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Terratec Axon AX50 USB

MIDI Guitar System By Paul White
Published October 2007

Is this the perfect marriage of guitar and MIDI?

Terratec Axon AX50 USBAxon's claim to fame is that they have the fastest-tracking MIDI guitar system currently available, and one that is fully compatible with the Roland GK, or any similarly-specified pickup (though the pickup itself is not supplied with the Axon hardware). Top of the range is the Axon AX100 MKII, which includes a MIDI sound source and has extensive programmability via both the front panel and the included software.


The new Axon AX50 USB is based on exactly the same core technology as the AX100 and, though it is simpler, it still offers an impressive degree of editability via USB. New connection options for electric and acoustic guitarists, bassists and violinists add to the flexibility of this device and its MIDI output can be transmitted over USB (though the conventional MIDI In, Out and Thru sockets are still there), which means that no additional MIDI interface is required.

Depending on the facilities offered by the host software, more adventurous users can control an external instrument and up to four software synths simultaneously. Editing via MIDI is no longer supported, so USB must be used for computer editing and, in effect, the USB port functions as four virtual MIDI ports, which can be configured within each user preset you create. A rear-panel output jack is also provided for the direct sound from the instrument, which can be used if your instrument has been connected to the guitar input of the GK pickup being used with the system. All the button and control functions on the GK pickup system are recognised and transmitted by the Axon hardware, allowing volume change, patch changes and so on to be controlled from the guitar.

Rather than wait for a whole cycle of audio to pass in order to ascertain its frequency, the software uses Early Transient Recognition, which is based on neural net technology. This identifies the pitch of a note based on the characteristics of the picking transient, which in turn allows the correct MIDI note to be sent with minimal delay. After this, conventional pitch-tracking takes over, so that pitch bends and vibrato can be followed correctly (assuming, of course, that pitch quantisation is switched off for the current patch).

The AX50 USB also enables more adventurous players to divide the guitar fingerboard into up to 12 different zones, based on string and fret number. The manual lacks good, practical examples but, for example, each zone may be used to control a different sound. Axon's technology can also sense pick position along the string, and this information may also be used to define zones, or can be linked to MIDI controller information to create position-dependent tonal changes. It is hard to imagine how all this is possible from a tiny box with no obvious controls, and only a simple numeric display on the front (the nearest thing to a control is the Tuner button, which turns the numeric display into a guitar tuner). The secret, of course, is that for anything more than plug-and-play guitar-to-MIDI conversion you use the editing software on your PC or Mac. Patches are created that contain the parameter and zone information, and these can be stored in one of 128 patch memories on the Axon hardware.

Unlike its larger sibling, there are no in-built sounds with this model. Instead, you get a copy of Terratec's Producer's Wave Xtable VI, a 64-part multitimbral soft synth that offers the full set of 128 General MIDI sounds, as well as nine drum kits and effects. It is a sample-based instrument that uses Native Instruments' Kontakt Player as a front end and runs with Audio Units, VST, DXi and RTAS hosts, as well as in stand-alone mode.

Useful USB

Once the unit has been connected to the computer (I used a Mac G5) via USB and the software installed, you need to make a connection between the hardware and software via a button on the editor page. Once the hardware has been recognised, you can transfer patch information from the editor to the hardware or vice versa. A crucial step — no matter how simply you intend to use the system otherwise — is to set up the string picking sensitivity on the Global page to suit your pickup position and your playing style. The aim here is to get an even picking response across the strings, where the sensitivity is high enough that you don't miss any quietly picked notes, but not so high that fingering noise throws up false notes. You can also set a separate note-on and note-off threshold. Six sliders control the sensitivity of individual strings but, from what I can see, it seems that adjustment is done by ear, since there's no metering on screen (as there is, for example, with Roland hardware). The Global page enables you to store settings for up to eight different GK-equipped instruments.

