In recent years, the market for guitar processors has turned away from rack mounted gear and towards the floor units such as the POD XT Live, Vox ToneLab SE and the Boss ME and GT series. While these devices with their built-in pedalboards make a lot of sense for many guitarists, there are those of us for whom a rack mounted processor is more practical. So it's always a welcome sight to see a new guitar processor that is rack mounted.

The GT Pro is the latest effect and amp modelling guitar processor from Boss, taking the place of the venerable GX-700. It is based on the popular Boss GT-8 floor unit - in fact it is a GT-8, just sans pedals, with added connectivity and housed in a different box.

The sheer number of controls on the front panel is striking, immediately telling you this is a processing powerhouse. There is a similarly impressive array of connectors on the back.

Features
The GT Pro has a huge feature list -probably more than anyone could ever need, but this means there is more variety to choose from. A few of the more important features include:

• 46 different amp models, seven speaker cabinets and five microphone choices.
• Two amplifier channels which can not only be used in the common channel switching arrangement, but can also be combined in a variety of ways.
• 200 preset patches and 200 user patches
• 44 different types of effects - including just about everything you would ever need and a few oddities besides.
• 30 different distortion effects
• Up to 15 effects can be used simultaneously.
• A solo switch, which can be used to boost level and change the EQ of a channel for soloing.
• Software-based patch editor and librarian for Mac or PC.

Hook me up
The connectivity options on the GT-PRO are comprehensive to say the least, including everything a pro studio or stage guitarist could ask for. Aside from the obligatory front panel input and headphone sockets, the well-stocked rear panel includes:

• Unbalanced main outputs and both unbalanced and balanced (XLR) 'Sub Out' outputs. The balanced XLR outputs have a ground lift switch.
• Three send/return loops for connecting external effects processors (one in front of the amp model, two after).
• Two amp control sockets for controlling channel switching of external amplifiers.
• Foot and expression pedal sockets (one of each and a third which can be used for either).
• A USB connector for connection directly to a computer, capable of carrying both audio and control data.
• Digital output via RCA socket
• MIDI in/out/thru
• Built-in power supply.

This all means that whatever your setup, you will be able to connect the GT-PRO to a wide variety of control, amplification and recording systems. The amp control sockets are a nice touch, allowing you to control non-MIDI external devices (such as the channel switching on a guitar amp) and write the setting into a GT-PRO patch. The USB port is a major selling point, being something that the GT-8 does not feature.

It is very nice to see the GT-PRO has an internal power supply as I don't think that any rack unit (especially those calling themselves "Pro") should ever be powered by an external "wall-wart" power supply. While wall-warts help bring down the price of a piece of equipment, they are a problem to secure inside a rack. It also means that you end up with a (usually unshielded) supply inside the rack - often in close proximity to audio cables. My only complaint with the GT-PRO's internal supply is the power cable is permanently hardwired into the GT-PRO, instead of using the more common (and easily replaced) kettle plug power cable.

In Use
The number of controls and connectors on the GT-PRO could appear daunting for some at first. Fortunately however, everything has been ordered well and laid out very intuitively. In fact, the controls pull off the difficult feat of allowing both ease-of-use and powerful control very quickly - thanks largely to the fact that there are so many dedicated switches. If you've ever used any Boss or Roland processor before, it will immediately feel familiar, and you probably won't even need to crack the manual to get up and running.

For those who are new to this kind of device the comprehensive manual has a pictorial "Making the connections" section which makes hooking up the GT-PRO easy. The manual itself is in-depth and contains all the detail you would want - from a short section on turning the unit on to advanced details of the MIDI implementation. The only thing the manual does lack is a "Quick Start Guide" for the impatient.

The optional Roland FC-200 foot controller pedalboard integrates seamlessly into the GT-PRO, and offers more control than you would have if you were using a GT-8 with its built-in pedals. Setting up the FC-200 and GT-PRO to work together is a simple five minute affair, well documented in the manual. Setting up a Behringer FCB-1010 was a bit more complex, but not too difficult and no problems were encountered.

