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Positive Grid BIAS

Guitar Amp Simulator Plug-in For Mac OS & Windows By John Walden
Published January 2015

With component-level adjustment and ‘amp matching’ features, BIAS can target almost any guitar amp sound — real or imagined!

Love ’em or hate ’em, virtual guitar rigs are now a part of the music-technology furniture. For many home, personal or project studios where cranking up an amp is not an option, they are a necessary convenience. However, they also offer a huge range of tonal variations that is difficult to match unless you happen to have a warehouse full of classic guitar hardware. And to many ears (my own included), the quality of the results can be more than good enough to be used in a commercial music-production context.

In the Mac and PC realm there are a number of well-established products: Line 6’s POD Farm, IK Multimedia’s AmpliTube, Waves’ GTR, Peavey’s ReValver and Native Instruments’ Guitar Rig Pro would be among the obvious candidates. However, we now have a new contender in the shape of BIAS from Positive Grid. I say ‘new’ but BIAS is interesting on two counts, the first of which is that it actually started life as an iPad app. Unlike software from the likes of Line 6 or IK Multimedia that has been ported from desktop to iOS, BIAS is coming in the other direction.

Positive Grid BIASSecond, BIAS isn’t quite from the same mould as other virtual guitar rigs. While it does amp, cab and microphone modelling so that you can craft a guitar tone, it also offers an ‘amp design’ function. You can tweak components within the preamp or the power amp, and because it’s all ‘virtual’, it comes without the risk of instant electrocution and sudden death.

Match Making

BIAS is actually available in two flavours. The more affordable BIAS Desktop gives you the amp modelling and amp design features that are the basis of the iOS version. There are 36 default amp models supplied to get you started, and cabinet and microphone modelling are also included. BIAS Professional adds a further element: Amp Match Technology. In principle, this attempts a similar function to the very sophisticated hardware-based Kemper Profiling Amp. In BIAS Professional, the dedicated Amp Match module allows you to sample both your actual sound (the ‘source’) and the sound you would like to recreate in a model (the ‘target’) and then applies a processing algorithm to transform the source into the target.

Cramming all the equipment included within BIAS into your studio is somewhat easier than with the equivalent hardware: a fairly modest 460MB download, a speedy installation and a simple online activation process will have you up and running quickly. With support for VST (32- or 64-bit), 64-bit AAX, AU (32- and 64-bit) or RTAS plug-in formats, just about everyone ought to be catered for.


Whichever version of BIAS you choose, the core features are the amp/cab/microphone modelling and the ability to design your own amp. You can access all of these elements from the main plug-in window, which is split into four horizontal areas. The topmost strip provides access to the preset system and settings menu. Also in this strip is an option called Tone Cloud which lets you download BIAS creations from other users and upload your own models. This works very well, and Tones are also compatible with the iOS version of BIAS.

The next strip contains a visual representation of the signal chain through the various modelling elements, starting with the front panel of the amp and running through to the Amp Match component. The signal chain is fixed, but you can drop either of the two EQ modules and the Amp Match module in and out as required simply by dragging them up or down.

Click on any specific component within the signal chain and it becomes the focus of the next strip. It’s here that you get to tweak the amp model at the component level, whether that’s the visual appearance of the Custom Panel, the valve types used in the preamp and power amp, or the transformer. Finally, the strip along the base of the window provides controls to set the input and output levels, configure the hum reduction, noise gate and room control options and configure and use the ‘quick snap’ panel. The latter allows you to select up to eight presets for easy recall.

Custom Eyes

Each of the modelling components provides you with editable parameters. So, for example, if you select the Custom Panel, not only can you tweak the virtual knobs to adjust the tone as you would on a real amp, but if you click on the small ‘edit’ icon located top-right of the panel, you can then customise various elements of the amp’s appearance. In this module, this feature is mostly cosmetic, but it does allow you to get the visual ‘vibe’ right as a useful reminder of what kind of tone a particular preset is intended to create.

Build your own amp? BIAS allows you to wield your virtual screwdriver and soldering iron in a  safe environment.Build your own amp? BIAS allows you to wield your virtual screwdriver and soldering iron in a safe environment.The rest is far from cosmetic, though. For example, select the preamp and a whole host of components and settings can be adjusted. While you would probably need a PhD in electronics to make any informed choices when configuring the equivalent options in the design of a real (hardware) amp, in BIAS you are free to simply experiment and see where it leads you. Want a more overdriven sound? Then wind up the input tube gain or add an extra tube stage. It’s easy to do, and nothing explodes.

While the preamp and power amp contain perhaps the largest number of tweakable options, there are still choices available within the tone stack and the transformer. Indeed, if you really are serious about crafting your ideal guitar tone, there are endless hours of fun to be had. And if you just want to start gently, each component is also supplied with a set of presets so you can, for example, mix and match from about a dozen Preamp presets, eight Tone Stack presets, and so on.

All of the key amp stages are editable within BIAS.All of the key amp stages are editable within BIAS.Beyond the amp itself, the editing options are perhaps more conventional. There is a series of cabinet models spanning the usual suspects from 1x12 up to 8x10, with plenty of stops in between. Each colours the sound in its own distinctive fashion. You also get a choice of two different microphone models and the option to position these virtual mics in front of the cab. The mic position can influence the tone and volume of the output and, with the room simulation option engaged, you can get some very nice ‘real’ room ambience into your sound.

