xfilter
The Universal Equalizer

xfilter

4-Band Analog Stereo Equalizer

Link Me Up

The xfilter is a true linked stereo equalizer with the heart and soul of our flagship EQ, the museq. It gives you the expensive sound of an all class-A equalizer in a surprisingly affordable package, with a precise stereo image based on computer-selected, stepped pots and low tolerance film caps.

5 reasons why you should use the xfilter

even there are many more!

Build Quality
The xfilter, just like all our products, is designed, engineered and handcrafted in Germany.
Class-A Topology
Consequently represents the art of discrete signal processing.
True Stereo Link
As one of the few exceptions in the market, the xfilter processes both of its channels with just one set of controllers – a true stereo linked EQ.
Computer-Selected Potentiometers
Every single dual and quad layer pot we buy is measured with custom computer routines, and only the lowest tolerance ones go into production.
Low Tolerance Capacitors
The special series of film caps used for the xfilter performs twice as good as the industry standard in terms of component tolerance.

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Build Quality

The xfilter is all about details.

Every single of its many aspects – sound, features, circuitry, components, design, materials, manufacturing – has been thought over and over until there was just nothing left to improve. Basically, every single part of our fine products is custom, and most of these are made according to our own designs and specs.

Only the best components the market has to offer are good enough for the xfilter, and it shows. Each of our product is manually built to order and tested by ourselves, here at our headquarters in Germany.

Our product benefits sum up in an audio quality that is beyond all doubt. Even when extreme settings are used, the sound always stays clean and powerful.

Massage Included

The xfilter is absolutely serious about flexibility. It offers high and low shelf bands which can be switched into high and low cut filters with resonance, two mid peak filters with wide and narrow Q, plus additional passive LC stages with shielded coils for a glorious top end.

With its exceptionally open sound, straight transient projection and solid punch, the xfilter is the perfect match for your xpressor – or any other piece of delicious outboard gear!

True Stereo Operation Resonance High & Low Pass Filter Switchable Filter Quality Additional Passive High-Band Stepped Controllers

True Stereo Operation

Using an analog EQ on a stereo buss can be quite tricky, as only very few units offer the possibility to link their two mono channels for true stereo processing.

As a result, the user needs to fiddle around with many knobs in order to cope with the tedious task of matching the settings for both channels as good as possible. The problem gets only worse when the controllers do not have any steps for reference.

But while there are so many compressors in the market that can be linked for stereo operation, why are there almost no EQs which can do this, too? One of the main answers is component tolerances. Obviously, you want the two linked channels to behave exactly the same, but the natural tolerances that especially potentiometers and capacitors have counteract this ideal characteristic.

To make a long story short: The xfilter solves this problem by using computer-selected dual and quad layer pots as well as special low tolerance caps.

Resonance High and Low Pass Filter

The outer bands of the xfilter show a great amount of flexibility. In their standard mode, they are set up as sweet sounding high and low shelf filters that can be used to tailor the airiness and fundamentals of your tracks fast and efficiently.

As a special feature, you can independently switch these to become high and low cut filters with 12 dB per octave and an additional resonance peak at the knee frequency. This allows some very interesting and useful filter curves.

Especially bass frequencies can benefit from a low cut with resonance by obtaining a clean and punchy character. But the resonance can also be used to stretch signals in the bass range, because the resonance filter causes a longer post-oscillation time.

In the high frequency range, you can use the resonance filter to put an accent on a selected frequency without boosting the complete HF spectrum at the same time, which can prevent harshness or an unwanted shift of the overall perception towards the treble.

Switchable Filter Quality

The filter quality of the two parametric mid bands can be switched between two characteristics: Wide (Q 0.5) and narrow (Q 1.0), based on the proportional Q principle.

When designing a parametric filter, you have quite a range to choose from when it comes to the Q factor. After extensive listening, we decided to implement a choice of 0.5 or 1.0 in the xfilter, as these parameters always result in what this machine is focused on: Very musical processing.

You will notice that very narrow Q factors are not offered here. These days, most engineers we know of use digital filters for notching narrow ranges to get rid of problematic frequencies anyway. And this is for a good reason, as it works extremely well.

Additional Passive High-Band

Mmm… The incredible magic a passive EQ can add on top of everything. We all love it, we all need it!

Well, here is the good news: In addition to its four flexible active bands, the xfilter features a switchable fixed LC filter for polishing the high frequency range. The filter mainly consists of a capacitor and a coil per channel, but unlike the standard shelving designs, it has a slight resonance peak at 12 kHz and starts to fall of at 17 kHz.

This way, the saturation-like storage effect of the coil focuses on the area around the peak without pushing the complete high frequency spectrum too much. The inductors used in the xfilter have their own shields to reduce outer influences like hum – without these shields, the coils would pretty much act like antennas for all kinds of unwanted noises.

