Future Music 03/2014
Robbie Stamp: "The xfilter 500 will behave like a smooth professional and you can trust it to enhance without degrading, and yet it offers a world of radical reshaping that makes it a highly creative tool. I’m having a problem thinking of a reason not to buy one."
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Music Tech 02/2014
Mike Hillier: "The xfilter is a fantastic and versatile tool that we would happily give a place to on our stereo mix buss. However, it isn’t limited to this role and performed fantastically on just every sound we put through it. At this price, the xfilter is almost a must have tool for your mix buss."
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Audio Xpress 12/2013
Miguel Marques: "While testing the xfilter 500, I felt elysia created one of the finest equalizers I’ve ever heard. All in all, this is definitely the type of gear that serious professionals will want to have as it will pay for itself, due to its excellent sound quality, adaptability, and build quality."
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Tape Op 11/2013
Eli Crews: "The xfilter 500 has done what I've asked of it on every occasion - make what I run through it sound better. Whether I'm looking for sheen, warmth, bottom, midrange, sparkle... the xfilter has performed dutifully and happily. The Passive Massage really is a treat."
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Mix Magazine 11/2013
Brandon T. Hickey: "There is certainly a need for this new tool, and with the ability to find the best in any piece of audio and exploit it, it’s hard to imagine any future competition outdoing what elysia has already done here. A whole rack of these would be a welcome addition to any studio."
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Tools4Music 10/2013 
Christian Boche: "After all, there really is something like 3D in audio – the three 500 series modules by elysia build a triptych of great sound, in which the xfilter plays the role of a delightful indulgence. All in all, this is audio culture at celebrity chef level.“
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Bonedo 07/2013
Hannes Bieger: "Trying to explain the sonic spectrum of the xfilter 500 would go like this: Clear, open, punchy, but still with pretty silky air... The elysia EQ proves at once what an explicitly powerful tool it really is. Looking at the very high grade hardware and the vast potential of it, the price is absolutely OK."
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Audio Times 06/2013
Robert Campbell: "First thing to say is that the elysia xfilter 500 is a very classy sounding equalizer. If you need a really high quality stereo EQ for stem and 2-buss work then you should audition the  xfilter 500. And of course it will work its magic across a whole range of mono and stereo sources as well."
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Professional Audio 06/2013
Georg Berger: "Once more elysia shows that a great sound, striking features and transparency do allow a favorable buying price after all. The manufacturer remains true to its principles, which could be summed up as high end sound and quality at a low cost price, or 'Class-A for the people'."
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Pro Tools Expert 06/2013
James Ivey: "I'll be very reluctant to give this one back, I have to admit. The pots feel nice, got a real quality feel about it. As a mastering EQ or as a buss EQ, it's really really powerful, very clean and really nice. Thanks so much elysia for that one!"
> Watch the video...

elysia xfilter 500

by pan60

pan60: So guys, let's chat about EQs. What a broad subject... It seems to me it is a broader topic then let's say preamps or even compressors.

elysia: This is really a very wide field indeed. It's hard to find a start, as there are so many aspects to cover:

- Topologies (analog, digital, active, passive...)
- Purposes (corrections, enhancements, placements of signals...)
- Situations (recording, mixing, mastering, playback, acoustics...)

But what we can say for sure is that an EQ is one of the most universal tools we have in music production. It helps in solving problems or being creative, or ideally both at the same time.

It also helps us to understand that almost all of the music we hear is artificial in the best meaning of the word, as the vast majority of signals is being EQ'd before being published instead of being all 'natural'. This starts even earlier with the frequency response of mics, pickups, and so on, but that is something for a different article, I guess.

The bottom line is that we want to and often need to change the way a signal is perceived or how much space it takes in the frequency spectrum, and bending its response is a very powerful way of achieving this.

pan60: Can we talk about the different types of EQs first off? I mean, there is this basic separation between active and passive EQs, so what's the deal with this?

elysia: This separation refers to the actual filter section of a specific EQ. With very few exceptions, so called passive EQs include active amplifier stages (tube or transistor based) as well, for compensating the loss in gain which their filter network causes.

