1989 Kawai K4 - Digital Resonant Filter (DCF) Demo

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I recently bought this vintage Kawai K4 imported from the USA because I'd heard good things about it. I was most intrigued though by the fact that it's a polyphonic synth with digital low-pass resonant filters (as in written purely in code rather than code controlling analog filtering) which makes it one of the first on the market to offer this alongside the Yamaha SY77 and Emu EMAX II which I've been informed all launched in 1989. The Roland D50 had something that sounded very filter like with it's 'TVF' back in 1987, but this was only available on square and saw waves and was more of a mimic of a filter. So I'm told anyway, I never used any of the other gear I just mentioned 😄

So considering that it was this early in the game I was very interested to hear what it sounded like but couldn't find any other filter demos on YouTube, so here's mine. I was planning something more involved showing how to edit a patch etc, but I got carried away playing and ran out of time. Maybe in another video.

All the examples shown use the brightest saw I could find (the waveforms are sampled) in a single slot with a single filter. I played around with the 'auto bend' which is a pitch sweep envelope, slowing it right down but making it velocity sensitive to give a kind of fake analog drift to the sound. If setup correctly a single patch can have 2 filters either in parallel or serial modes but I haven't experimented with that yet. I also used a bit of it's built in delay and chorus effect.

Actually the K4 has decently sophisticated spec and routing, especially for 1989. Up to 4 waveforms with their own volume envelopes and 2 filters can be used, amplitude modulation can be set up between waveforms, there are separate vibrato and filter LFOs and some decent features for expression like routing velocity to the filter cutoff or filter envelope amount, mod wheel to filter, aftertouch etc.

Anyway I really like the sound of this filter. It's pretty convincing to my ear, only occasionally giving itself away as digital with a kind of uncanny feeling that appears a couple of times in this video. It's not a ladder like filter design, turning up the resonance will not reduce the gain or loose the bottom end, it just adds gain at the cutoff resulting in me having to adjust volume throughout which you may notice. In fact it can even be 'pinged' or at least something that sounds like that, very short amp attacks for example produce and plucked sound which has me confused for a while when building a patch from scratch. Softening attacks and releases is essential if you want to tame it. Zipper noise can be occasionally heard too which is down to the fact there are only 127 possible positions for the filter so moving the cutoff sometimes sound like crackling. There are only 7 levels of resonance too.

Editing isn't the easiest it has to be said but at least it i fairly well organised. Each source can be selected and muted with dedicated buttons then sections for dco, filter etc can be cycled through and edited with a single slider. It works but it's slow. Luckily there is a very good free editor called Edisyn that supports it: https://github.com/eclab/edisyn

I also have a Kawai MM16 which can apparently be used as an editor for the K4 but I haven't had time to try that yet.


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