You are here

Townsend Labs Sphere L22

Microphone Modelling System
Published November 2017
By Sam Inglis

Townsend Labs Sphere L22

Townsend Labs’ Sphere L22 boldly goes where no mic emulation system has gone before!

Studio owners have spent the last decade being bombarded with digital emulations of classic hardware. Everything from analogue synthesizers to preamps, compressors and equalisers has been transmuted into a software plug-in, and now it’s the turn of the humble microphone. However, different manufacturers have different ideas about what a ‘modelling’ or ‘virtual’ microphone should do.

Some have focussed exclusively on capturing the frequency response and non-linear characteristics of classic microphones, basically by applying equalisation and saturation to the output of one microphone to make it sound more like another. This is the basis of both Antares’ Mic Modeler plug-in and of the Slate Digital Virtual Microphone System, and inasmuch as it works, it can only do so within certain parameters. For sound arriving on-axis in a typical close-miking scenario, the VMS in particular can be convincing; but it can’t capture differences between other microphones’ polar patterns, or the character of their off-axis pickup, or the way in which proximity effect behaves in a specific mic.

At the other end of the spectrum, you could also view the SoundField (and other A- or B-format mics), as well as more elaborate systems like the Trinnov SRP, as ‘virtual mics’. The aim of these systems is not to mimic the prized sound of some galactically expensive vintage vocal mic, but to allow microphone orientation, pickup pattern and so on to be modified without moving the mic itself. In other words, it’s not the tone of the microphone that is virtualised, but its polar pattern and directional qualities.

The Sphere L22 from Townsend Labs is an interesting hybrid between these two concepts of mic ‘modelling’. Like the Slate VMS, it is a bundle consisting of a microphone and a plug-in. However, whereas the mic supplied with the VMS has a single, cardioid-only large-diaphragm capsule, the Sphere mic contains back-to-back cardioid capsules with separate outputs. And although this arrangement doesn’t permit the virtualisation of direction that is achieved by the tetrahedral four-capsule array in the SoundField mic, it enables the accompanying Sphere plug-in to do much more than merely recreate the on-axis frequency response of other microphones.

Holy Orders

There are two forms of fundamental or ‘first-order’ microphone. One senses air pressure, and is inherently omnidirectional; the other senses air velocity or ‘pressure gradient’, and has a native figure-8 polar pattern. Other polar patterns are, at least in theoretical terms, achieved by combining pressure and pressure-gradient measurements in different amounts. Combining them equally gives the pattern we call ‘cardioid’ (because it looks heart-shaped when plotted on a graph, though the Germans view it as being kidney-shaped!).

In practice, however, large-diaphragm capacitor microphones do not achieve their cardioid response by combining independent omni and figure-8 capsules. Instead, the sealed chamber behind the diaphragm in an omni capsule is substituted for an acoustic labyrinth that is partially open to the outside world, usually with a second diaphragm behind it. Sound from the rear and sides of the mic enters this labyrinth and eventually makes its way to the rear of the front diaphragm, delayed by just enough to cancel the same sound arriving from the front of the mic — at least over most of the wanted frequency range.

This design succeeds in making the mic less sensitive to sound arriving off-axis, but the polar pattern that results is cardioid only within a limited frequency range, typically around 1kHz or so. Further up the frequency spectrum, large-diaphragm ‘cardioid’ mics become more hypercardioid or supercardioid, while at the bass end, they are to all intents and purposes omnidirectional (although the precise behaviour also varies with source distance). Furthermore, these variations are typically quite uneven, so sound arriving off-axis is not only attenuated but subjected to complex filtering that usually makes it sound quite bad. They also vary considerably between different mics, so they could be considered part of what gives a particular mic its own character.

The Sphere plug-in is available in VST (2 and 3), AAX and AU formats, as well as for the UAD2 platform.The Sphere plug-in is available in VST (2 and 3), AAX and AU formats, as well as for the UAD2 platform.Many large-diaphragm mics have switchable polar patterns. These usually include cardioid, omni and figure-8, and sometimes additional patterns such as hypercardioid, and this flexibility is achieved by using both diaphragms rather than just the front one. Adding their contributions together in equal amounts gives an omnidirectional pickup, while reversing the polarity of one creates a figure-8 microphone. Unsurprisingly, however, this approach to synthesizing first-order polar patterns yields only a fairly rough approximation of the ideal! Additionally, there is often substantial variation in the on-axis frequency response between the different pattern settings.