Sound
A/D and D/A converters and internal processing is all at 24 bit 44.1 KHz, so the overall quality of sound is good and there is ample headroom. Signal to noise ratios are not given, but I found no significant noise problems from the GT-PRO itself and the noise suppressor is very good.

Listening to the preset sounds, you could easily be forgiven for thinking the GT-PRO is designed purely for huge, overblown and overprocessed '80s hair-metal sounds. The presets are mostly distorted with very few showing the subtler capabilities of the unit. They do, however, show the extremes that the effects processing is capable of.

Investigating further, stripping a few patches down to basics, I found that the GT-PRO is a capable tone machine. Sounds of amp and speaker models are generally fairly good, if a little gritty and harsh and cover the whole range of amp tones, from crystal cleans through gritty to heavily distorted. The amp models are not perfect emulations of the amps they copy, but seem rather to be designed to give you the correct type of tone while offering a huge range of tone shaping options. So, if you want to create your own unique amp tones loosely based on the classics, it does this very well indeed. However, if you are looking for exact emulations of classic amps, the GT-PRO will not do it as well as some other products. I would imagine that many who are fussier about amp tones are going to be using a separate amp modeller or real valve preamp in one of the FX loops.

The most powerful feature of the amp modelling section is the much touted "dual COSM amp-modelling engine". In simple terms, this means you can effectively have two different amp models at the same time and blend them in a variety of ways. The first method is familiar to anyone who has ever used a two channel amplifier - you can switch from one channel to the other. Where it differs from most amps is you can have two completely different amp models, switching from for instance a Fender Twin type sound to a full-blown Marshall on 11. The other methods get even better: you can layer the two sounds together, similar to using two different amps in the studio. You can either blend them together to create a single mono sound or pan them left and right for a large stereo sound. You can even delay one amp by up to 50 ms, to make the sound even larger and make the two sounds stand apart a little. Finally, you can change from one amp to the other based on your playing dynamics, creating an amp sound which changes from one amp model to another when you play harder.

Another nifty feature is the solo switch which allows you to set a separate volume level for an amp model and change to that instantly for soloing.

The effects section of the GT-PRO is where things really get exciting. Most effects you could want are represented here: There are 44 different effects categories and most categories also have a number of variations - for instance the overdrive/distortion category has an astonishing 30 different types of boosts, drives, distortion and fuzzes. You would be hard pressed indeed not to find just the right overdrive for any need in amongst all this choice. As mentioned earlier, every parameter you would wish to change for any effect is available.

Aside from the common garden variety of effects such as overdrive, chorus, delay, etc., there are a few oddities and specialised effects, some of which are, quite frankly, of limited usefulness, such as the defretter and the sitar simulator. Others are very inspirational, like my new favourite, the slicer.

There are some surprises in the FX section too, with velocity switching also available here - with the added option to control any effect parameter via playing dynamics.

GT-8 vs. GT-PRO
The price difference between the Boss GT-PRO and GT-8 two models is quite steep, with the GT-PRO being the more expensive. So the natural question is: So what are the differences between the two?

They feature identical modelling and effect capabilities. The main differences are the format: the GT-8 is a floor pedal and sports footswitches, while the GT-PRO is rack mounted and has extra connection options (see the table below). The USB connector and the accompanying computer-based editor are really nice extras, but there are already third-party editors available.

It's fairly obvious you are not getting much extra for fair amount of extra strain on your wallet. You really need to look at the differences and decide whether the GT-PRO features are necessary for your application before you choose between the two.

Conclusion
The Boss GT-PRO is a full featured guitar effects processor, sure to make even the most demanding effects junkie happy. It's not as good at emulating classic amps as some other modellers, but the sounds it does create are fairly good and are more tweakable than anything else on the market. Players who want the maximum tone shaping or effect parameter editing will love it, as will those looking for an effect unit to add to their regular amplifier. When compared to its floorboard sibling, the GT-8, it does not fare well, as the GT-8 has most of the same features for a lot lower price, and also has a built in pedalboard.