How To question - keyboard sound - arpeggiated and/or LFO movement - how is it done?

It's normally best to provide a link to the song rather than assuming that everyone is familiar with it. Anyway I found one that's backing track only:
http://www.youtube.com/watch?v=S3BiFaMLGWI

Seems like a good candidate for using several instances of Rapture and messing with its LFOs and step sequencers.

Well, it's a synth patch with is carefully messed with throughout the song (simple filter eq - strong lowpass early on which opens up more high end as the chorus builds). I'm guessing it's a tremolo on the patch with a square shaped response pattern (rather than sinusoidal). Well, most likely a blend between the two, but slightly more squarish in shape I think. It 'could' be a delay that is triggered internally in the synth and cuts when the keys are released, but I think it sounds more like a tremolo.

Hmm, on a second listen, the attack seems to be on each 'pulse' which suggests it might actually be a delay. Really not sure.

As for actually creating the patch, I don't know much about making synth sounds, but it does sound pretty standard and simple just tuned well for the song. I guess it's made up of a few layers though. It could be more complex than it initially sounds. In fact, a second brighter patch definitely comes in later in the song playing the same notes. I won't go into more detail because I can't. Jeff Evans tends to be pretty good with this stuff. I'd suggest you shoot him a PM if he doesn't chime in. I'm sure he can dissect it well.

It is not difficult with the right synth. Hit once, repeat in eighth notes the rest, and real-time control movement for the rest. An arpeggiator will do that and a synth that has real-time controls that can be moved while only one hand is doing the chord in the song.
 
Nothing to it with a little bit of practice.
I think my synth - Juno Stage could do it. Set the tempo of the patch to the tempo of the song and set the arpeggiator for the rest of the measure and move controls that alter whatever is altered back and forth.
 
 

 
Back when Jerry Lee Lewis did it they just called it 16th notes.

We can all agree that there are many ways to achieve the same result here.  I like to use combinations of the techniques mentioned when more emphasis is needed.  For example, sawtooth LFOs sync'ed to a step sequencer for added attack, 'doubled up' parameters in a Mod Matrix for depth, or one-shot LFOs as an additional envelope with an arpeggiator. 

Since the OP mentioned Rapture, there's another useful technique to explore in the Step Generator now:  Retrigger Steps.  As a start, bring the odd-numbered steps up, the even-numbered steps down, and alt-click on each of the odd-numbered steps (those steps are now highlighted). 

Whatever is in the Envelope Generator will be retriggered on the alt-steps. Works best with an AD envelope without a sustain point (press S over the node with the vertical red-orange line).  Or create your own with two node-clicks in the EG.  By gradually reducing the step heights over the length of the sequence, you can superimpose an envelope shape over the entire phrase.

 
I think most of the "movement" I hear is based on the interaction within the arrangement rather than an effect on the keyboard.
 
I'll defer to Brock regarding how one might do it with the tools he suggests.
 
I'd take an "electric piano" sample, maybe pull back the attack with the ADSR, maybe add some modulation using some sort of tool. (I might just flange the whole thing real slowly). I make a point of making sure the velocity of each note created the sense of undulation that we here... just like a pianist would.
 
Like I say, I think the real sense of movement is from the way the other instruments layer up over that basic 16th note ride.
 
I'd enjoy seeing a patch of what Brock has in mind... it would be fun to learn about it.
 
best regards,
mike
 

b rock -all I can say is wow! Thanks!

I haven't tried this yet, and I'm not entirely sure I can follow your well described recipe for this approach, but I'm going to try!

I presume I'll have questions as I walk through trying to follow what you've noted, but this is very helpful indeed.

Really appreciate that you put this thought into the details.

It's a cool sound they pulled off so I hope you enjoyed the experiment for yourself as well.

Thanks b rock.

1).  With a patch from scratch, two important design decisions are the starting waveform and filter choices.  In theory, the Cutoff frequency is where the filter chops off the waveform.  The reality is that it slopes off at a given rate.  A Low Pass 4-pole (24dB/octave) slope is one very common filter type (Moog).  So is a LP-2 filter (12 dB/Octave - Oberheim).  I initially thought that the muted example sound would work best with a more gradual slope.  It turns out that the Cut 1 LFO modulation and Mod Matrix reacted better with a steeper filter slope.
 
2).  I tend to do my synth programming in a standalone or micro-host.  Free from context, outside influences, and potential problems.  The presets always get tested, tweaked, & utilized in a DAW, but don't start out that way.  Tempo / BPM will give the same results no matter what.  But a preset like this is based heavily on sync-to-tempo.
 
In Rapture, there's an Options button (2nd icon of 4 to the left of the RAPTURE logo).  In there, you can defeat the lock to outside MIDI Clock tempo, and use an internal generated tempo.  In most cases, you wouldn't want to use this.  But in a standalone situation, it comes in handy.
 
