Line 6 FM4 Filter Modeler Review

With the abundance of effects at our disposal today, we do tend to take all the pedals we have for granted.

There are certain pedals, effects, and products that we might just overlook, despite the fact that they can significantly improve our guitar tone if applied and adjusted properly. You’ll see all sorts of stuff on the pedalboards of famous professional players.

For instance, Kirk Hammett has a whole variety of effects, and you’ll some pretty exciting stuff on there. Over the years, we’ve seen him use Line 6 pedals extensively, including stuff like the DL4 delay. But there’s another interesting effect pedal from the company’s variety of products ñ the FM4 Filter Modeler.

Not kind of a standard pedal that you’ll find in one’s signal chain since it’s actually a modeler, or a “processor” if you will, designed to replicate some well-known vintage filters and synths. So we’ll use the opportunity and dive into this piece of gear and explain a few of its features and what it does.

First of all, for those who don’t know, filter pedals are similar to wah or auto wah pedals. A wah effect is basically a band-pass filter with the center frequency controlled by the rocking part of the pedal.

Or, if it’s an auto-wah, then it’s controlled by the parameters that you set on it. Another great example of a filter would be a talk box. We would recommend though that you inform yourself about filter effects – what they are and how they work ñ before you consider actually getting a pedal like this one.


With filter pedals like the FM4, you can filter out certain frequencies of your tone in various different ways and by using the unit’s different modes.

The pedal itself features 16 different models of vintage synth and filter effects, controlled by the switch on the left side of the front panel. Each of the modes is based on a different vintage filter that was used back in the day by some of those famous guitar heroes.

The pedal also has 20 different factory presets, and you can add your own sounds to the 4 user programmable channels. Each of these saved presets is accessed via the four switches on the pedal.

As for the other knobs, there is four of them and these are all used to additionally tweak the 16 aforementioned models. There’s “FREQ” or “Start Vowel” which controls the start frequency of the filter.

Then there’s “Q” or the “Stop Vowel” which controls the width of the sweep. Aside from these, you have speed, mode or “synth pitch” that changes the band pass, and the “mix” that lets you blend the processed and the clean signal.

The pedal can be used as either a standard mono unit or as a stereo effect since there are two inputs and two outputs on it.

It can additionally be controlled with an expression pedal, which is bought separately. Using the external expression pedal, you basically get endless possibilities in creating your own unique wah effects.

Among other important stuff, the pedal is powered by a standard 9 volt AC adapter.


Looking at this weird shiny purple thing, you’ll definitely not find a pedal like this anywhere on the market.

The FM4 features a casing typical of some other Line 6 modellers and pedals, including DL4 delay, DM 4 Distortion Modeler, MM4 Modulation Modeler, and the JM4 Looper. The casing is, of course, very well built and is quite sturdy.

While it might look like a weird toy lost somewhere in the 1990s, we can’t argue with this pedal’s great aesthetics, build quality, and the overall reliability.


Just to get this out of the way, the pedal works just so damn well. But the abundance of options and features is, at the same time, its main strength and its main weakness.

With a unit like this, you really need to be into the classic vintage filters and guitar synths in order to fully understand the sounds that you’re making.

Some of the effects that FM4 is replicating were used back in the old days by players like Frank Zappa or Robert Fripp of King Crimson.

When it comes to the sound, there’s some really great stuff that you can do with the FM4. Which isn’t a surprise really, since the pedal features 24-bit processing.

By adding the expression pedal, you get a new dimension to the pedal, with various options and features at your disposal.


While it is fun – extremely fun – you’ll have to spend a lot of time tweaking all the knobs in search of your desired sounds. Not that this is necessarily a bad thing since many guitar players enjoy this process.

You just need to bear in mind that this is not exactly the simplest pedal out there. As mentioned, combining it with an expression pedal, there’s a whole new universe of possibilities for you to mess around with and create your own peculiar wah tones.

Looking at the technical stuff, the only downside could be the pedal’s demand for 1200 mA of power. Most of the pedalboards out there, or different power supplies for custom pedalboards, would not support the FM4.

So you’ll need to use its adapter or spend more money on a new power supply. If there is even one that supports this much power.

To conclude – FM4 is a very versatile and exciting pedal to use, while at the same time you’ll need to be somewhat experienced with filters and synths, or at least educated enough about this kind of gear in order to exploit its full potential.

We would not recommend it to a beginner who’s just looking for a flashy and fun new effect unit. Other than that, it’s pretty great.

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