Applied Acoustics Systems Chromaphone
Tue, 10 Apr 2012

By Jim Aikin

xylophones, bongo drums, chimes, gongs, plucked strings, and more. This plug-in synth uses physical modeling to produce a wide variety of struck and plucked instrument sounds. Some are amazingly realistic, others so exotic they could come from another planet. The tone is detailed and musical, but I wouldn’t call it fat. No samples are employed—all of the sounds are synthesized in real time. This adds expressive power, especially in the velocity response, but a fast computer is highly recommended.

Chromaphone is not an especially deep or complex instrument. It’s not packed with hidden options: A glance at the front panel says it all. The synthesis engine is not your standard oscillator/ filter layout, however. When you start designing your own sounds, you’ll find that the controls interact with one another in unusual ways. There’s more sonic power here than meets the eye, and a bit of trial and error may be needed to get the sound you’re searching for.

At the root of Chromaphone’s modeling are resonators (things that vibrate) and exciters (things that strike or pluck the things that vibrate). On the left side of the panel are two sources for excitation signals: a mallet and a noise generator. The signal from these is sent to a pair of resonators. Depending on what resonators are used and how they’re programmed, a simple excitation signal can produce a huge variety of tones. Eight different resonator types— string, beam, marimba, membrane, plate, closed tube, open tube, and manual—are provided.

Rounding out the feature set are a vibrato LFO, a general-purpose LFO, and a pair of effects processors. The 20 effect types include all the things you’d expect, from chorus and reverb to tremolo, EQ, and overdrive.

Modulation depth is displayed in pale colored arcs around the knobs, and also numerically when the depth is being edited with the mouse. The pale arcs are a bit fiddly and hard to see, but overall the user interface is very sensibly designed: Inactive controls are grayed out, modulation depth can be zeroed by double-clicking, a preset browser is tucked away under the Manage button, and so on.

The mallet source produces a brief impulse at the start of each note. It has four knobs: Volume, Stiffness, Noise amount, and noise Color. The first three can be modulated by key number and/or velocity. When the stiffness is low and the noise amount is high, a softly brushed attack is produced. When the stiffness is high you get a snappy attack.

In addition to the noise in the mallet source, Chromaphone has a second, more flexible noise source. Its main purpose is to give you an ongoing signal that can generate sustaining sounds. It has Volume, Frequency, Q (width), and Density knobs. The Frequency and Q knobs control a multimode filter that processes the noise signal, and this filter has its own five-stage envelope, with a delay segment upstream of the expected attack, decay, sustain, and release.

A low setting for noise density can produce a pleasantly randomized repeating attack, reminiscent of wind chimes. I spotted a minor bug in the version 1.00 release, however, that causes extremely low settings for this knob to shut off the output of the noise source. I’m told this bug is only in the Windows version. The volume, filter frequency, and density of the noise can be modulated by key number, velocity, or the LFO, and both frequency and density can be modulated by the envelope.

Using the Direct slider, you can mix the signal from the sources straight into the output, bypassing the resonators. This is useful for hard attack clicks, wind noise, and probably a few other things.

The resonators are the heart of Chromaphone. They can operate in parallel, providing two independent resonances from the same excitation signal, or they can be coupled. When they’re coupled, the output of resonator A feeds the input of resonator B, but there’s also a feedback loop, causing B to add energy back to A. This emulates the behavior of physical instruments. In an acoustic guitar, for instance, the energy of the vibrating string flows into the soundboard, but the vibration of the soundboard also affects the vibration of the string.

The balance/coupling slider at the far right of the screen controls the volume balance between the two resonators when they’re not coupled, and their relative stiffness when they are coupled. The position of this slider can be modulated positively or negatively by MIDI note number. It has a surprisingly large effect on the tone.

With a couple of exceptions, the resonators each have five knobs: Decay, Release, Material, Tone, and Hit Point. They also have inputs for LFO modulation and a built-in pitch envelope with amount, decay time, and velocity response sliders. The exceptions are the closed tube and open tube, which only have knobs for Decay, Release, and Radius (i.e., how big around the tube is) and don’t allow LFO or pitch envelope modulation.

Also omitted from the tube models is a fourposition complexity switch. With this switch you can control the number of partials that will be generated by the resonator. More partials will give a more complex and realistic tone, but at the cost of some extra CPU usage.

Pitch modulation in Chromaphone can occasionally cause undesirable behavior. With either LFO modulation or a pitch envelope, a resonator can go into runaway digital overload, resulting in a really loud and nasty sound. This doesn’t happen often, but it happened more than once while I was working on this review.

