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Izotope Iris

Software Synthesizer
Published July 2012
By Paul Nagle

Izotope's Iris offers a new take on sound design via its innovative sample resynthesis engine.

Iris's main screen: the effects of using the brush tool on the spectrogram can be seen by comparing the original (white) waveform and the processed (yellow) waveform.

Izotope have previously earned much respect for their restoration and mastering suites, so on the face of it, the release of a synthesizer seems like a new direction. Actually, Iris is described as a "sampling resynthesizer”, although sampling is not provided — you'll have to do that elsewhere. Instead, Iris (I'm going to resist saying 'she') features a set of enhanced visual editing tools not a million miles from those of the RX2 audio repair toolkit. Here the tools' purpose is not to sanitise errant audio but to create entirely new waveforms via resynthesis. Iris is, therefore, that rare but desirable creature: a source of new sounds that are not easily pigeonholed.

Iris Opens Up

The main screen is dominated by a large central display providing two overlaid views of the source audio. The simultaneous image of waveform and spectrogram, with a slider to blend seamlessly between them, proves both effective and informative. It's more informative still when you enable the display of frequency and time on the two axes; oddly, they aren't present by default. In the spectrogram, the lowest frequencies are shown at the bottom and the brighter areas represent the strongest levels.

Around the display are fold-away views such as the Global sample view, the Synth parameters, the selection Tools and the Keyboard. Each Iris patch can contain up to three samples plus a sub-oscillator, and these sources have their own coarse and fine tuning, pan and gain. A handy pop-up window enables allocation of different keyboard zones for each sample. Select the 'All' view to see (and edit) all the current samples and the sub-oscillator on a single screen.

It's worth emphasising that four sources are the limit: there's no multisampling or resampling. Iris is about resynthesis, not realistic sample playback, something you quickly realise when you transpose any sample too far from its natural pitch.

The Main Draw

Proof, if it were needed, that my face sounds better than it looks — with apologies to Aphex Twin!

The best introduction to Iris's charms involves first dragging in a sample, either from the library provided or from your own collection (wav or .aiff files are supported). The supplied samples are all in a proprietary format, but can be previewed before loading, thanks to a rather elegant little browser. Iris can attempt to automatically choose a root note for the sample based on an analysis of its content, but it's an easy matter to change this later by simply dragging the root pop-up.

Once a sample is safely on board, it's time to begin making selections using the wide range of tools supplied. Perhaps the easiest tool to start with is the Lasso, as this enables you to draw any shape you like in the spectrogram's time/frequency field. Draw at the bottom to capture low components and at the top for the high stuff, or make slanting lines for gradual harmonic transitions. If you've used Photoshop or similar drawing packages, this kind of selection will feel very familiar. If you have the waveform visible, the resulting selection is shown in yellow, laid over the original waveform in white.

As you add further selections, auditioning the results on your keyboard as you go, Iris rapidly switches from entertaining to addictive. Other tools inspire their own gratuitous fun — for example, the Brush selector. Set the brush size as required and simply draw freeform over the spectrogram. You can write your name or use whatever artistic skills are at your disposal, while constantly playing with the results.

Idly sketching with the mouse is one thing, but you can make less frivolous selections based on horizontal frequency bands, vertical time bands, or both at once. Making time selections is a good way to break up audio, chop parts of loops etc. Then there's the Magic Wand tool! Under my guidance, this summoned neither rabbits nor Debbie McGee, but instead conjured up similar harmonics to any it recently selected. It even proved effective for plucking related components from a full mix. Then there's an eraser that trims parts of a selection or carves out holes, plus options to grab and drag selections, invert them, and so on. Selection is one of the main activities, so it's good news that there's one undo for the selection tool and a separate one for the rest of the synth.

It's all pretty comprehensive, although, on behalf of the drunk and the shaky of hand, I'd like to request the future inclusion of drawing standards such as ellipses and straight lines. Otherwise, there's little you can't achieve — especially as you can zoom to paint in fine detail.

I think it's worth giving a few more examples of how selection generates its output. Suppose I wanted to mimic the sound of a closing low pass filter: a sawtooth-shaped selection delivers that easily. But there's no reason to stop there. Within the same sample, you can add a further selection containing just a band of upper harmonics, then maybe chop out part of the low sweep with the eraser. I was fascinated by some of the otherwise unheard artifacts found lurking in my own recorded samples, brought to light by selecting very narrow frequency bands.

I should mention that a lot of these techniques are absolutely ideal for remixing — with the proviso that Iris's resynthesis currently imposes a maximum playback limit of one minute per sample.

Wait, There's More

The mix screen shows all parameters of the four sound sources at once, plus the effects and filter.

Looping is simple and painless, with crossfade looping on hand to smooth out any awkward sources. Every worthwhile playback direction is catered for too (forwards, backwards, forwards then backwards, backwards then forwards, one-shot and reverse one-shot) while just three options determine sample pitch. These are: Resample, Radius RT and Fixed. Resample is typical sample playback, while Fixed maintains the same pitch and playback speed regardless of the triggering note. Radius RT uses considerably more CPU power than the other modes and also limits the number of notes that can play at once. The default is four, tweakable up to 10.

Radius RT performs real-time pitch-shifting, which gives +/- two octaves of transposition at its default setting. You can increase this, but I found that beyond three octaves, small artifacts were often created. Radius RT has a 'high quality' mode in which it grabs even more CPU power, and this brought a noticeable improvement in sample clarity, but for most synth patches I found it unnecessary.

