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Occasional posts on subjects including field recording, London history and literature, other websites worth looking at, articles in the press, and news of sound-related events.

05 May 2011

Seeing sounds: Izotope RX2 as a wave editor

IZOTOPE RX2 IS a professional standalone audio restoration program aimed at recording studios, broadcasters, sound archivists and audio forensics experts. It isn’t designed as a wave editor, but many of its features might make it attractive to field recordists for just that purpose.

Recently my copy of Wavelab Elements 6 was written off by a trial version of Comodo Internet Security, which sandboxed Wavelab’s Syncrosoft electronic license. Gutted! So I’m using Izotope RX2 as a replacement. Here’s what it can and can’t do compared to a budget wave editor.

Wave editors display sound files as two-dimensional waveforms, showing changes in amplitude or loudness over time. Izotope RX2 instead renders the recording as a spectrogram with three dimensions of information: time, amplitude and frequency. The spectrogram is constructed very quickly and a fascinating amount of detail can be seen. Here’s a screenshot of a recording featuring the calls of several different bird species:

Izotope RX2 screenshot


A much bigger version of the screenshot is on this page and it’s worth looking at to get an idea of the spectrogram’s resolution and the delicacy of the features revealed. At that zoom level, individually numbered seconds start appearing, but you can go in a lot closer.

Navigation is straightforward both in the main window and the overview strip at the top, although unfortunately there’s no ‘go to the end’ button. Markers can be added by tapping the ‘m’ key. Doing this with a selection turns it into a region with start and end markers, and annotations can be added to a small pop-up window.

The spectrogram is very useful when it comes to reviewing long recordings and getting an idea of the sequence and structure of the sounds within. It’s better than relying on an amplitude waveform alone. Being able to identify particular sounds and their precise frequency ranges also encourages experimentation with Izotope’s 4-band parametric equaliser, with has high- and low-pass filters plus adjustable notch filters.

The five audio restoration modules in the program are Declip, Declick & Decrackle, Remove Hum, Denoise, and Spectral Repair. Declick & Decrackle probably doesn’t have much relevance to the needs of most field recordists – no, it can’t do anything about the rustle of plastic carrier bags – but obvious uses can be found for the rest, especially Declip and Spectral Repair.

Here’s an Izotope promotional video for the Declip function:


The Spectral Repair module is the most intriguing. A much cheaper program called Magix Audio Cleaning Lab also has a spectral repair function, but it’s nowhere near as well-implemented as that on Izotope RX2. Spectral repair allows you to attenuate brief and inconvenient noises very precisely, or even replace them with background sounds found elsewhere in the recording. It’s analogous to the ‘intelligent spot healing’ tool in Photoshop and uses similar selectors such as a paintbrush, magic wand, and lasso.

Here’s a demonstration of spectral repair facing the admittedly favourable task of having to remove a brief, high-pitched and distinctive sound:


Should field recordists use spectral repair on recordings that will later be described as actuality? Such a question can only be answered by the individual recordist according to their own intentions. One of the goals of this site is to strive towards a neutral and depersonalised sound record of London, even if that is only a continually-receding mirage. So I think it’s acceptable to use spectral repair to get rid of my own inadvertent self-made noises such as the chink of unwrapped coins in a pocket or the sound of a twig snapping underfoot. Of course, far better to avoid making such sounds in the first place.

Now for the bad news. At around £185 RX2 isn’t a particularly cheap program, and many may feel that money would be better spent on upgrading from Audacity or a cheap wave editor to something like Pro Tools or the new version of Adobe Soundbooth – sorry, Audition! Also, you can’t use third-party plug-ins with the standard edition of the program. That feature is reserved for the high-end RX2 Advanced version and your heart will collapse into a heap of sand when you see the price. Judging by comments on various web forums, not everyone was overjoyed by Izotope’s decision on this.

RX2 makes fade-ins and fade-outs as easy as they should be, but it has no crossfade feature. The program can import a variety of file formats, but will only export to WAV and AIFF. There are a couple of ways you can get around this without having to open up files in a wave editor to convert them and add ID3 tags. The paid-for version of MediaMonkey allows tagging and converting or, for a cheaper option, you can use the free JetAudio player with its paid-for MP3 encoder at around £6.

If you’re curious, you can try out the save-disabled trial version of Izotope RX2 to see how you get on with it.