Mr Beam

The key innovations of the Sphere system are enabled by the use of very closely matched cardioid capsules, with known characteristics. By comparing their outputs, the Sphere plug-in is able to resolve the combined signal into those theoretical omni and figure-8 components. This in itself is not new — the SoundField mic achieves its magic by synthesizing an omni component and three orthogonal figure-8 components — but, using patented ‘beam-forming’ techniques, the Sphere certainly does some new things with the information.

Foremost among these is the ability not only to mimic both the on- and the off-axis characteristics of other microphones, but to separate these two elements from one another. So if what you’re after is a faithful recreation of classic mics like the Neumann U47 or an AKG C12, the Sphere L22 will deliver. This includes modelling the non-linear characteristics of the microphone’s electronics, but unlike previous modelling microphones, the Sphere system will replicate much more than just their on-axis frequency response in cardioid mode. it also allows you to operate those mics in their other polar patterns, and generates not merely a generic omni or figure-8 pattern, but one which reproduces the complex, frequency-dependent variations of the originals. The Sphere’s recreation of, say, a U47 is thus said to be faithful not just in terms of sources directly in front of it, but also in terms of polar pattern, off-axis pickup and proximity effect.

The Sphere system isn’t limited to faithfully recreating classic mics, however. It also extends their capabilities — and, daringly, seeks to correct their flaws. So, regardless of how many polar patterns the original mic has, the Sphere model offers nine, spanning the full range from omni to figure-8 with cardioid at the mid-point. And whereas proximity effect is usually an inevitable consequence of the choice of polar pattern, the Sphere L22 breaks that link, allowing you to freely vary the amount of proximity effect in any directional pattern. Perhaps the most radical and interesting innovation, though, is something Townsend Labs call Off Axis Correction.

Engaging Dual mode allows you to blend the signal from two different modelled microphones, and also reveals the controls for Off Axis Correction, lower left.Engaging Dual mode allows you to blend the signal from two different modelled microphones, and also reveals the controls for Off Axis Correction, lower left.The idea behind Off Axis Correction is, in a nutshell, to let the user change a mic’s polar pattern and improve its off-axis response without affecting the tone of its on-axis pickup. So if, like me, you prefer the vocal sound of a U87 in cardioid, but you want the best possible rejection of an acoustic guitar being played by the singer, Off Axis Correction will let you put the virtual mic into figure-8 whilst retaining the cardioid mode’s on-axis sound. What’s more, the off-axis frequency response and proximity effect can be manipulated independently of the on-axis pickup, to make any spill that is captured sound more natural. All this is explained in more detail in a White Paper on Townsend Labs’ web site, and in a fiercely technical patent document.

Out Of The Box

The Sphere microphone comes in a smart black attaché case, which also holds all the necessary accessories. These include a cat’s-cradle shockmount and swivel mount, and a Y-shaped cable with a five-pin XLR at the mic end and two conventional three-pin XLRs at the other end. The mic itself is surprisingly large, and although it can’t match the sex appeal of a vintage classic, it looks smart enough until you plug it in, whereupon four bright white LEDs light up the entire headbasket. I suppose there’s an argument that this makes it easier to position the capsule very precisely, but if I owned the mic I’d be tempted to disable them; this can be done by moving an internal jumper, without invalidating the warranty.

The mic’s dual, centre-terminated capsules need separate preamp channels, both with phantom power. Unlike Slate, Townsend Labs have chosen not to supply a preamp with their modelling mic. They say that any standard preamp will be fine, but caution that it’s vital to ensure precise gain matching between the capsules. If you don’t have a preamp with stepped or digital gain controls, the mic has a calibration mode, engaged by a small switch on the rear, which makes it easy either to dial in the right amount of gain on a continuously variable control, or apply an offset within the plug-in to compensate for gain mismatches. A second switch introduces either a 10dB or a 20dB internal pad for coping with loud sources.

