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G-Force M-Tron Pro

Sample Library [Mac / PC]
Published February 2009
By Nick Magnus

The successor to G-Force's popular M-Tron instrument brings dual layers and subtractive synthesis to the Mellotron party — but also manages to keep authenticity firmly in mind...

G-Force M-Tron Pro

Back in the heyday of progressive rock, the mighty Mellotron was the keyboard to own if you dreamed of creating lush orchestral textures and eerie, Gothic atmospheres. It was also very much a luxury reserved for musicians of sufficient financial standing. Fashions changed, however; the 1970s gave birth to string synthesizers, polysynths, punk and disco, as well as a generally dismissive attitude to all things musically 'intellectual'. The Mellotron — along with its notorious unreliability and all its bombastic associations — fell from favour.

When Streetly Electronics went into voluntary liquidation in 1986, it seemed that the Mellotron was to be unceremoniously consigned to the same scrap heap as the wind-up gramophone. However, ardent supporters were still to be found championing the cause, and in the 1990s, prominent artists such as Crowded House, Lenny Kravitz, REM and Radiohead were to spearhead a Mellotron revival. The subsequent resurgence of interest in the instrument, along with the proliferation of affordable samplers, had an inevitable result. One by one, long-neglected Mellotrons were finding themselves being dragged out of their mothballs, dusted down and transformed into sample libraries — either for private use or commercial sale. And why? Because the Mellotron always was, and still is, a fabulous-sounding instrument. Everyone knew it all along, but it took a leap in technology to make its glorious sounds available to, and affordable by, anyone who wanted them.

Then along came VST plug-in instruments, and G-Force were right there in 2000 with the first virtual Mellotron — the M-Tron. This delightfully simple, no-nonsense recreation continues to be astoundingly popular, having found its way into countless musicians' sound arsenals. Eight years were to pass until the next major virtual Mellotron offering (IK Multimedia's SampleTron, reviewed in the August 2008 edition of SOS) — a length of time that's somewhat surprising, considering how enthusiastically the world has once more taken Mellotrons to its bosom. In timely fashion, the long-awaited 'Pro' version of M-Tron was finally announced earlier this year at the NAMM show, bringing a new synth engine, lots of extra features, and a significantly expanded core library.

Recycling Is Good

If you've seen or used G-Force's Virtual String Machine (VSM), M-Tron Pro's user interface will look very familiar to you. Its synth engine is based around the same one used in VSM, albeit with a number of differences that we'll examine in due course. For a full‑blown description of VSM's synth engine, I recommend reading the VSM review that can be found in the May 2008 issue of Sound On Sound. M-Tron uses the same dual-layer structure as VSM, offering two independent sample players, each with its own subtractive synthesis controls. Sounds can be loaded into either Layer A, Layer B, or both. Each Layer features a syncable LFO (for pitch only), a choice of low‑pass, high-pass or band-pass filter with cutoff frequency and resonance, ADSR filter envelope, ADSR amplifier envelope, aftertouch response (to filter) and velocity response to filter and amplifier. The signal chain ends with a pair of global effects that process the sum of both Layers. The two Layers can be edited individually or simultaneously, and the key-range of each Layer can be adjusted to enable 'split' or 'dual' keyboard configurations. Each Layer also has individual level, pan and detune controls, together with a Layer 'solo' function to enable the user to isolate either Layer while editing.

M-Tron Pro can be used as a stand-alone instrument or as a VST, RTAS, AU or MAS plug-in.

M-Tron Extras

The M-Tron Pro's controls are all clearly set out on the instrument's single-screen interface. The red highlighting around the knobs, buttons and sliders indicates that the controls are focused on Layer A. The M-Tron Pro's controls are all clearly set out on the instrument's single-screen interface. The red highlighting around the knobs, buttons and sliders indicates that the controls are focused on Layer A.

In contrast to VSM's global pitch-bend range, M-Tron Pro provides independent bend ranges for Layers A and B, a useful facility lending itself to a variety of psychedelic applications!