Though the hardware looks pretty simple, there's plenty of flexibility offered by the bundled control software.Though the hardware looks pretty simple, there's plenty of flexibility offered by the bundled control software.One important setting that you need to adjust on a per-patch basis (on the Preset page) is the pitch tracking, which can be set to quantised (chromatic) or to follow the string pitch, using MIDI pitch-bend. If you want to use MIDI pitch-bend, then you must ensure that the pitch-bend range you set in the patch window matches that set for the external synth or soft synth you're controlling. Moreover, if the synth being controlled is set to a single MIDI channel, using Poly mode, you can only use string-bending when playing monophonically. An Auto mode forces this 'bend only one string at a time' behaviour when you're working across six MIDI channels, which can be useful where you need chords to be dead in tune but still have the flexibility to bend notes during solo parts.

To get the maximum flexibility for string-bending, you need to use MIDI Mode 4, where the synth behaves as six separate monophonic synths, assigned to separate MIDI channels. This can be a bit of a chore on some DAWs, which is why I keep petitioning for more guitar-friendly features, such as dedicated MIDI guitar instrument tracks. These could have their own preferences, so that whenever a soft synth is inserted into a MIDI guitar track, its six MIDI channels and bend range would automatically be set as per the user preference — with a bend range of 12, allowing you to bend or slide anything up to an octave. Until we get this in all the popular DAWs (and, to their credit, Cakewalk have made inroads with their guitar version of Sonar), MIDI guitar users will always have to jump through a few hoops to get the best out of their instruments.

In Use

Most of the instruction manual is presented as a PDF file. If there's a flaw it is that the manual is rather too shallow, but it also seems to assume a decent working knowledge of MIDI, rather than leading the guitarist by the hand a bit more, as it easily could have done.

Although it is useful to have a good GM sound set included with the instrument, I feel that most MIDI guitar players will be on the lookout for something more ambitious, so it would be wrong to judge the Axon AX50 USB based on the included sound set: that's not really what it is about. Rather, I think players really care more about the practicalities, and specifically about whether the device can track what they're playing without introducing delays or false triggering — because without that, the ability to set up fancy zones or obscure MIDI controller functions becomes pretty meaningless. One practical issue is that the 13-pin DIN connector for the GK pickup is positioned on the front panel and doesn't support the cable very well. During my tests I had two strings suddenly refuse to play, and I traced the cause to the front-panel connector working loose. Clearly, this could be very embarrassing during live performance!

To obtain good results from the AX50 USB, you need to take care setting the pickup height to get the recommended string spacing, or very near it, then you need to set the string sensitivities as carefully as you can to suit your playing style. It's also a good idea not to set the guitar action too low, as MIDI guitar systems don't respond well to fret buzz or choked notes.

As well as the USB and MIDI connections, there's a jack on the rear panel for outputting the direct sound from your guitar.As well as the USB and MIDI connections, there's a jack on the rear panel for outputting the direct sound from your guitar.Once setup is complete, the tracking speed is impressive, with no discernible delay even on fast passages — unless you choose a sound with a slow attack, of course. As with any other pitch-tracking MIDI guitar system, you need to play cleanly, watch how you lift your fingers from the strings (so as to prevent your action being interpreted as a deliberate hammer-off) and avoid, at all costs, the temptation to 'dig in' to the notes to produce harmonics. This is something that many rock players do without thinking, and if you do it, you should expect the unexpected! In fact, the limit to speed on this system is not the tracking speed but how fast you can play while still playing cleanly.

One thing that I really missed on this model was a socket for a Hold footswitch. Using Hold to sustain notes or chords past the natural decay time of the guitar strings is an integral part of MIDI guitar playing, and while you could use a separate MIDI pedal or keyboard controller to achieve this, it makes far more sense to have one built in, as Roland do on their GR models. Furthermore, as the display is only a simple number, it would at least have helped to have some kind of indicator LED to show whether the patch currently selected was pitch-quantised or set for pitch bend. Those issues aside, the AX50 USB is hard to fault, particularly in the light of the performance limitations of other current pitch-tracking MIDI guitar technology. You do have to clean up your playing style and play appropriately to the sound you're using, but that's just the nature of the beast.