With an equivalent noise level of 7dBA and a maximum quoted SPL of 140dB for 0.5 percent distortion, the mic itself comfortably outperforms the vintage models it emulates, at least from a purely technical point of view. Sensitivity is specified as 22mV/Pa, which makes the mic a little less hot than the current U87Ai in cardioid mode, and should be eminently manageable in any recording context.

The dual outputs of the mic need to be recorded to a stereo track in your DAW, on which you then insert one of two plug-ins, called Sphere and Sphere 180. The latter is employed where you want to use the Sphere as a stereo mic (see box), though this capability is perhaps best seen as a fringe benefit rather than a core feature of the design. Both plug-ins are available in all the usual native formats, so should work with any DAW as long as it supports stereo-in/mono-out plug-ins, and also for Universal Audio’s UAD2 DSP processors. This means that if you own a UA Apollo, you can monitor through the Sphere plug-ins with minimal latency. And, of course, you do want to monitor through the plug-in if at all possible; where it isn’t possible, you might be better off just having the left (front) input in the monitor mix.

Poles Apart

Thankfully, all of the sophisticated processing is kept well behind the scenes in the Sphere plug-in. In its basic format, this is refreshingly straightforward: clicking on the big picture of the selected microphone cycles through the different mic models, while a nine-position rotary dial selects the polar pattern. Patterns that were available on the original microphone are illuminated in blue, but there’s nothing to stop you selecting the others. Where the original microphone was also a large-diaphragm capacitor mic, these ‘missing’ patterns should correspond pretty closely to what you’d get if they were implemented in real life; but where a ribbon or moving-coil mic is modelled, they naturally represent a flight of the imagination on Townsend Labs’ part.

Next up is a dial called Filter. This has three active positions, all of which are available for all mic models; again, some are highlighted in green to indicate that they model the specific behaviour of the original. As the name suggests, most of these introduce different high-pass filters, but in cases where the original mic has a switchable pad that affects its sound, this will be one of the options.

Townsend Labs Sphere L22The third of the four main controls visible in the basic Sphere interface is labelled Axis, and is continuously variable from 0 to 180 degrees. Rotating this control simulates the effect of moving an on-axis source progressively further off-axis (the reverse is not possible!), which might be useful if, for instance, you find you need to tone down the top end on a backing vocal at mixdown, or want to mellow out a recorded guitar sound a little. Lastly, the Proximity dial allows you to vary the amount of proximity effect that is contributed by the figure-8 component of the sound. Its effect thus increases from none at all, in omni mode, to fairly radical tone-shaping in figure-8 patterns. It should be pointed out that this is not a simple equaliser: although it has some effect at all distances, it’s much more pronounced on closer sources. Completing the main control set are an output gain control, a polarity switch and a button labelled Rev, which reverses the orientation of the virtual mic so that the back becomes the front and vice versa.

You also get visual feedback, courtesy of something Townsend Labs call the Polar Meter. This shows, in blue, the actual polar pattern of the mic being modelled, in whatever pattern setting you’ve chosen. It’s interesting to see how much the nominally ‘cardioid’ pattern varies between different models; the Telefunken ELAM 251 is distinctly subcardioid, while the Neumann U47 is closer to supercardioid. Townsend Labs are surely correct in claiming that this is a part of what gives such mics their special character. Superimposed on the blue polar pattern graph is an animated display in yellow, which shows the angle of incidence of the sound that’s being picked up by the microphone. Since the Sphere can’t differentiate between left and right (or up and down), this pattern is always symmetrical. The idea is that by identifying the angles from which unwanted spill is arriving, you can choose the polar pattern that best serves to reject it. In use, it’s effective and often surprisingly informative, but it’s a shame that the Polar Meter can only display what’s going on at 1kHz — it would be nice to be able to visualise how the polar pattern changes with frequency.

Dual Rectification

Clicking an innocuous-looking button labelled Dual makes visible a large array of additional controls, including the aforementioned Off Axis Correction parameters. However, the feature that gives this button its name is the ability to use two separate mic models at the same time. You can blend between the two in any degree you like, and a Link button gives you the option to tie together their pattern and filter settings. Oddly, linking also applies to the choice of virtual mic, which is not so helpful; another limitation is that since the Sphere plug-in is available only in stereo-to-mono format, you can’t independently pan the outputs of the two mics within your DAW.

