Arranger keyboards are characterized by their automatic accompaniment styles, which are essentially multi-part MIDI riffs that follow your chord changes, adding not just a drum beat but several virtual musicians worth of backing band as well. Their feature sets and price points range from basic accompaniment and easy-play features found on some $149 Costco impulse purchase to the $6,000-plus Yamaha Genos shown above, a songwriting and performance monster machine that can basically sound like anything and do anything. Arrangers are also some of the most maligned and least understood keyboards among many pros.
Blame it on the Bossa Nova button. Arrangers' reputation for "cheese factor" is a direct outgrowth of the home console and spinet organs of the 1970s through the early '80s. Walk through a mall during that era, and you would likely come upon a dais occupied by an organ replete with "one man band" features that may be rudimentary by today's standards but that never failed to amaze in the hands of the inevitable mulletted demo wizard. You too could play along with the equivalent of the CBS Orchestra -- or maybe at least Lawrence Welk's outfit -- in your living room! Heck, Australian songwriter and inveterate synth geek Gotye wrote a love letter to the whole concept. (Yes, the Lowrey Cotillion is an actual thing and he actually used a ton of its sounds in the tune.) Even when a sci-fi drama with as much gravitas as Orphan Black wants to throw in a little kitsch and comic relief, it brings out the arranger keyboard -- in that case a Korg Pa-600 played by "sestra" clone Allison.
Despite their admitted use entertaining the sorts of people that return conspicuously often to the shrimp cocktail at the cruise ship buffet, a good-quality arranger sounds fantastic and is an incredible music-making tool in the right hands. But I'm going out on an even longer limb:
Properly understood, arranger keyboards have more in common with Ableton Live than with just about anything else.
Specifically I'm thinking of Ableton Live's Session View, where audio and MIDI clips can be, ahem, arranged, triggered, processed, and repurposed in real time. Session View is so open-ended that there are almost as many ways to use it as there are skilled Live producers, but a common application is that during a dance set, how the performer must "work the room" is full of variables. A song section that was only supposed to last a few bars might really be doing the trick and therefore need to be repeated indefinitely as it's varied. Those who perform live with Live often use channels in the Session View to stack up different intros, fills, main song variations, outros, and other arrangement building blocks.
The performer playing live on an arranger keyboard is often in a similar situation, for which the instrument provides similar tools. If playing solo, using backing tracks of fixed length gives you no options when the crowd really does (or doesn't) want three more rousing choruses of "Sweet Caroline." Hence, arrangers have not just styles, but style sections triggered by buttons.
Not unlike Session View, these typically involve a number of different arrangement blocks: intros, main sections, endings, fill-ins, etc., that you can switch between to build a song or perform live. Song sections usually go from simple to "busy" as you progress through the options. On many arrangers from mid-market up, you can also edit your own variations on the factory presets for all this stuff, and edit the sounds they play in synth-like ways, plus add audio effects. Provided the machine has great sounds, if you don't find a factory style with enough cred for your take on dubstep or death metal, you can create one.
Now start to imagine each of those sections as a channel in Session View, and each of those buttons as a clip launcher, and the parallel becomes obvious. Of course you can do more at one time in Ableton, as it's software and therefore open-ended. On the other hands, because an arranger's styles and subsections are all really just MIDI loops driving the keyboard's internal sounds (though some arrangers offer audio-file-based styles as well), they're more manipulable than audio loops in many respects.
So that's my manifesto on why arrangers are a lot hipper than you might think. They essentially give you a needle-drop riff library that you can (usually) customize even further, and let you throw these "molecular" chunks of music around in real time, intensifying or utterly changing the mood of a performance as the crowd demands.
This is just one aspect of arrangers but for my money, it's the defining one. Next time I talk about them, we'll tackle the subject of articulations on instrument sounds -- another thing arrangers are very deft at doing in real time.