Whereas VSM's Layers include a Tune knob (+/- 12 semitones), M-Tron forgoes this in favour of a button labelled 'half speed'. Mellotron aficionados will be familiar with the 'half-speed technique, which entails recording the instrument with the tape recorder running at double speed. When played back at normal speed, the Mellotron's pitch is an octave lower, effectively increasing its lower range and imparting a pleasingly dark, threatening tone. M-Tron Pro's half-speed button replicates this effect by dropping the sample playback speed by an octave. This can be applied to each Layer independently, and produces quite epic results using dual-layered sounds, with the second layer playing at normal speed. Since the range of the Detune knob covers only +/- 50 cents, I would have liked to have seen the +/- 12-semitone Tune knob retained, as there is otherwise no way to offset the tuning of the two Layers by a fixed interval without recourse to using (and holding) the pitch-bend lever.

The 'Tape Rev' button is also specific to M-Tron Pro, and is fairly self-explanatory — it plays the sounds backwards! While this may not seem especially beneficial when applied to sustaining sounds such as strings or choir, its usefulness becomes immediately apparent when applied to 'one‑shot', non‑sustaining sounds such as piano and guitar. M-Tron's library of rhythm phrases, Optigan phrases and sound effects also provide plenty of scope for reverse playback, with suitably bizarre and surreal results.

Another feature specific to M-Tron Pro is the Att-St knob. This is used to adjust the sample start point, which has several very useful applications. Firstly, it addresses one debatable criticism of the original M-Tron, which was the way in which the beginnings of certain sounds seemed too 'clean', exhibiting little or none of the distinctive key-on 'spit' characteristic of tapes whose start points have been poorly aligned on the tape frame. While arguably undesirable, this 'spit' imparts a powerful, aggressive edge that contributes greatly to the Mellotron's gothic personality. Adjusting the Att-St knob on M-Tron Pro, however, allows the user to 'misalign' the tapes by anything up to seconds. Choirs can be made to bark, and strings to spit — you'll be wanting to keep some dog biscuits and a spittoon nearby.

Another popular trick employed by Mellotronists is to double-track the instrument to create a lush, stereo soundfield. The Att-At knob allows you to simulate this to great effect. Simply load the same sound into both Layers, and advance the start point of one Layer by the smallest amount — just one or two increments will do the trick. Pan the two Layers hard left and right, and there you have it — a blissfully lush Mellotronic panorama. Detuning one Layer by a few cents adds even more fullness to the sound, without any unwelcome phasing effects. A subtle variation on this theme is to reverse one Layer (assuming you're using a sustained sound such as strings) and use the Att-St knob to trim any 'dead air' off the end of the reversed Layer, so that it produces sound immediately when keys are played. Reversed one-shot sounds that include some 'dead air' at their ends also benefit from offsetting the start point, enabling you to fine-tune their lengths more predictably. My only criticism here is that the offset range could do with being rather larger than seconds, particularly when applied to reversed one-shot sounds. Being able to play just the first second or so of a sample in reverse would be especially useful.

MIDI Controllers

Like VSM, M-Tron Pro provides MIDI control over virtually every parameter. Clicking on the MIDI CC button darkens the control panel, displaying red, green or grey squares around each controllable parameter. Red squares apply to Layer A, green to Layer B and grey to Global parameters. To assign a MIDI controller, click the appropriate coloured square, move the desired knob, fader or button on your MIDI controller, and the assignment is done. Assigned parameters display the chosen MIDI controller number in white. To un-assign any parameter, simply point to its square and Ctrl-click. A single MIDI controller can be assigned to multiple destinations, so dramatic changes can be effected using just one knob or fader. It's not possible to set the operational range of each controller, which is a shame. Nor can you invert the response to incoming control messages, so crossfading between Layer A and Layer B, for example, can only be done using two independent controller curves, one for each Layer's level.


The M-Tron Pro in MIDI control assign mode. The red squares denote Layer A controls, the green squares Layer B controls, and the grey squares Global parameters.The M-Tron Pro in MIDI control assign mode. The red squares denote Layer A controls, the green squares Layer B controls, and the grey squares Global parameters.

