Review – The Loom Additive Synth from AIR Music Technology

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Additive synthesis is a fascinating method of producing sound, but additive sound design is a considerable challenge.  Or is it? Now there’s Loom and that storyline is changing.  We take a close look here.


by David Baer, Mar. 2015


Additive synths have been around for a few years, and there are some notably cool instruments in this category.  These include Alchemy (let’s please have a moment of silence in sympathy for all Alchemy fans who use PCs), NI’s Razor, and not just one but three instruments from Image-Line: Morphine, Harmless and its big brother Harmor.  And those are just the one’s I own.

The instruments on that list have several things in common, not least of which is that they produce some really exciting sounds.  Also not least of which is the fact that additive sound design from scratch is a dark art.  Alchemy and Harmor both offer a resynthesis capability that will allow one to analyze an audio clip and create an additive mapping from it.  They also both offer a fascinating sound-from-image capability.  But you don’t just sit down and start manually defining the minutia of additive sound parameters and expect to get anywhere quickly.

But there’s a new additive synth in town that gives us a motivation to actually build sounds from the ground up.  It does this with a unique user interface that’s unlike anything I’ve yet encountered.  Some capabilities found in other additive instruments are sacrificed in the process, but the result is quite viable, as we’ll see.

We’ll start with a review of additive synthesis for those not especially grounded in the subject.  Those with a good knowledge in this area may wish to just skip the next section.


Additive Synthesis 101

Any single-cycle waveform can be broken down into discreet component sine waves, one at the fundamental frequency, and others at integer multiples.  There are theoretically an infinite number of such sine waves, known as partials.  In practical terms, you only don’t need any partial with a frequency above the Nyquist frequency (or one-half the sample-rate) to produce a credible result.  So for low bass notes, you might require 200 or more partials, but that number diminishes the as the frequency of the sound gets higher.

But pitch is only part of the story.  Each partial also has a phase relative to the fundamental.  The sine wave cycles of the partials do not have to start in sync, although there’s no rule that they cannot.  Standard subtractive waveforms like sawtooth and square have partials that are completely aligned phase-wise.  Triangle is a little different.  Those partials that are present alternate between exactly in phase and exactly 180⁰ out of phase.

When partial pitch and phase is constant and all partial frequencies are integer multiples of that of the fundamental, the associated sound is that of a single-cycle waveform repeating.  If however the partials are not integer multiples, then the each individual cycle is different from the one before and the one after.  As the partial frequencies drift further from integer-multiple frequencies, the sound becomes dissonant and/or metallic.

Additive synthesis is the creation of sound by adding sine wave partials to create a resultant audio stream.  Once the audio stream is thus created (i.e., all the partials summed into a single audio signal) and passed along for further processing, such as to an effects section, there’s no longer anything special about the additive nature of the process.  But before that happens, characteristics of individual partials can be manipulated on a per-partial basis, and this is the way in which additive synthesis offers unique possibilities.

It’s common to refer to partial manipulation in this fashion as operating in the frequency domain.  As long as processing remains in the frequency domain, manipulation of the characteristics of individual partials is possible, and this is where things start to get interesting.  Just as one example, we can pan partials variously to different points left-to-right to achieve very interesting spatial results.  Furthermore, we could animate that panning so the sound evolves as we listen.  Manipulating/modulating while in the frequency domain is what gives additive synthesis its unique character.  You can do some things in this fashion that simply cannot be done with other kinds of synthesis.

Some types of manipulation are fairly easy.  For example, a high cut filter can be achieved by attenuating partial levels above the cutoff according to the filter characteristics desired.  But manipulating partial phase settings over time, to cite a different example, can involve a lot of tedious specification.  Or it can mean fiddling with a number of largely incomprehensible controls.  It is for these reasons that additive synthesis has a reputation of being challenging in terms of sound design.


The Loom Approach

As stated earlier, Loom distinguishes itself from the pack in that it requires relatively little training to accomplish some effective sound design.  Part of the reason for this is that it hides, or flat out doesn’t support, certain additive details like partial phase specification (whether that sort of thing actually is happening under the covers is not clear).  Another part of the reason is that Loom offers a very visual and intuitive sound design space in which to work, one in which sound manipulations can be not just heard but the effect of the manipulation can be observed on a spectrographic breakdown of the audio.

