GForce Software M-Tron Pro IV first look review and sound demo Popular Mellotron plugin got a makeover with new features, UI, and more.

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Review: GForce Software M-Tron Pro IV plugin is a major step forward for its popular take on the Mellotron M400 with new features, interface, and sounds.

Next to synthesizers, the Mellotron is one of the most influential keyed instruments in music history. Whether electronic music or prog-rock, it was everywhere. Also how it worked was for the time very unusual and futuristic. It used the same concept as a sampler but generates its sounds using analog samples. These were recorded on audio tapes.

Today, in a time where we get everything digitally, there are also Mellotron emulations for your DAW. One of the most popular is the M-Tron Pro from Dave Spiers and GForce Software. This is available today in a new M-Tron Pro IV version. Thanks to GS for providing me with a version for testing in advance.

GForce Software M-Tron Pro IV

GForce Software M-Tron Pro IV Review

Disclaimer: I don’t have an original Mellotron in the studio myself and have never had the opportunity to work with this legendary instrument for a long time. So I can’t make any comparisons between hardware and software.

This is a first-look review because I didn’t work with the plugin for months but only for a limited time. A complete review requires long-term experience, etc. Plus, the IV is not a completely new plugin but a major upgrade.

M-Tron Pro IV

With the M-Tron Pro IV, GForce Software continues its popular Mellotron M400-inspired plugin. The work they put into this plugin is comparable to the other releases from 2022 and 2023 like the Minimonsta2 or Oddity3. Not a revolution but an evolution.

The plugin is the same in many points as its predecessor but has been upgraded with new features. Let’s start with the one that immediately catches the eye.

GForce Software M-Tron Pro IV

New UI

Yes, GForce Software boosts the M-Tron Pro with a new fully-scalable UI in the fourth version. One that significantly upgrades the plugin and makes it look more modern and elegant. I particularly like the synth layout of the parameters. The old UI had a more bulkier look.

M-Tron Pro IV UI

You can also benefit from a new powerful preset and tape browser sorting your sounds and sources in available collections, categories, and more. It also shows the patch author, the used sound sources for the chosen patch, and more. You can also leave a heart behind your favorites. The new browsers are very intuitive to use and give a nice overview of the included sound content.

At first, I had problems that the sounds were not displayed. That was probably because of the order of the installation. Install first the sound library then the plugin. If you follow this order, it should work as expected.

Upgraded Engine

The engine also benefits from this IV makeover. It still uses the same dual-layer architecture but with some solid additions. Unlike the Arturia Mellotron-V, the M-Tron Pro is less of a hardware emulation.

Instead, it uses multi-sampled sound sources recorded in very high quality from Mellotrons. Thus, version IV is still limited to the sources that GForce supplies in the factory library or sells separately as expansions. So no custom samples i.e. nope your intergalactic farts will not enter the Mellosphere. Two different approaches to bring Mellotron sounds and charm to DAWs.

GForce Software M-Tron Pro IV

Two slots (A/B) per patch, each containing a selectable sample-based sound source. There are nearly 200 sample sets (tape banks) available in the factory library. They range from Mellotron-infused basses, leads, pads, strings, …. and of course choirs. Months of fun are guaranteed.

The clever color coding of the predecessor has remained. Green is layer 1, red layer 2 and in link mode the knobs become blue. This allows you to edit each layer separately or together. Plus, you can create splits for mapping two different sounds on the keyboard.

Wow And Flutter

There are five sound-shaping blocks per layer. It starts with the TAPE where you can perform sample/tape set edits very easily. You can tune (-12/+12) or detune your timbre. A new feature in M-Tron Pro IV is wow and flutter with rate, instability, and rate controls. This allows you to age tape sets to make them sound more authentic to the past. A time when nothing was 100% stable and in sync.

Set everything to maximum and the whole thing starts to wave or swim. Up to 1/3, you get nice subtle effects to make it sound more organic. There are also options to reverse and half-speed the tape. Great for more advanced sound designs that go beyond classic Mellotron timbres. Reverse works great with one-shot sources.  Also, it has an attack start, pan option, and level control.

Filtering & Modulation

Then, you can work with a new expanded multi-wave LFO with flexible destinations: pitch, filter, pan, and level. Four targets are a bit tight, more would be desirable. Also, a second LFO would give more modulation flexibility. However, I particularly like the addition of the fade-in function, handy for delayed modulation effects.

The self-resonating filter for each layer with its own ADSR envelope is also onboard again but in an expanded setting with an all-new smooth state-variable filter. It’s probably the SVF from their excellent Oberheim plugins. Fits very well with the old Mello sounds. Next to this is again a classic ADSR envelope.

