyway.

To demonstrate the capabilities of the VMS algorithms, though, Slate Digital founder Steven Slate has taken the time to create a range of new audio files using the VMS developer tools to better model our rental microphones.

Slate explains: “To get a model of the microphones I analyzed two sources against the flat VMS files. The two sources are the Grace and Jules files. To model mics with VMS, we usually use about 40-50 sources ranging from voices to noise tests (such as sine and square waves), and we do measurements at many different distances, in different spaces, and at different angles. Then we run special tests with our own tools to measure the exact nonlinear responses from the tube circuits of the mics.  Each tube circuit is extremely unique and crucial to the overall depth and tone of the microphone’s sound.

So given that we had very little data to analyze, I first had to put in place the current tube algorithms that we already had for the VMS stock models. Then I separated the vocal parts into different amplitudes so they could be analyzed independently. Then our software is able to produce a general model. For these voices, I felt our analysis software combined with the stock models got us about 85% there.

So then, I hand tweaked by ear the VMS tools which can control dozens of details from harmonics, transient response, low end resonances, and more. After about twenty minutes of tweaking each mic, I now think it’s about 97% close to the rented vintage mics.  In a mix, I do not think that people  will hear a difference in a blind test. I also think any discrepancies with the brightness and sibilance has completely vanished. I’d hope that the files could be listened to blindly, several times, to see if the vintage mic in each pair could consistently be identified.”

We invite you to do just that. Slate’s new audio is available above in the slate-vms-1116-update.zip file in the ‘Media’ section in the article sidebar.

Special FX

We’d like to thank the excellent pro-audio hire company FX Rentals for the use of their classic microphones, without which we wouldn’t have been able to perform this unique experiment.

www.fxgroup.net

Watch The Video

Watch the SOS video all about the review session and methodology.

Pros

  • Creates believable emulations of some of the classic tube microphone models.
  • Relatively affordable package.
  • The included microphone sounds good on its own.
  • Good-quality case and shockmount.
  • Ability to change the microphone model after the recording session.

Cons

  • Ability to change the microphone model after the recording session!
  • System is dependent on a decent, low-latency recording setup to work in real time.
  • Some minor sibilance issues on some singers.

Summary

The VMS is a bold new product that can deliver on its promise to recreate the sound of some of the classic microphone models — at a fraction of the price. Whilst not always being completely indistinguishable, the results were always to a good and usable standard. Perhaps of more interest, though, is its potential to change the traditional workflow of the recording process, in ways which could be both good and bad!

information

£999 including VAT.

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