Review – Strum Electric and Strum Acoustic from Applied Acoustic Systems

The wizards at Applied Acoustic Systems have a way with math. We look at how mathematical simulations can conjure up an impressive pair of guitar instruments.

by David Baer, Mar. 2014

A PhD in physics and a PhD in mathematics walked into a bar.  Well, OK, maybe it wasn’t a bar, but in 1998 the two PhDs, both also musicians, got together to found a company to produce music creation computer software.  And if that amount of mental fire-power weren’t enough, a third PhD joined the team later that year.  So it should be no surprise that Applied Acoustics Systems (AAS) turned out to be other than your typical soft synth development operation.

What AAS specializes in is acoustic modeling – generating sounds that have the same characteristics as the real-world behavior from formulas.  From that as a starting point, one can also generate sounds that have no equivalent in reality by altering some of the parameters used in the sound generation.  AAS’s Chromaphone, which combines various models to produce the sound of drums, mallet-played instruments, and more appeared in 2011 to high acclaim.  Although I’ve had no experience with Chromaphone, AAS’s Ultra Analog, a decade-old virtual subtractive synth, has long been a personal favorite.

I had somehow completely overlooked AAS’s two guitar modeling instruments, Strum Acoustic and Strum Electric, introduced in 2008 and 2009 respectively.  But when Cakewalk bundled the former with its latest release of SONAR, Strum caught my eye and I though a closer look would be in order in spite of them being a half-decade old.  So that’s exactly what we’ll do right here.

Read the Fine Manual!

It’s convenient to discuss both of these instruments by separating the keyboard-to-note translation function from the function that produces the sound.  So from here on I’ll cleverly refer to those aspects as the front end and the back end .  While the back ends for both Acoustic and Electric have much to admire, to my mind the most innovative thinking went into the front end, which is essentially identical in Acoustic and Electric.

It’s clear from the get-go that AAS’s intent was to provide a piece of software that allows a keyboard player, even one who has never even held a guitar, to realistically produce music that sounds like it is being played by an accomplished guitarist.  What they devised to achieve this basically discards all conventions for how a software instrument uses keyboard MIDI input.

And because this is so, it is more vital to read the manual than any other instrument I’ve encountered.  Approximately one-third of the superb documentation is devoted to explaining this.  One might be able to understand all this by trial and error, but trust me – it will be far faster just to RTFM.

AAS almost certainly had a guitar player on staff or brought one in as a consultant when designing Acoustic.  While there are endless varieties of music that could be played on a keyboard but not a guitar, it’s all but impossible to play something through Strum that could not truly be played on a guitar.  I’ll attempt to explain briefly, but there’s far too much detail to adequately cover everything in a review.  With Strum, the documentation will be your friend.

Here’s the basic concept.  Just like a guitarist, the keyboardist uses the left hand to control the notes in a chord (i.e., how the fingers would be positioned on the guitar neck) and uses the right hand to pick the strings.  A range of keyboard notes is dedicated to the neck hand and another range to the picking hand.  Below is a diagram from the documentation (it’s the same diagram in the Acoustic and Electric manuals) that will help explain.


MIDI notes 40 thru 70 are “neck hand keys” or “note keys”, if you prefer.  MIDI notes 71 thru 84 are “picking hand” keys.  An option is provided to add an additional octave of note keys.  I’ll explain the picking hand keys in more detail shortly, but let’s first concentrate on the note keys.

There are two modes in which to play: Auto-strum enabled causes notes to sound when the note keys are played (we’ll get to Auto-strum disabled in a moment).  However, they do not have a normal keyboard response.  Play one keyboard note, the note sounds – nothing unusual so far.  But play a note, and while keeping the first note depressed, play a second.  You’ll hear the second note sound.  Now add a third note and you’ll hear a chord in which all three notes sound.  Strum really, really needs to … well, strum!

Want to play that pretty little Bach prelude on your keyboard that you took so much trouble to learn but have it sound as if played by guitar?  Strum is not the right tool for the job.  Yes, you could probably work out how to do it, but it would likely be a tedious and frustrating process.  Strum wants to keep you authentic as a guitarist and there’s not a lot to be gained by fighting that tendency.

The note mapping function translates three or more notes into a chord (usually successfully unless you’re doing something far off the beaten harmonic track), and then translates that information into a configuration of notes that a guitarist would be able to play.

And that brings us to the picking keys.  As can be seen in the diagram above, C5 is labeled Downstroke and D5 Upstroke.  When you have a chord selected by playing some note keys, pressing C5 produces a strum in which multiple strings (low to high) are picked in quick succession – which is a lot of words to simply say a strum happens.  With D5, the sequence is high to low.

There are several variations on the strum.  One is the palm-muted strum – a term guitarists will know but which the documentation fully explains for non-guitarists.  And there’s the alternate strum, using different (fewer) strings in the strummed chord.  White keys in the range E5 thru C6 can be used to play individual notes in arpeggios.  But they don’t translate directly to the six strings on the guitar.  The low note will be determined by the note-translation function.  One or more of the high arpeggio notes may repeat the same highest string note.