The zoning functions are more comprehensive than offered by any other MIDI guitar system I've tried, and the pick position sensing is, as far as I know, unique to Axon. One of the frustrating things about MIDI guitars is that they fail to translate the majority of the playing nuances that a guitarist uses during the normal course of playing, which in turn robs the sound of a sense of performance. Being able to introduce tonal changes by having the pick position send MIDI controller data is a useful way of getting back at least some degree of control over the sound during performance and is to be welcomed. It also works surprisingly well, although, as I mentioned earlier, the manual doesn't provide any practical examples of how this might be set up. Zones can be individually transposed and routed to either the MIDI Out or any of the four virtual MIDI ports afforded by the USB connection. MIDI is transmitted on six consecutive channels, and the base channel can be set by the user.

I should mention, for the sake of completeness, that I experienced a few problems using the system within Logic —though I think these are issues with the installation of Logic (or possibly other software) on my machine, rather than a fault with the Axon. I couldn't get any MIDI data from the Axon into Logic unless I trashed all my Logic Control setup, after which it sprung to life. Thereafter, the channel fader of the instrument I was controlling had a habit of switching itself off, or to maximum level — sometimes as a result of me strumming, but more often when I changed between pages in the editor software. There was also a slight tuning discrepancy between the guitar and the synth sounds, even though the front-panel tuning indicators said I was spot on. However, one of my colleagues at SOS tried another AX50 USB with his own system (also a Mac G5 running OS 10.4.8) and experienced none of these problems, though he did report that the editor software occasionally lost contact with the synth, meaning that he had to press the Connect button to restore operation. He was also using Logic Control and didn't need to change any settings to get it to co-exist happily with the the AX50 USB. To make sure, I tried the tests again a few days later, and this time the Axon seemed happy to work alongside Logic Control, though the odd erratic fader moves and the small tuning discrepancy persisted.

Signing Off

Though not hugely cheaper than its more complex sibling, the AX50 USB is much more guitarist-friendly and, once you've set up your own patches using a computer, you can easily take it out to use live, using the buttons on your GK pickup or instrument to select the user presets. Most guitar synths work best with their own internal sounds, and while this Axon is a MIDI-only device it controls external synths rather better than its competitors. The only real practical weaknesses (not counting the inexplicable and inconsistent Logic foibles), other than those common to all MIDI guitar systems, are the lack of a Hold pedal input jack and the rather unreliable 13-pin connector on the front panel. However, I did feel that the manual could have been more helpful in guiding guitarists through the more advanced features of the system.

As a studio tool for guitarists, the AX50 USB is a great way forward. In fact, even if you normally play keyboards you may find that it helps your writing process, as you tend to generate very different musical ideas when using a guitar. Using a pitch-tracking MIDI guitar system will always be frustrating in comparison to playing the guitar normally, but the Axon system is about as good as it gets, and in the right hands can sound fantastic. If you're prepared to clean up your playing, with a little perseverance you'll soon be producing great-sounding results. 


Though there are a few options for the MIDI guitarist, the only direct competition to the Axon range comes from the Roland GR33 and GR20.


  • Fast, accurate tracking.
  • Simple to use on a basic level.
  • Some useful 'more sophisticated' features are available if you need them.
  • Using the on-screen editor is simpler than doing everything from a front panel with a tiny display.
  • Good quality GM sound set included.


  • A computer is essential for setting up and editing.
  • No Hold switch input.
  • 13-pin GK socket not reliable.
  • Manual thin on practical help.


The Axon AX50 USB has all the tracking attributes of the larger Axon AX100 MKII, plus USB connectivity, but it is less complex. It lacks the internal sounds, but controls external synths better than its competitors. It requires a computer to set up or edit via USB, but once set it can function as a stand-alone unit.


£319 including VAT.

SCV London +44 (0)20 8418 0778.

+44 (0)20 8418 0624.