The Dual mode makes sense of Townsend Labs’ decision to include models of the humble SM57 and C451 alongside the classic valve mics. These are commonly paired with other mics when recording electric guitars and the like, so Dual mode allows you to simulate a phase-matched combination of, say, a U67 and SM57 in front of a guitar cab. And they don’t have to be phase-matched: a control labelled Align lets you virtually slide the second mic by up to 2cm in front of or behind the first, for those occasions where you want to sculpt a guitar sound though cunning virtual mic positioning. Another parameter that appears only in Dual mode is Proximity EQ. This applies low-frequency boost or attenuation that has the same sort of character as proximity effect, but is independent of the polar pattern and hence audible in omni patterns as well as directional ones.

Off Axis Of Evil?

And so to Townsend Labs’ trademarked Off Axis Correction, which has its own corner of the plug-in interface in Dual mode. It’s quite hard to get a grip on what exactly this does, and although the documentation is generally very good, I feel Townsend Labs have struggled to explain this particular feature as clearly as they might have. Perhaps the best way to think of it is as follows. When Off Axis Correction is disabled, the pattern control mimics as closely as possible the behaviour of any pattern control on the mic being modelled. This means, first, that the actual pattern can vary widely from the ‘ideal’ cardioid, figure-8 or whatever, and secondly, that the tone of the on-axis pickup is altered when you change the pattern setting.

With Off Axis Correction enabled, the main pattern control still introduces the same tonal changes, but has no effect on the actual polar pattern. Pattern selection is now delegated to a second control, which operates independently of the first. The same nine pattern symbols appear round the edge, but the control itself is continuously variable rather than stepped, and instead of a realistic emulation of the flawed off-axis pickup of the real mic, what you get is as close to the theoretical ideal as possible. The on-axis tonal characteristics of the modelled mic are then applied to this ‘improved’ off-axis response. In other words, the aim of Off Axis Correction is not to perfectly mimic the behaviour of the original mic, but to apply its distinctive sound to an idealised three-dimensional pickup.

This leaves open the question of exactly what off-axis characteristics should count as ideal. In some circumstances, the ‘ideal’ characteristic would be the one with the deepest off-axis nulls, but in other situations, the ideal might be minimum coloration of sound that arrives off-axis, rather than maximum attenuation. With this in mind, the Sphere plug-in lets you choose from four settings labelled Free Field, Diffuse Field 1, Diffuse Field 2 and Auto. The Free Field response maximises off-axis rejection, while the Diffuse Field 2 setting focusses on making the off-axis pickup as neutral as possible. You’ll get more spill in the latter mode, but that spill will sound natural. Diffuse Field 1 is somewhere between the two, and Auto automatically corrects the low-frequency response to compensate for moving sound sources, or in situations where multiple sound sources from different distances are being picked up.

Townsend Labs Sphere L22In the first three modes, this low-frequency correction is applied manually using two controls labelled On Dist and Off Dist. The idea is that you can tell the Sphere plug-in how far away the source you’re miking is, and also the distance of whatever is the biggest source of off-axis pickup. It then adjusts both the on-axis capture and the idealised off-axis pickup to give a linear low-end response at those respective distances.

So Much For The Theory

There’s a lot of heavy lifting going on behind the scenes, then, but thankfully, this is pretty much invisible to the user. Apart from the need to match the preamp gain across two channels, using the Sphere as a substitute for a vintage mic is really no different from using the Slate VMS in exactly the same role. You simply insert the plug-in on the track, pick your microphone, and away you go. UA Apollo users also have the added benefit that the UAD version of the plug-in can be employed within the UA Console utility with minimal latency. And one feature that’s easy to overlook, but essential in making the Sphere system work properly, is that the level matching seems extremely consistent throughout: not only when you switch between mic models, but also when you change polar pattens and other settings.

How authentically does it recreate the sound of vintage mics? Alas, I don’t have a U47 or C12, but I was able to conduct pretty extensive comparisons with an original Neumann U87, and also with an AKG C451 with CK1 cardioid capsule. In both cases the Sphere was impressively close, to the point where any differences I heard between the real and the modelled microphones could easily have been down to slight differences between takes, or between their respective positions when compared on a single take. The characteristic on-axis tonal change that occurs when you switch a U87 into figure-8 was reproduced with uncanny authenticity, as was the peaky tone of that mic’s off-axis coloration on sources recorded behind or to the sides of the mic.