However, the actual filters in such an EQ use certain combinations of inductors, capacitors and resistors only for changing the frequency response, and these are of course all passive components.

And as such networks often need just a single amplifier stage for making up the lost gain, they are considered to sound very puristic. Some of them are also popular for their somewhat special frequency curves, like the historic Pultec design.

Active EQs joined the game a little bit later with the availability of components needed for coming up with more complex circuitry. Even though it is not always the case, they tend to be more flexible than their passive counterparts.

The next question would be: Which one is better, right? The answer is the same as with “Tube or Solid State?” – it depends. And it depends on a lot of things, like your individual taste, the material you want to use the EQ on, what you want to achieve with it, and especially the specific product you are planning to use.

I have listened to some very good passive EQs working sheer magic, while others were rather mediocre. And exactly the same is true for the many active EQs I have experience with. In my opinion, it's better not to make a religion out of this...

pan60: What about the Q factor? Wide or narrow, fixed or adjustable, constant or proportional – what can you tell us about this magic letter?

elysia: Well, first of all the Q factor tells us how wide or narrow the peak of a bell filter is – a high Q value stands for a narrow peak, while lower values determine broader curves. Once this parameter becomes selectable, we have an influence on the range of frequencies around the chosen center frequency.

In practical use, it often turns out that we like to boost with wider curves as it is pleasant to the ear, while cutting often needs more precision and therefore higher Qs. But the actual implementation of this into an EQ really depends on what will be its main application.

For example, some bass preamps follow the above and always boost with a low Q and cut with a high Q without giving the user any access, and it works just fine. The mastering guys, on the other hand, often depend on having the choice of Q as flexible as possible and therefore selectable through wide ranges.

These are just two examples, but they already show that there is no perfect way of implementing the choice of Q in a way which ideally meets the demands of all possible users at the same time.

Sometimes you want to work fast and don't want to interrupt the creative process by fiddling around with your knobs, sometimes you want to address certain problematic frequencies and then you really depend on precision and flexibility/complexity.

The question if you have a constant Q (the 'broadness' of the curve remains the same, no matter how much you boost or cut) or a proportional Q (the curve becomes more narrow the more you boost or cut) basically results from the topology of the filters.

But apart from all technological details, the most important requirement is that all individual filter curves also work in perfect tune with all other filters in a specific EQ at the same time, which requires quite some fine-tuning.

We like the two selectable Q factors (0.5 and 1.0) on our EQs, as they are very musical and useful in lots of different situations. This way, the mid bands work fast and efficiently, but you still have the option to tweak their response according to your material. 

pan60: Please explain phase issues when it comes to EQs, and how these can influence a signal. Is this a problem we have to life with, or can it be avoided or corrected?

elysia: Oh boy, this could fill a book! But for a start, almost all analog filters change the phase of a signal. But that's also true of speaker chassis, pop filters for microphones and so on... so I'd call it a natural phenomenon. 

Coming back to our subject of EQs, the question of how strong the phase is influenced depends on the topology and parameters of the specific filter. On a side note, there is also a type of filter that only changes phase without influencing the frequency response: The all-pass filter.

The human ear does not detect much of a difference when a signal is being processed with an all-pass, and this is because the spectrum of harmonics is analyzed instead of phase relations between the individual harmonics.

Phase starts to play an important role especially when two individual signals are mixed. Just take the snare drum as an example, which is often recorded with one mic on the top and one on the bottom – if phase is not set correctly in this case, very audible cancelations will be the result. And a coherent phase is also important when processing stereo signals.