Now you know what the ‘Passive Massage’ is all about: Opening up the top end of your signals by pushing just a single button!

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Stepped Controllers

The xfilter features stepped potentiometers for all its parameters throughout. The 41 steps make a precise recall very easy, and they provide a useful range of possible settings at the same time. And you will just love the feel of them, too.

Stepped controllers are something you will usually only find on much more expensive gear, special mastering editions, or in most of the cases – not at all. The xfilter establishes this very handy feature in the regular serial version without any luxury up-charge.

Computer - selected Pots Low Tolerance Capacitors Ground Layer Shield Discrete Class-A Technical Data

Computer-Selected Potentiometers

In a linked stereo EQ, the potentiometers need a lot of layers. The pots for setting the mixers (gain) have two layers each, while the pots for setting the frequencies even have a total of four layers each!

The problem occurs that every single layer has its own component tolerance, and while layer A could be at the absolute minimum of the allowed tolerance, layer B could be at the absolute maximum. As a result, the filter stages of the left and right channels would not behave the same.

To solve this, every single potentiometer in the xfilter is measured and selected with an Audio Precision rig and computer routines written exactly for this task. As a result, only 65% of the dual layer pots and only 50% of the quad pots we buy go into production – the rest is put aside.

It’s a true custom shop option we are proud to offer with every xfilter free of any up-charges.

Special Low Tolerance Capacitors

If you look under the hood of an audio equalizer, it is very likely that you will find a lesser or greater number of film capacitors. These caps use an insulating plastic film as the dielectric, which is drawn in a special process to an extremely thin thickness.

There are several technical reasons why film caps are a good choice for audio filter circuits, and generations of audio engineers will confirm that they sound great, too.

A typical representative of this component is the MKS film type, which is a great sounding cap to be found in many EQ designs. However, many MKS types come with a typical tolerance of 10%, which can have a negative influence on the channel accuracy of a stereo linked EQ.

For this reason, the xfilter uses a special FKS type film capacitor which sounds just like a good cap should, coming with a maximum tolerance of 5% only. One more step towards a more accurate stereo image.

Ground Layer Shield

The PCBs of the xfilter have a total of four layers: Two of them are used for the audio circuitry, one is for power supplying traces, and the last one is a dedicated ground shield layer. But what’s the idea behind this?

The filter networks of the individual bands of the EQ become higher in resistance the lower their specific frequency is set. This makes them more vulnerable towards hum which is caused by electric fields.

As the additional ground layer is placed extremely close beneath the traces which carry audio, it is very efficient as a shield against unwanted noise interferences.

Discrete Class-A Topology

We love the sound of class-A circuitry! And here is why: In a class-A amplifier, the transistors are conductive all of the time, so there is no crossover distortion at all. This is the perfect technological basis for an open sound with massive punch and no degradation of your original source.

The discrete approach makes it possible to design every single stage in signal processing exactly to what you want it to do – physics becomes the only limit. The xfilter uses our custom discrete input and output stages derived from the alpha compressor. The mixing stages are also discrete designs running in class-A mode.

The actual filter stages (band pass etc.) use integrated op-amps instead, and also in this regard we did not go for an off-the-shelf solution. Instead of cheap industrial standard op-amps, the xfilter uses high grade Burr-Brown OPA series amps which have been designed especially for the critical discerns of pristine audio circuitry.

And there it is – the expensive sound of boutique high end EQs in an affordable package.

Technical Data

Frequency response
<10 Hz - 400 kHz (-3.0 dB) THD+N
@ 0 dBu, 20 Hz – 22 kHz: 0.0018 %
@ +10 dBu, 20 Hz – 22 kHz: 0.005 %

Noise floor
20 Hz – 20 kHz (A-weighted): -98 dBu

Dynamic range
20 Hz – 22 kHz: 120 dB

Maximum level
Input: +21 dBu
Output: +21 dBu

Impedance
Input: 10 kOhm
Output: 68 Ohm

Power Consumption
70 Watts

Sounds Sweet

“The xfilter sounds sweet (with a Class-A quality), transparent (with no artifacts) and quite versatile for an ‘only 4 band’ equalizer. Crosstalk channel to channel measures EXCELLENT. I’m sure that degree of stereo separation across the audible spectrum enhances its performance.

It also seems to enhance the stereo space, so the distortion is ‘just right’. The versatility of combining the low cut with bass boost or cut or the high cut with high frequency boost or cut is amazing. You can get any shape out of that from gentle to very steep. Well done! I’m very happy.”

Bob Katz | Mastering Engineer | Longwood

Love it!

“What a fantastic piece of equipment the xfilter is – I absolutely love it!”

Stephen Marsh | Marsh Mastering | Los Angeles

“30th Annual Technical Excellence and Creativity Awards – elysia xfilter nominated for outstanding technical achievement in the category of signal processing hardware.”

NAMM Foundation | TEC Awards 2014