Whether or not the Sphere’s models of classic valve mics are equally accurate, they certainly sound good, and have the broad tonal qualities you’d expect. And although there are audible differences between them, they are often quite nuanced and delicate: Townsend Labs haven’t created exaggerated, cartoon-like caricatures of the classics, and nor does the Sphere system allow you to emulate preamp saturation or crank up the ‘valviness’ in the way that the Slate VMS does. Personally, this isn’t a feature I really missed, but it perhaps means that it might take longer to recreate certain classic sounds using the Sphere system, as you’d have to pair it with other plug-ins.

These, according to the Sphere plug-in’s Polar Meter, are the actual polar patterns at 1kHz for the Telefunken ELAM 251, Neumann U47 and Sony C800G, all in their cardioid setting. It’s no surprise that they don’t all sound the same!These, according to the Sphere plug-in’s Polar Meter, are the actual polar patterns at 1kHz for the Telefunken ELAM 251, Neumann U47 and Sony C800G, all in their cardioid setting. It’s no surprise that they don’t all sound the same!Where the Sphere leaves existing mic emulations behind is in the way it replicates not just the on-axis frequency response of classic mics, but their polar patterns and off-axis characteristics. Some readers might be wondering whether this is necessarily relevant to typical use cases: after all, many of us only ever record close-miked sources such as vocals and acoustic guitars, and rarely, if ever, allow our mics to venture into the midst of a full band playing live. But there are very few recording situations where off-axis pickup is non-existent. In the case of vocal recording, for instance, not only will the performer’s chest resonances be arriving off-axis, but there is bound to be some pick up of room ambience, even in a vocal booth. With instruments that thrive in a slightly livelier environment, such as acoustic guitar or violin, early reflections and other reverberation may well be a significant part of the sound. It’s not unreasonable to suggest that a part of what makes a U47 sound different from a C12 has to do with the different ways in which this off-axis sound is captured.

The ability to vary the polar pattern after the fact can also be surprisingly useful for adjusting the tone of the on-axis pickup. I particularly enjoyed using the Sphere as a close mic on things like bass amps and kick drums, where varying the polar pattern and proximity effect gives you a very effective and natural way of altering the sound that’s captured.

One Step Beyond

For me, though, the really exciting aspect of the Sphere system is the way it goes beyond emulating other mics. Yes, it’s great to have a virtual U67 that can be swapped out for a virtual ELAM 251 at the click of a mouse button, and it’s even cooler to be able to combine the two. But it’s Off Axis Correction that moves the Sphere into genuinely new territory, and I think it could be considered something of a breakthrough. The problem it addresses is one that has, until now, been an inevitable consequence of the laws of physics, at least as they apply to the design of capacitor microphones! If we wanted the benefits that a large-diaphragm cardioid capsule brings, such as low noise and a forgiving character when worked up close, we have had to put up with the accompanying down sides of inconsistent polar patterns and ugly off-axis coloration.

The improvement that Off Axis Correction makes in this respect is often obvious and immediately noticeable. For instance, when you’re recording a singing guitarist, you can usually achieve the most rejection of voice from the guitar mic, and vice versa, by choosing figure-8 polar patterns. However, with a typical large-diaphragm capacitor mic, this rejection comes at a cost: what off-axis spill is captured generally sounds pretty nasty, and switching the mic to figure-8 in the first place changes its on-axis character. For this reason, I generally prefer to use ribbon mics or small-diaphragm capacitor mics with true figure-8 capsules. Or at least I did, until I heard the Sphere microphone with Off Axis Correction, which really does deliver on the promise of smoothing out the off-axis tone while retaining the on-axis character of your chosen mic. It doesn’t quite bring the Sphere mic into the realms of good small-diaphragm and ribbon mics in terms of off-axis response, but it certainly makes it better behaved than any other large-diaphragm mic I know of, and means there are quite a few situations where you might actually choose the Sphere mic over the ‘real thing’.