Current polyphony is indicated in the Voice Mode window, and the choice of using either RT or standard resampling plays a major role. You are typically given 10 voices to play with, although this can be increased, with a corresponding CPU cost. Generally, I found performance good, provided I used RT mode sparingly.

Sadly, there is no way to change the playback speed of a sample independently of its pitch, nor is there much you can do timbrally as samples are transposed over the keyboard. You should, therefore, expect some 'munchkinisation'. I can't help but recall Roland's Variphrase from over a decade ago and its various 'elastic audio' techniques for sample stretching. It's a pity there isn't something comparable here.

Fortunately, after that one disappointment it's all plain sailing. You can choose whether new notes trigger playback from the start of the selection or from the position of the last held note. Each sample has a simple ADSR envelope with a maximum release time of 30 seconds, plus an LFO to modulate pitch, level or pan.

Before moving on, I mustn't neglect the fourth sound source, the sub-oscillator. This is equipped with all the usual synth waveforms, plus noise. Interestingly, if you copy any of the factory samples into the Sub waveform folder, they become Sub waveforms too. So although you can't load regular samples, there's scope to add yet another layer, if you feel so inclined.

Polish & Performance

A varied set of selections made by combining the lasso, magic wand and frequency tools.

Traditional synth sculpting tools include a global multi-mode filter with a dedicated envelope. This filter has several analogue models, including saturated valve types, and makes a worthy contribution to polishing the resynthesized audio. There's a global LFO too, acting on the filter cutoff, amplitude or pan, while performance-based modulation is equally direct and consists of pre-configured velocity and aftertouch routings. Naturally, you can assign MIDI controllers extensively across the board.

For convenience, the Mix view gathers all Iris' synthesis parameters on a single screen, along with the filter, effects and macros. Macros are a set of eight common parameters that are applied universally, with an X/Y pad to manipulate them. Izotope have included a number of preset macros to quickly transform your creations into solo patches, pads and so on.

Last up, the effects implementation is uncomplicated, but no worse for that. It works in serial or parallel mode and offers reverb, delay, chorus and a versatile distortion. In parallel mode, each sample has independent effect sends, which is flexible enough for most eventualities.

The Library

The browser for patches and samples is bang-on for speed and usability. As well as categories for Ambient, Bass, Percussive, and so forth, there's a User category, although happily you're not prevented from adding entries to any existing category.

The supplied patches are a strange bunch that go from the spiffy to the iffy in a matter of mouse-clicks. Most impressive of are the sound-design types that crop up in most categories to showcase Iris's depth and complexity. We're talking fantastic, evolving atmospherics and other-worldly textures here! There are some decent pads and vocal tones included too, but it's when you turn to the Keys, Leads and Retro categories that the cracks begin to show. The synths are often lifeless, while the other instruments derived from pianos, strings, mellotrons, and so on, vary from a bit cheesy to awful. This isn't to say you can't make usable synths, basses and leads, just that it clearly isn't so effortless as the outlandish stuff.

The library's 4GB of samples includes everything from the noises of machines and nature to classic synths, guitars, and even toys. Nevertheless, I think that Iris best ignites the imagination when unleashed on more personal audio.


Iris is a sound-designer's dream come true: it's sample resynthesis made into an art form. The spectral selection works like magic and is so inviting that within a matter of minutes, all you want to do is poke around in samples looking for treasure. The basic concept of layering selections, filtering them and adding effects translates to minimal diversion from hatching fresh sounds. Only the lack of time control over sample playback imposes limits that occasionally feel frustrating.

Of the included patches, it's the more experimental and abstract that really impress. Fortunately, there are plenty of other synths and sample players out there when you want 'normal'. Iris delivers the abnormal like a demonic midwife! Aside from its talent for uniquely weird instruments, there's definite remix potential. I know of no other sample-playing plug-in that makes it so straightforward to reshape an audio source. The only downer (or challenge) is that playback is currently limited to one minute, to conserve memory. Hopefully, that's something that might change in the future.

Ultimately, Iris is a treat for the experimenter, and should instantly appeal to film composers seeking previously-unheard textures. Highly recommended.  


Not too many purely resynthesis-based instruments come to mind, but Camel Audio Alchemy offers resynthesis, additive synthesis, granular and virtual analogue synthesis — and probably descales kettles and rods drains too, if you know how to ask! An Alchemy owner myself, all I'll say is: Iris only does resynthesis, but does it beautifully and intuitively.

Try Before You Buy

Iris runs either as a stand-alone application or as a plug-in you can try without restriction for 10 days, after which the demo mode kicks in. Assuming you're suitably impressed, there is a choice of authorisation methods — either a challenge/response type or iLok‑based. Having taken your pick, you are then free to download the full Iris sound library, which includes around 500 patches and over 4GB of samples. Here, the Mac installation was a bit of a drag because, for no good reason, it insists you place the entire library on a system disk. I say "no good reason”, because you can move the library manually, post-installation, updating the location within Iris, which is probably the first thing most users will do.

System Requirements

  • Windows (XP Service Pack 2 or later, x64, Vista, 7).
  • Mac OS 10.5.8 or later (Intel Macs only).
  • Plug-in formats: Stand-alone application, Pro Tools 7.4+ (RTAS/AudioSuite), VST and VST 3, Audio Units.

The review system was a Mac Pro 2x2.66GHz quad-core Intel Xeon with OS 10.6.8 and 12GB RAM, running Logic 9.1.7 in 64-bit mode. Iris runs as a stand-alone application, or as a Pro Tools 7.4+ (RTAS/AudioSuite), VST/VST 3 or Audio Units plug-in.

Published July 2012

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