GForce Software also added a new performance section in each layer giving you control over the velocity, bend range, and aftertouch (mono & poly). It’s a pity that you can’t route this very flexibly. They are limited to two parameters each.

GForce Software M-Tron Pro effects

Big Effects Boost

Effects serve to round off sounds and finalize them. They can also catapult sounds in new directions. I think GForce had both in mind. Where yesterday’s M-Tron Pro only had classic delay and ensemble, the M-Tron Pro IV has its own beefed-up multi-effects processor.

Layer A, B, or both in the effects? That’s the decision you have to make before opening the gate to the effects. There is only one effects line, it’s not possible to have different effects per layer. There are amp/distortion, delay, ensemble, and reverb available. Their signal path is, however, fixed and not adjustable. It would be nice if you could move them like modules. And modulation of the effects is also not possible.

The first effect in the signal chain is an all-new amp simulation with warmth, noise, and saturate parameters.  This is about bringing character to the sound. It can go from slight distortions/heat for additional warmth up to crunchy, noisy, dirty timbres in extreme settings.

Then it goes into a stereo delay with L/R control and cross-feedback + sync options. Classic in the standard settings and with higher you can achieve very atmospheric, endless delays. Before going into the reverb, the signal path makes a detour into a two-mode 8-voice ensemble effect with detune and mix control. This sounds solid, nothing revolutionary but the way an ensemble effect should sound: adding richness, width, and movement.

The last step is the new matrix reverb module. An excellent sounding, atmospheric reverb we already know from the other GForce software synths. The new FX parameter locks are also a useful addition.

M-Tron Pro IV

What Else?

Besides these major new features, M-Tron Pro IV also comes with an extended keyboard range (down seven semitones), new useful utilities (undo, redo, copy, and paste), programmable MIDI CC response via MIDI learn, and more.

On the bottom left are the well-known macros for volume, tone, and pitch. On the right are two intriguing additions selectable via simple on/off buttons. There is rewind for the tape but also a function called “The Brake”. Once activated, it slows the tape playback speed allowing you to create pitch-shift effects. These are not very dominant but rather subtle and beautiful in the sound.

Sound Content

There is little new to say about the sound content of M-Tron Pro IV. GForce ships the plugin with an unchanged premium quality library of over 3.5GB of samples. It gives you nearly 200 total tape banks/sample sets for the sound slots.

From this core library, the GForce Software sound designer team has created over 800+ presets and performances, including 100+ new presets for the IV version. These sound very high quality and beautiful. Very varied from very classic Mellotron choirs and strings to very bizarre and extraordinary. The presets give you a huge overview of what is possible with the plugin. And don’t forget, it’s just an appetizer because you can also create your own sounds with it.


The M-Tron Pro IV sounds great and fat. When testing I was surprised that all this uses very little CPU. Ok, I have an M1 Max but the CPU bar in Ableton Live 11 never went above 15% which is very little. That’s a big plus point.


The new M-Tron Pro IV is a worthy successor to the previous M-Tron Pro. It sounds very authentic to me and is strongly reminiscent of the well-known Mellotron sounds. Having never played or worked with an original, I can only compare it to sound demos and recordings.

However, the many classic sounds of the M-Tron immediately pushed me into the vibes of the original Mellotron. This smoky, lo-fi charm is right there and takes you back to the 70s and 80s. The new features fit the engine perfectly. Especially the wow and flutter bring even more vintage mojo into play. The new effects, especially the distortion is an excellent addition to give everything more crisp and warmth.

​I have two points to criticize. This is my point of view, but I could be wrong. I would like to have more modulation options as well as a modular-style FX chain where I can rearrange the FXs. It would give me more flexibility. Yes, M-Tron Pro IV still not supports custom user sample sets. This is due to the engine choice and not a criticism. I hope, however, that future versions will be more open here.

All in all a solid, money-worth upgrade As said at the beginning. Not a revolution but an evolution of the popular M-Tron Pro plugin by GForce Software.


  • intuitive, super easy-to-use UI with a more clear and modern layout
  • hassle-free preset and sound browser
  • expanded tape with wow and flutter
  • high-end sample content with Mellotron rarities
  • new effects (amp, reverb…)
  • low CPU consumption


  • not a 100% Mellotron emulation
  • no custom samples


  • modulation limitations (single LFO per layer, limited destinations (LFO, velocity, aftertouch…)
  • fixed effects signal path

GForce Software M-Tron Pro IV is available now for an introductory price of £74,99 + VAT instead of £149,99 + VAT. It’s also available as part of the M-Tron Pro IV Complete bundle for £333 +VAT.

Existing customers of M-Tron Pro can upgrade for £29.99 + VAT. It runs as a VST, VST3, AU, and AAX plugin on macOS (Intel + native Apple Silicon) and Windows. 

More information here: GForce Software 

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