Stereo recording with the Sphere microphone is handled by the separate Sphere 180 plug-in.Stereo recording with the Sphere microphone is handled by the separate Sphere 180 plug-in.The Sphere L22 is not a budget item. If you looked around for a while, you could probably pick up a second-hand U87 for the same sort of price, and the conservatively minded might see that as a safer bet. The first U87s are nearly 50 years old, and a good number of them are still in daily use. Both the Sphere and the Slate VMS will only be usable for as long as the relevant plug-in software is available and up to date, and it would be a brave person who would bank on getting five decades’ use out of them. Equally, microphone emulation is clearly a developing field, and there’s always a risk that today’s products will soon be superseded. Considered on its own merits, however, the Sphere L22 is a really impressive system, and if you run a busy studio, you won’t need to use it for 50 years to get your money’s worth from it. In fact, you might well find that it becomes indispensable after a few weeks!

The Models

The v1.1.1 version of the Sphere plug-in that I tested ships with 10 emulations of other mics:

  • LD-47K and LD-49K emulate, respectively, the Neumann U47 and M49. Over the years these mics were in production, both used at least two different capsules, which were designated the M7 and the K47. The ‘K’ suffix indicates that Sphere’s emulations recreate the latter in both cases. The LD-47K offers a thick, rich sound with a very full lower mid-range, whilst the LD-49K is warm, yet more balanced.
  • LD-67 and LD-87 are models of two more related Neumann mics, the U67 and the later U87, which used an almost identical capsule and was intended as a solid-state replacement for its valve-driven predecessor. The overall tonality of the pair is quite similar, but the LD-87 sounds rather harder and more forward in the mid-range.
  • LD-12 and LD-251 model another pair of cousins, the AKG C12 and the Telefunken ELAM 251, both of which used AKG’s celebrated ‘brass ring’ CK12 capsule. Different choices of preamp valve, transformer and head-basket shape meant that the two did not sound identical, and neither do Townsend Labs’ models, but both have an attractive soft mid-range and airy high-frequency lift.
  • LD-800 is a recreation of the Sony C800G valve microphone. With its characteristically bright, in-your-face sound, this is beloved of hip-hop and R&B vocalists everywhere.
  • SD-451 emulates the AKG C451 modular small-diaphragm capacitor mic. More affordable than the Neumann KM84, these sold by the bucketload back in the day, and the aggressively bright character of the CK1 cardioid capsule is thought by many to complement acoustic guitars and the like. Pleasingly, Townsend Labs’ emulation actually recreates four different capsules depending on the selected polar pattern: the CK1, the CK2 omni, CK3 hypercardioid and CK4 (large-diaphragm) figure-8.
  • RB-4038 copies perhaps the most iconic British microphone of all time: the BBC-designed Coles/STC 4038 ribbon microphone.
  • DN-57 is, yes, a recreation of the humble Shure SM57, a microphone which retails at approximately one-16th the price of the Sphere system!

Three additional models are also included. These are Sphere Linear and Sphere Linear Diffuse, which are intended to offer the flattest possible frequency response for sounds in the free field and the diffuse field respectively, and Sphere Direct, which represents the unaltered sound of the microphone.

Townsend Labs told me that they plan to add further models to the core collection as time goes by, and that these will be free additions, though there is also the possibility that special microphone packs will be made available as paid add-ons.

Stereo Sphere

The primary purpose of the Sphere system is to emulate mono microphones, but as the front and rear capsules are recorded independently within your DAW, it can be used as a stereo microphone. The obvious limiting factor is that these two capsules are fixed at a 180-degree mutual angle, which means it’s not possible to recreate any of the most commonly used coincident arrays. However, there are occasions when back-to-back cardioids can be useful: unlike most stereo arrays that use directional mics, this has a 360-degree acceptance angle, which means that it can be used within a group of musicians arranged in a circle. There are also situations where back-to-back microphones are handy in a non-stereo context, for instance when recording dialogue between two speakers, or a vocal duet with the singers facing one another. To use the Sphere mic in stereo, you need to load the separate Sphere 180 plug-in, which is in stereo-to-stereo rather than stereo-to-mono format. Most of the core Sphere features are still available in this plug-in, including Off Axis Correction.

Published November 2017