M-Tron Pro is equipped with two global effects, Delay and Ensemble. The Ensemble effect is identical to that found on VSM, modelled on the bucket brigade-type multi-voice chorus typical of vintage string ensembles. This features wet/dry mix, a choice of two, four, six or eight chorus voices and a voice detune control, but no speed parameter — the chorus speed is preset to run quite slowly. However, if the fast, tremulous variety of ensemble is what you're after, I discovered a rather neat donationware plug-in called String Chorus that does a fair job of emulating the classic Solina/ARP Omni ensemble effect. It can be downloaded from The stereo Delay effect features wet/dry mix, separate left and right delay time and feedback controls, and a 'crossfeedback' button. A Sync button locks delay times to your host DAW's tempo. When running unsync'ed, delay times are shown in milliseconds if you hover the mouse over the control, and when sync'ed the times are displayed as note values. The 'faux stereo' Width button found on VSM is not included on M-tron Pro, as dramatic stereo effects can be produced using the techniques described earlier.


The fact that Streetly Electronics are back in business building new Mellotrons is testament to the enduring popularity of this keyboard classic. However, those of us unable to stretch to the heady cost of the real thing may be confused as to which of the two current virtual 'Tron frontrunners — M-Tron Pro and SampleTron — is right for them. The choice could arguably be determined by whether you are an experimentalist or a traditionalist. If you are of the former persuasion, you may be drawn to certain SampleTron features that enable you to defy 'Mellotron conventions' in various ways, such as time-stretch (which gets more mileage out of the rhythm and phrase-based material) and the larger complement of effects. Traditionalists, on the other hand, will be primarily concerned with recreating 'essential' Mellotron sounds to a high degree of authenticity. M-Tron Pro caters for both schools of thought, while at the same time retaining a faithfulness to the original instrument at its heart. There are enough tools to subvert the sound in imaginative ways when required, as well as its own unique features, such as reverse playback and adjustable sample start point, and a highly accessible front end. With its improved functionality, dual synth sections, expanded library and a continuing emphasis on authenticity, M-Tron Pro could well become as ubiquitous as the original M-Tron.  


Here's a quick list of some of the other Mellotron sample libraries currently available:


IK Multimedia SampleTron (VST instrument); Sonivox Mellotron Vintage Synth (VST instrument: Strings, Choir and Flute only); Hollow Sun NewTron Bomb (sample set for Kontakt, Akai, etc).


Batsounds 'MellowSound' (VST instrument: three Violins, Mixed Choir, Brass); Dream Vortex Studio 'Nanotron' (VST instrument: String Section, Male/Female Choir, Flute); Tweakbench Tapeworm (VST instrument: Strings 1, Strings 2, Mixed Choir, Brass, Flute); Taijiguy Mellotron (sample set for SFZ players: three MkII Violins and MkII Combined Brass).

The M-Tron Pro Library

The core library consists of 194 Tape Banks, including all 103 from the original G-Force M-Tron. The new material includes 45 previously unreleased Tape Banks, plus 40 looped varieties and 19 remastered ones. Amongst the new sounds are Hofner bass, solo trumpet, a selection of Optigan rhythms, custom choirs, custom sound effects, Danelectro and Gibson guitars, additional saxophones, and a number of new string and orchestral sounds. The Tape Banks are organised into instrument categories, so finding specific sounds is as straightforward as possible. In addition to loading the basic Tape Banks into Layers, M-Tron Pro also provides a large library of 886 Patch Presets, also organised by instrument category and guest programmer (whose number includes Rick Wakeman), showcasing many creative applications of its synth section and effects. Of course, any creations of your own can be saved into a dedicated User folder, within which you can create subfolders to help organise your own patches.

The Remastered Tape Banks

G-Force chose 19 Tape Banks that they felt would benefit from some loving TLC in the form of remastering. This was performed at Abbey Road Studios under the expert care of resident mastering engineer Steve Rooke. The Tape Banks were re-recorded through a vintage EMI TG12410 analogue mixing desk, using a Prism Maselec Equaliser and an EMI compressor. While always mindful not to destroy the vital character of the sounds, they took the opportunity to retune and repair the occasional suspect note. G-Force are laudably concerned with authenticity, and while the remainder of the library (where appropriate) retains the Mellotron's natural eight‑second playback limit, the remastered sounds are alternatively presented as looped versions. This, the manual wryly states, along with stern warnings against inappropriate use and bad taste, is to appease 'non-purists' who requested the feature.

Owners of the original M-Tron plug-in should note that M-Tron Pro is a totally new program, and not an upgrade — so you'll need to keep the original library and the plug-in installed alongside this new version if you'll be wanting to run older projects that used M-Tron.

Published February 2009