There's been a lot of discussion on the forums about "phat" filters. Fueled by a lot of posts from a certain you-know-who whose forum name begins with an "f".

I'm here to set the record straight. There is no such thing as a "phat" filter.

Filters aren't "phat". In other words, they don't impart anything to a sound, they are what sound is passed THROUGH. When people say a filter is "phat" what they are really referring to, whether they know it or not, is the sound of the oscillators, and the sound of the D-to-A converters. Much like water flows through a coffee filter, sound passes through a synthesizer filter. It's the same principle.

Now, I should clarify something. Can a filter make a sound on its own? No. But, a "low-pass" filter (the type found on the original analog synths) can be set up in a way so that it will "self-oscillate" - that is, the cutoff and resonance and emphasis can be set so that the filter itself begins to "whistle". At this point the filter's sound takes over and becomes its own oscillator. With very careful programming, the filter in self-oscillation mode can be set up to track up and down a keyboard, producing something that sounds like a pitched scale. This was one of the coolest things about the original Moog low-pass analog filters - they could be driven into self-oscillation quite easily. And the self-oscillating moog filter sounds quite good. When people talk about the quality of a filter sound, they are holding it up against the analog Moog low-pass filter, which is still considered the holy grail of filters.

Low-pass digital filters will self-oscillate, to a degree. Most, though, will not produce a pleasant sound. It will be scratchy and shrill and harsh and reedy. The degree of unpleasantness will be directly related to how good the digital filter is. In the case of really poor digital filters, with the cutoff set as low as possible and the resonance and emphasis set as high as possible, you will hear just a bit of the filter whistling, along with the scratchy, reedy, shrill tone I described. An example of a poor digital filter is the one on the softsynth called Vanguard. The filters in Cakewalk's Rapture softsynth also suffer in this way.

The filters on the Motif ES are very good digital filters. You can indeed get the low-pass filters to self-oscillate (the 24D, 24A, 18, and 12db filters are all low-pass filters). And the tone, while not as good as that of a true analog filter, is better than the filters on any competing products. You can test this for yourself - let's say you have a Korg Triton. Set up a new voice with just one oscillator, like a sawtooth wave. Set the cutoff of the filter as low as you can set it, set the filter resonance as high as you can set it, and set the filter emphasis high. You will hear almost no self-oscillation. The results of this test are better on the Roland FantomX, but still not as good as the Motif ES filters.

The filters in the Motif XS go beyond what the ES has to offer - they sound even better.
This is due, in no small part, to the new chip in the XS and the improved D-A converters. I've said it before, and I'll say it again - the filters on the Motif XS are by far the best sounding digital filters I have ever heard.

I should add that different filter "types" produce different results. While I won't go into a long-winded tutorial here about filter types, let me just say that high-pass (HPF), bandpass (BPF), and band-eliminate (BEF) filters produce different results than a low-pass (LPF) filter. Particularly with high-pass (HPF) filters - the result is incredibly thin-sounding unless the cutoff frequency is set close to zero. That's what a high-pass filter does - it filters OUT all the lower frequencies, so you end up with a thin "sliver" of sound. How anyone could ever think of a high-pass filter as being "phat" is beyond me. That's another discussion for later...suffice it to say, the Motif family of synths have 18 different filter types to choose from, and that's a heckuva lot of filtering options.

But let's not forget one last thing. What is the only thing you actually hear when you play a synth? It's your speakers. Speakers are the only components that actually produce a sound (yes, headphones are still speakers). How "phat" your synth sounds is directly impacted by the quality of your playback system. Don't judge a synth's sound on what is coming out of a cheap hi-fi system, or computer speakers, or through a set of i-Pod earbuds. I can't tell you how many times I've heard comments like "that doesn't sound very good", and lo and behold, the person is listening through a cheap guitar amp or a set of multimedia computer speakers. Another comment - "I heard it at Gutar Center and I wasn't impressed". Guitar Center is no place to truly audition a synthesizer - there's too much noise going on in that environment. Get yourself a listening situation that includes a room with some sound baffling and non-reflective surfaces, and the best quality monitor speaker system you can get. Then you will be able to truly appreciate how good, or bad, a synth sounds. Or should I say, how "phat" it sounds.