Now, finally, we return to Auto-strum.  As explained above, when Auto-strum is enabled you get sounds as you play note keys and you also get sounds as a result of using the picking keys.  But when Auto-strum is disabled, playing note keys produces no sound.  That only happens when playing picking keys.  I have a feeling that a lot of first-time Strum users will have the same initial reaction that I did.  At first, you feel the need to have Auto-strum on – you play keyboard notes, you expect to hear sounds.  But I also expect that many Strum veteran users will prefer to have it disabled.  Enabled or not, the picking keys are always active, and they do a much better job than your left hand fingers in producing a guitar-like sound.  That’s my guess anyway … your mileage may vary.

Next, let’s consider the on-board sequencer.  Guitar stylings can involve complex repetitive patterns.  When using Strum within a DAW, this is no big deal.  But playing live is another matter.  Guitar patterns can be complicated and requires good keyboard technique.  With the MIDI loop player, this challenge can be circumvented.  Strum comes with a good selection of pre-programmed patterns.  Even for those not wishing to use these in performance, they offer an excellent reference or starting point for developing one’s own stylings.  In Acoustic, there are sibling patterns, one of which contain both chords and “picking notes” in the sequence and one without the chords.  The former is useful as a learning tool to get an idea of how the pattern might be applied to your own music.  In Electric, the patterns all are fully fleshed out demos.

There is much more detail – too much to mention here.  For those curious to learn the full story, the manual for either instrument can be downloaded from the AAS web site.  You don’t need to install a demo version just to get your hands on the documentation.

The Might of Mathematics

Time to turn our attention to the sound production technology.  If the front end is inspired in design, the algorithms used to implement that design are probably relatively straightforward.  The back end is likely the opposite.  The design appears to be rather conventional, but it’s fair to assume that the mathematics required to implement sound production are scarily complex.

Let’s take one aspect as an example of something that’s common to both Acoustic and Electric: modeling the plucking device, which can be a flexible object (e.g. a thin plastic pick), a non-flexible object (e.g. a metal pick) or a finger.  The following illustrations from the documentation illustrate the parameters involved in setting up this aspect of the model.

Add to this the need to incorporate string characteristics, bridge characteristics, body characteristics (Acoustic) and pickup characteristics (Electric) and you might begin to appreciate what a triumph AAS’s software programming was.  As can be heard on the demo tracks available on the AAS web site, they really managed to make mathematically-generated guitar sounds authentic.

Of course, it doesn’t sound quite like sampled guitars.  There are no fret board squeaks.  The tuning is perfect.  Overall, maybe it sounds a little too clean to be completely realistic.  Some will consider this an advantage and others maybe not so much.

Then there the on-board effects.  These differ somewhat in Acoustic and Electric, as might be expected.  For Acoustic, we have a multi-effect module that offers delay, chorus, flanger, vibrato, a couple of “wah” effects, a notch filter and reverb.  Electric has most of that plus a module for specifying amp and cabinet characteristics, with a spring reverb thrown in for good measure.  Reverb is replaced with tremolo in Electric.

Acoustic and Electric both have a generous selection of factory presets allowing one to rapidly set up both guitar sound and playing style.  If upon first reading through the documentation you feel a bit intimidated about how you’d program the instrument (and there is quite a lot to digest), just relax.  The factory presets give you enough to work with that you may never feel the need to create your own sounds.  And they certainly can serve as starting points for a bit of modest tweaking when you can’t find the exact sound you’re looking for.  For Electric, AAS has thoughtfully provided DI (direct input from the pickup) presets.  Owners of full guitar packages such as Amplitube or Guitar Rig will probably prefer to go with the amps and cabinets of the guitar package rather than the more limited on-board options, and the DI presets are just the ticket in this case.

Is Strum for You?

If you are a keyboardist with little or no guitar skills who wants to sound like an authentic guitarist, then there’s no doubt that either Strum Acoustic or Strum Electric is worthy of your consideration.  Do you want to be able to blast out a brilliant riff that sounds like it was played by Eric Clapton?  Then maybe a better solution would be to buy a guitar and practice for, say, 10,000 hours.  But if your aims are only a tiny bit more modest, Strum is going to be a much quicker way to achieve your goals.  Make no mistake –  it will take some effort to learn to use Strum effectively.  But Strum will probably get you to an authentic sounding style more quickly than learning to mimic a guitar player with convention keyboard “moves”.

It’s amazing just how much an accomplished Strum keyboardist can actually pull off using this technology.  AAS has a video in which a professional player demonstrates what can be achieved.  The video is embedded here for your convenience:


In my opinion, the Strum instruments are great pieces of gear.  The only thing I’d like to see that’s not there would be the ability to use just the front or back ends independently, especially with Acoustic.  For example, using the front end to output guitar-like MIDI to a clavichord or buff-stopped harpsichord sample player could be magical.  And, yes, it might be very nice to be able to play classical favorites on the keyboard and have the back end treat the MIDI input like a conventional MIDI instrument would.  Bach preludes on an acoustic guitar would sound quite appealing.

Both Acoustic and Electric are available as VST and RTAS formats on the PC and VST, AU and RTAS on the Mac.  At this time 64-bit versions are not available for the Mac, although 64-bit versions are promised.  AAS software does not require a dongle, but activation is easier if the computer has an internet connection.

Both instruments have a list price of $199 USD and a bundle with both lists for $299.  However, AAS has been known for the occasional sale in which the prices are reduced by as much as 50%.  A little patience would be well-rewarded in this case.

For further details and to purchase Strum, visit the AAS web site here:

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