Loom has two tabs: Edit and Morph.  We’ll be concentrating on the Edit tab for most of this discussion.

Loom has twelve slots on the edit tab into ten of which can be placed sound generator or sound modifier modules.  The first slot is fixed and we’ll return to its purpose shortly.  The final slot is an FX bin.  What goes in between slots one and twelve is up to the sound designer, but there are two general “givens” that can be seen in most of the factory presets.  A partial generator normally goes into the first open slot (slot number two) and a gain control normally goes in the last open slot (slot number eleven).  In the screen shot at the top of this article, we see a preset that utilizes all but slot number six.  However, most of the factory presets aren’t this complicated.

Each insertable module, whether it produces or manipulates component partials of a sound, has a common form.  Let’s take a close look at the filter module, pictured left.  There is one knob which is the primary control.  In this case, it is frequency, which makes sense for a filter, of course.  This parameter may be modulated with any combination of an envelope, an LFO and a MIDI parameter.  Other controls are present but are not modulation targets – not in a programmable fashion anyway, but we’ll see when we look at the Morph panel that some of these may be manipulated in real time.

To the right of the knob are other parameters.  In the filter module these are emphasis (resonance), emphasis width, filter Slope and key tracking amount.  Beneath these are the modulation assignments.  In pictured example, we see frequency modulated by envelope 2, LFO 2 (depth of LFO being controlled by mod wheel) and aftertouch.  In this case, all are positive modulations, the depths of which are approximately 20%, 50% and 35% respectively.

On the bottom we see a spectrograph of the partials.  This is an “after” image.  When a note is depressed, you can see how the sound character is being manipulated by each successive module.

The AHDSR envelopes and LFOs are nothing unique, but envelope 4, labelled Slope and pictured right needs a little explanation.  With it you can specify an initial level, attack time (the time it takes to return to neutral position), sustain slope (after attack phase ends and until note release) and release slope.  If the pictured envelope were applied to pitch, the pitch would begin low and rise to correct pitch; then it would start to drop until note release.  If the note were to be held long enough, the pitch would drop to sub-audible frequencies.  Upon release it would rise more rapidly than it dropped.

Let’s return to the first insert module and also discuss what’s going on in the fixed slot number one.  The first insertable module is nearly always (at least in the factory presets) called Odd/Even.  Basically, it’s a partial generator that produces a saw wave at knob position 12 o’clock.  Fully clockwise is a square wave and fully counterclockwise a pulse.  There are several other partial producers, but Odd/Even is the one you usually find in slot number two.  The other generator modules include two different “Organ” partial generators and a limited resynthesis module known as “Wave” (limited, that is, compared to the resynthesis capabilities in Alchemy and Harmor).



Fixed slot number one is used to specify spectral distortion (manipulation of partial frequencies) and modulate that distortion.  An in-depth discussion of how this works is beyond the scope of this review.  Suffice it to say that slot number one “reaches into” slot number two and does stuff in a variety of ways to the distribution of the partials.  The image to the right shows the types of distortion available, but the names probably mean little.  To my mind, this is one of those “set by ear” controls.

The Odd/Even module and Gain module are one of seven in the category of Basic Modules.  Other module categories are Filtering, Effect, Rhythmical, Time, Tools and Wave.  There are quite a few modules from which to select.  In the Filtering category for example, we have eight choices.  These, at least, will be familiar territory for anyone with a modest amount of synthesizer expertise.  Other categories are rather more esoteric.  The two Rhythmical modules, for example, are Phrase and Random Drops.  No clue as to what those do?  Time to check the documentation.