The Material knob models the difference between rigid and loose materials by adjusting the decay and release times of the higher partials in relation to the lower ones. When the material is stiff , the high overtones last longer; when it’s less stiff , the high overtones die out faster than the lower ones. The tone knob does something similar, balancing the basic amplitudes of higher and lower overtones rather than off setting their decay times.

The Hit Point knob adjusts the physical location in the model at which the excitation signal interacts with it. With a string model, for instance, this knob gives a realistic impression that the string has been plucked nearer the bridge or nearer the middle. The tube models don’t have a hit point, because a signal can enter a tube only at its end—think of a flute or pipe organ. Decay time can be modulated by MIDI key number, and hit point by key number, velocity, or a random source.

Pitch Control
The two resonators can be tuned independently, and the pitch of each of them can track the keyboard fractionally. Some of the most interesting percussion sounds in Chromaphone are achieved by detuning and fractionally scaling one or both resonators. With the manual resonator, you have independent pitch control of four sine-wave partials—and they aren’t restricted to whole-number multiples of the fundamental pitch, so bell tones and other things with interesting harmonics are easy to program.

The tricky aspect of fractional keyboard pitch tracking is that when the resonators are coupled, they will be much more in tune with one another on some keys than on others. This can cause certain notes or keyboard zones to sound much louder and with more sustain than other notes or zones. This isn’t a defect; it’s the nature of physical modeling.

Chromaphone can’t load alternate tuning tables. For an instrument that does a fine job with metallophone timbres such as you might hear in a gamelan, this is a significant omission.

Incredible as it may seem, Chromaphone does not respond to MIDI pitch-bend. Given the possible instability of a physical model when the pitch is being modulated in real time, and given the fact that you can’t pitch-bend a marimba or a gong while it’s sounding, I’m almost (but not quite) willing to give Applied Acoustics a pass on the absence of pitch-bending. The pitches of the resonators can be automated in your host sequencer, so you can draw bends or “play” them in with a controller if you need to.

Factory Sounds
More than 300 presets are included with Chromaphone, in a dozen categories. Not surprisingly, they’re strongest in the mallets and chimes departments. One of the categories is called “Kits,” but this is something of a misnomer as Chromaphone lacks the multitimbral keyboard mapping that’s normally required for a drum kit. The Applied Acoustics website says that Chromaphone comes with “ready-made creative kit patches where each note provides a new sound slightly different from the previous one. Over the entire keyboard range the sound morphs from bass drum to snare to hi-hat.” The sound does indeed morph—mainly due to keyboard scaling of the Pitch and Hit Point parameters. The end result, though, is glitchy sounds that, while they might play the roles of kick, snare, and hi-hat in a rhythm track, sound neither like real drums nor old drum machines. Listen to the “Chrompahone Kits” audio clip I posted online and judge for yourself.

The electric pianos don’t sparkle as much as I’d like, but the Clavinet has a nice bite. The bongos, clay drum, and high tabla are crisp and useful. The “Woody E. Bass” and “Velo-Slap Bass” are satisfyingly full-bodied, but I felt some of the other basses were trying a little too hard. The patches in the “Strings & Pads” category are breathy or raspy, because they use the noise source to create a sustaining tone.

In the “Plucked Strings” bank, “Electric Contemplation” has a rich hollow-body electric tone, “Soft Harp” does the job, and “Inverted Dulcimer” has the kind of crazed edge you’d expect from a prepared piano. Chromaphone does a nice job with organ pipes, thanks to the tube resonators and the noise source.

Chromaphone delivers a surprising variety of expressive sounds, and gives musicians some unusual and useful kinds of control. I’m not a big fan of velocity cross-switched multisamples (and Chromaphone doesn’t use them), so I’m especially pleased with how smoothly and naturally Chromaphone responds to velocity. Programming your own sounds in a physical modeling synth can be a bit intimidating at first, but coming up with evocative new sounds turned out to be far easier than I expected. Chromaphone is a specialty item, not a do-everything workhorse synth, but it’s sure to find a home in many studios.

Snap Judgment

PROS Great for chimes, mallets, and pipes. Expressive velocity response. Detailed tone colors with unusual types of control.

CONS Doesn’t receive MIDI pitch-bend. No alternate tuning tables.

Bottom Line

Realistic physical models of struck and plucked instruments, with lots of ways to tailor the sound.

$199 list | $185 street

Key Info


Physical modeling.

FORMATS VST or AU plug-in.

SYSTEM REQUIREMENTS Mac: OS X 10.5 or later. PC: Windows XP SP2 32-bit or Windows Vista or 7 32- or 64-bit. Both: 512MB RAM, 70MB free hard drive space, 1024 x 768 display resolution.

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