If it sounds right to you, then you're where you want to be.  When I used StepGen Retriggers, the AMP envelope triggers were set up on every other step.  The steps following each retrigger tended to sound like 'rests'.  So I doubled the tempo for programming (description) simplicity.  In hindsight, I should've just stuck with 80 BPM, the same AMP Step Generator description, change SYNC setting and number of steps, etc.  Whatever it took, as opposed to 'the easiest way'.
 
3).  The first method for the AMG EG was the correct one.  That was a bad analogy on my part.  You want to go top-left (near-instant attack) to bottom-right (silence).  The Sync parameter uses the entire default AMP EG display as its Sync 'increment' (1/2 of a quarter note 'beat' = 1/8 note).
 
As for the "two (additional) nodes)" ...  When you first open up Rapture, you'll see a default node in the bottom-left of every EG display.  It can be moved in level (up & down), but not time (left-to-right).  It comes in handy when you don't (or you do) want an instant high-level start to your envelope.  Your MIDI Note instantly triggers the envelope.  In many cases, an instant level change like that can lead to a "pop" (psychoacoustic, or otherwise).  All it takes is about a fractional millisecond delay to avoid that.
 
"Two (additional) nodes" meant to not count that default node as one of them.  It's easier to just right-click in two spots, create your envelope, and have that default node there for later on.  If you find yourself with a pesky little popping sound (often the culprit is an AMP EG or CUT1 / CUT2 filter EG), all you have to do is nudge your first right-clicked node slightly to the right.
 
4).  Sync vs. Freq.  If you dial any Sync parameter beyond 1/8T or 128, the Sync control goes to OFF, and the Freq control becomes active.  [The fastest way is to left-click + right-click on the Sync parameter.]  You're no longer synchronized to tempo.  The speed/rate is now frequency in Hertz. (cycles per second).  When you hit a MIDI Note, the cycle starts.  If you look at a default LFO display, you're seeing two LFO cycles displayed (somewhat counterintuitively).
 
The only point that I was making there is there is an equivalent rate in Frequency / Hz. to whatever BPM / Sync rate you're using.  [Google BPM to Frequency Calculator or charts.].  Sometimes, you want the MIDI Clock tempo to keep your synchronization timing for you.  Other times, you'll want to have your chords trigger the start of a sequence, envelope or LFO cycle, and have the speed of the events determined by a predictable rate.
 
5).  The Cut1 LFO modulates the Cutoff frequency of Filter 1.  (The same scenario and layout goes for Filter 2.)  In this example, you set an initial frequency point for the LP4 filter to drop off using the left-most CUTOFF knob.  I had you center the control at about a 12 0'clock position.  Mine happened to be set to 500.8 Hz., but it just had to be close to that.
 
The Cut1 Low Frequency Oscillator starts at this initial frequency [500.8 Hz.], and brings it above and below it.  The Sync or Freq determines the speed that it modulates.  The Depth determines how far up & down it deviates from that initial frequency.  Look at the Sine shape in the graph.  It starts at the midpoint [initial Cutoff knob position], goes above it, down through midpoint again, below it, then back to the initial Cutoff knob position.  [Twice over, because 2 complete cycles are represented in the graph.]
 
I had you set the Depth control there to 1200 cents (one octave).  But the LFO is a bipolar modulator (above and below the initial Cutoff position).  I steered you wrong with 600 cents up and 600 cents down.  Apparently, I was calculatiing that the Depth was halved for each of the directions.  But that just sounds like a brain-fart that slipped through from the "speed programming" exercise.
 
I just tested a similar scenario using Pitch and Pan LFOs,  Full Depth Up, and Full Depth down.  So the effective Depth total excusion [up + down] is doubled, not halved.  You can test it yourself:
 
Pitch LFO
Display: Pulse/Square 3
Status: On
Depth: 100
The rest at defaults.
 
Play any MIDI Note.  It sounds like a WWII Euro ambulance (without the Doppler effect).  One semitone [100 cents] up, and one semitone [100 cents] down.  Now, turn the Status to Off.  You have the original played note smack in the middle.

Check this out, forward to about 6 mins and 10 seconds in to the video. And Viola... The boys at fab make cool stuff. You can watch the whole vid too, but the part you're interested in is right there at 6:10. It does "exactly" what you want... And since you can trigger it using a percussive track, you can get a nice smooth live feel by playing the midi part in, and if you choose you can quantize, use different beats in different parts, etc...
 
http://www.youtube.com/watch?v=X6IpvmqZLR8

Yeah, different ways to skin the cat. Many ways to get the hair off that thing? What we're all interested in at the end is a hairless... 
 
 
"cat"

Yeah, too bad no one mentioned a gate? 

Reviving a previous question with a new angle.  To recap, brock helped illustrate how to get this particular sound / vibe out of Rapture, which is really cool.
 
The new question I have, if anyone can reply, is what kind of approach / settings might be used to approximate the sound using Omnisphere?  I'm sure it can be done.  Just trying to figure out how.