As with a real amp and most virtual guitar rigs, the more gain you use, the noisier things can become. Having used BIAS alongside both ReValver and Guitar Rig, I don’t think there is much to choose between them on this front, but I certainly found both the Hum Removal and Noise Gate options useful to have once I was into (and beyond) metal territory.

After Effects?

So far, so good. The ‘virtual amp design’ features are very well executed, and the Amp Matching feature of the Professional version is both interesting and, with a little care and effort on behalf of the user, very capable. However, if you are in the market for a single ‘does it all’ virtual guitar rig plug-in, BIAS is currently missing one key component: a collection of virtual stompbox or rack effects. This is exactly as in the iOS version of BIAS but, in that case, Positive Grid have a companion app called JamUp Pro that provides stompbox effects; you can import BIAS amp models into JamUp to create a complete guitar rig signal chain. I’m not sure quite how Positive Grid might address this issue with the Mac and PC versions of BIAS, though they obviously have the signal-processing expertise, as JamUp’s stompbox effects are very good.

BIAS Curious?

Having used BIAS under iOS for quite a while, I wasn’t surprised to find that the desktop version is a very slick piece of software. To my ears at least, it is perfectly at home beside the more established virtual guitar software plug-ins mentioned earlier. Sonically, therefore, BIAS is most certainly a contender. For complete tone nuts, the ability to dig into your (virtual) amp’s inner workings is going to prove a lot of fun. The fact that the interface makes this so easy to do, and yet still gives you plenty of options, is very impressive.

Equally, in the Professional version, the Amp Match technology is straightforward to use. That said, it is not a magic bullet to emulating the sounds of your guitar heroes; it requires quite a bit of care and attention (and possibly a bit of luck) to match a sound from a favourite track. Matching a real amp is perhaps a more realistic proposition — but that does imply that you might have some amp sounds that are better than the presets built into the software and worth capturing in the first place! It’s clever technology, and very interesting to explore, but perhaps a quite specialist function.

If you just want a versatile amp simulator that supplies a broad palette of pre-configured guitar rigs, its lack of effects means perhaps BIAS isn’t the most obvious choice. However, for true tone-heads, who want to craft how their virtual amp sounds and responds, with the exception of some component editing available in ReValver, BIAS is in a class of its own. In principle at least, the Amp Matching may well appeal to the same crowd. The interface is also a pleasure to use.

The feature set in BIAS overlaps with, but doesn’t mimic, what’s available in the obvious competition. It is well worth auditioning already but, if Positive Grid can add that missing effects element, BIAS will offer both direct competition for the established plug-ins as well as the amp-design element that sets it apart from the herd.


Among rival all-in-one virtual guitar rig plug-ins, Native Instruments’ Guitar Rig Pro, Line 6’s POD Farm Platinum, IK Multimedia’s AmpliTube 3, Waves’ GTR3, Scuffham’s S-Gear and Peavey’s ReValver are probably the most obvious competitors. ReValver 4 is also an interesting comparison because it includes some amp-design and ‘sound matching’ technology. If amp matching is your main interest, the main option is the Kemper Profiling Amp, but this is a hardware unit that is much more expensive than any of the plug-ins.

Matching Up

If you stretch to the Professional version of BIAS, you get Positive Grid’s Amp Match technology. The Amp Matching process is, in principle, pretty straightforward to use, although there are a number of steps involved, and the best way to approach it may depend a little on your specific DAW. In essence, however, BIAS captures an audio sample of your current sound (the source), an audio sample of the target sound, and then applies some processing to ‘match’ the two. The resulting profile can then be applied to the source so that it sounds like the target.

I had a go at matching both a real amp and a tone from a pre-recorded guitar track. Even with a bit of experimentation, the potential of the technology is pretty obvious but, equally, you soon realise that getting good results does require a bit of care. First, in order to make things as simple as possible for the matching algorithm, the closer the sound of the BIAS model that you start with is to the ‘target’, the more likely you are to end up with a good result. Second, you need to make sure that your guitar input signal is as free as possible from hum and noise.

BIAS Professional includes the Amp Match component, allowing you to profile amp sounds and attempt to ‘match’ them within BIAS.BIAS Professional includes the Amp Match component, allowing you to profile amp sounds and attempt to ‘match’ them within BIAS.Third, you want your target sound free of effects — just the sound of the guitar through an amp. This last issue might be more significant when trying to match guitar tones from a commercial guitar track; the trick will be finding a bit of the track where the guitar is both fairly isolated in the mix, and not soaked in delay, chorus or reverb. You can’t get an ideal snippet from all your favourite rock classics, but you can get close with some. I gave this a go with a couple of examples, neither of which were ‘perfect’ candidates, but perhaps typical of what users might like to try. The results were not bad, and I suspect that if I had spent a little more time getting the ‘source’ tone closer to the desired ‘target’ so the matching process didn’t have to do quite so much corrective work, the results could easily have been improved.


  • Very slick user interface.
  • Amp-design features are excellent.
  • Amp Match technology has considerable potential.
  • Sounds very good.


  • No stompbox or rack effects.


Though it’s not quite a complete guitar setup in software, the novel amp-design and amp-matching technology in BIAS will make it very attractive to any serious guitar tone-head.


BIAS Desktop $99; BIAS Professional $199.

BIAS Desktop $99; BIAS Professional $199.

Test Spec

  • BIAS Professional
  • Apple iMac with 3.5GHz quad-core i7 CPU and 32GB RAM, running Mac OS 10.9.5, with Focusrite Scarlett 8i6 interface.
  • Tested with Steinberg Cubase 7.5.20.