Oh no!  And that brings us to the most disappointing aspect of Loom.  It has the saddest excuse for documentation that I’ve ever seen with any synth.  Screen-based help is available for many of the interface elements, but that’s it, and that isn’t even all that helpful much of the time (and to add insult to injury, the font used is rather difficult to read).  The PDF manual that comes with the instrument not only fails to explain what the various modules do, it doesn’t even bother to list what modules are available.  One saving grace, for those who happen to have a Groove 3 all-access pass, is that Groove 3 offers a reasonably in-depth video course on Loom which I can highly recommend.

At least the presets that come with the instrument offer much variety and can often easily be reverse engineered to start to understand Loom sound design techniques.  The other thing going for Loom in this area is that it’s truly easy to just start playing around, trying this and that.  You can actually get some pleasant-sounding results through experimentation.

But we must move on to other things.  It would take pages and pages to properly cover all the aspects of the Edit tab modules.  But to do so is way beyond the scope of a simple review.


The Mighty Morph Tab

Let’s instead turn attention to the other main tab, Morph.


Here we have what I regard as some very insightful and elegant design decisions for the instrument.  Along the top we have a row of knob controls, categorized as Sound, Dynamics, Modulation and Master/FX.  Each of these controls is hard-wired to a variety of controls within modules on the Edit tab.

You, as sound designer, do not get to choose what those mappings are or what the depth of the target parameter alteration will be.  The Loom designers have done that for you.  If an association exists to a module parameter and you insert that module type in a slot on the Edit tab, the parameter will be manipulated, period.  On the whole I think this is actually a positive.  Additional control might be nice, but having the decisions pre-made and you being given no choice in the matter, you may very well benefit in considerably faster sound designing.  So, Tone, for example, controls Cutoff within the filter module, but almost certainly will also control other parameters in other modules.  This, of course, is not documented in the slightest.

Any of the Morph-tab knobs can be MIDI-learned.  What’s especially nice is that you can dictate what range limits of the knob.  For example, you could have a slider on your MIDI keyboard controller move a knob between the 10 o’clock and 12 o’clock positions using the full range of slider movement.

The area in the lower left is the Morph area, and it’s far more sophisticated than an ordinary XY controller.  With each corner (A thru D) you may define a set of Morph-tab knob positions.  You may seamlessly move with your mouse between these within the control area and, as advertised, the sound will morph accordingly between the corner settings.

Even better, you can animate these movements in a rather sophisticated fashion.  Not only can you define multiple segments for a path of movement, you may also individually set relative per-segment speeds of movement.  Overall speed is adjustable and host temp-sync is supported.  All in all, the morph tab delivers a lot of power.

Lastly on the Morph tab, we have a large spectrograph partial display in the lower right.  This is the same information shown in the final insert module, but it’s much larger.  To check out what’s going on with a sound in detail, just click over from the Edit tab to the Morph tab, and all is revealed.


Is Loom for You?

Loom is available in all major formats for PC and Mac, but is 64-bit only.  I suspect this is something we’ll be seeing more and more of in the near future.  No iLok or the like is required and I recall no difficulties with activation.

The retail price is $150 USD, but since its introduction there have been several sales in which the price was one-third of that.  At full retail price, the instrument is overpriced in my estimation.  For not much more money one could acquire u-he Zebra or Rob Papen Blue 2, and Loom is not in that league in my opinion.  However, for $50, it’s quite an attractive option, especially if you either have no other additive instruments or are looking for one with which mere mortals can design sounds. 

Initially, AIR chose to not offer a downloadable demo version – probably a choice that didn’t sit too well with potential customers.  They evidently reconsidered and have announced that a demo download will be forthcoming.  However, at the time of this writing  it is not yet available.

Loom does sound digital, but that’s a quality attributable to additive synths in general.  In spite of that, there is plenty of capability for fat, rich sound creation.  There are some excellent demo tracks at the AIR web site that show the range of what this instrument can do.

One final caution is in order.  It’s my understanding that AIR until recently was a Pro-Tools-only shop and that heritage was evident when I installed the software.  The Loom install process did some rather annoying things such as installing the AAX format module without asking and not allowing me to dictate where the VST was to go.  Hopefully this will have improved due to customer feedback, but if the install gives you the choice of custom vs. default installation, play it safe and go with custom.

For more information and to purchase Loom, go here:



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