With some exceptions in the digital domain, most EQs are not really linear when it comes to phase... but we should not worry about this too much: A lot of great sounding recordings have been made with them ;-)

pan60: OK, let's become a little bit more specific now and have a look at the xfilter 500. One thing which directly jumped at me is the “Passive Massage”... Please tell us why and how this section has been integrated, and how it interacts with the active filters?

elysia: Many users of passive EQs love their machines especially for this unique, magical shine they ad to the high frequency range. It's a very smooth, natural, big and yet unobtrusive kind of top end which we wanted to implement into the xfilter by all means, and hence the Passive Massage was born.

As we wanted to have this as an additional option on top of the existing active filters, we decided for a switchable fixed LC filter which mainly consists of a capacitor and a coil per channel. But unlike the standard shelving designs, it has a slight resonance peak at 12kHz and starts to fall of at 17kHz.

This is certainly not the 'usual' design, but when you hear the results, you will instantly notice why it makes a lot of sense: With this special frequency response curve, the saturation-like storage effect of the coil focuses on the area around the peak without pushing the complete high frequency spectrum too much.

There is no interaction with the active stages at all, which is good because the results are always predictable. Also, the Passive Massage has been designed in a way that does not require any additional amplifier stages, so this filter is as pure as it gets.

pan60: And you have more interesting things going on with your filters, right? I am talking about the fact that the shelving filters can be switched into high and low cut filters with an additional resonance peak. What is this all about, and when could it be useful?

elysia: In our book, this is one of the greatest features on an EQ ever. The first time we implemented this was when we released our flagship equalizer, the museq. People absolutely love it, as it provides quite unusual filter curves which would take at least two bands of a standard EQ to reproduce them.

From the technical angle, the resonance filters are high and low cut filters with 12 dB per octave and an additional resonance peak at the knee frequency, which can be changed in its intensity. But what are the actual benefits?

One really striking example is bass frequencies that 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.

But also in the high frequency range, you can use a 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.

It's one of these things you never want to miss again once you have them around...

pan60: Alright, that's already two remarkable specials on this machine. Is there anything else we have not talked about yet? I mean, any further interesting features or functions?

elysia: What I consider worth mentioning is the great amount of effort we have put into making this equalizer a linked stereo one at a very reasonable price. You know, there are almost no linked stereo EQs in the market at all, mainly because of the problems that components tolerances inflict with linked filters.

We took some quite crazy measures to get around this... for example, every single of the all stepped potentiometers in the xfilter is measured and selected with a custom microprocessor-based tool and software 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 will never see the inside of an EQ.

In addition, we use a special series of film caps which sound amazing and come with a  maximum tolerance of 5% only. This is twice as good compared to the components you will find in most of the EQs out there.

All these efforts aim at a single, very important goal: A truly accurate stereo image. Sounds like the typical custom shop options? Correct, but with the xfilter we have implemented these in serial production and without any up-charges.

pan60: After all these interesting details, I think I have one final question for you. From my reviews of the xpressor 500 and the nvelope 500, I know that your processors are usually on the clean and transparent side of things. So, how does the xfilter 500 sound?

elysia: It's certainly no secret any more that we absolutely love class-A designs, and the xfilter is no exception. It breezes everything we expect from this type of audio topology: A transparent, wide and open sound that does not degrade the quality of the original signal.

I would say that the xfilter can be very punchy, too, because it passes transients 1:1 and also comes with a nice secret weapon for creating really powerful sounds: The resonance filters! At the same time, the Passive Massage ads a more airy, less tight, generally very pleasant flavor to the complete picture.

So, in terms of sound, the xfilter stands in the same line with all the other elysia products, and just like its brothers and sisters, it comes with a remarkably flexible feature set which allows the users to put their individual ideas into place.

pan60: A very nice piece of gear, as expected. elysia delivers, yet again, in a very cool 500  form product. The basis for more gear lust! The xfilter 500 would be a welcome addition to anyone’s gear collection. I have had it on a two buss mix for some time, now, running a  number of mixes through - and I am loving the results! A big thumbs up guys! If you are looking for a two buss EQ, don’t hesitate to check the xfilter 500 out :)