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iZotope RX4 repair software

Issue #29

Some years ago I was given some tracks to mix. The recorded performances were excellent but there was a distracting rumble all over the recordings. I tried filtering and EQing and gating but got nowhere useful, and after wasting several hours I called a friend to ask if he had any ideas. He told me to send the tracks over and the following day I got them back, clean and clear. Of course, he wouldn’t tell me how he did it - it took many beers before he admitted that the job had taken him ten minutes with a thing called RX.

Audio recordings are horribly prone to catching sounds that we didn’t want and that no-one noticed at the time, or just didn’t have the time or energy or ability to fix. Classic examples are buzzing amps, air conditioning noises, traffic (I’ve had a helicopter hovering overhead for 45 minutes and not noticed until I listened back to the recorded tracks), dogs barking, drummers falling over, chairs creaking, someone shouting “YEAH!” as the last note of the best solo the guitarist’s ever played is dying-out, video camera noise, room ambience, mobile phone chirps - the list of even common ones is frighteningly long. Here’s the odd thing; most of those listeners who’ll never notice when you do something really clever to make a recording sound great will register instantly the moment there’s something wrong, and it’s a heck of a lot more difficult to fix it than it is to mangle it.

There are some basic tools that you can use to remove or reduce noise but the big problem is getting enough of the noise out of the result without doing too much damage to the audio that we want to keep. This is one of those areas where a dedicated tool can not only save time, but can also help us to do things that we simply can’t manage with standard audio tools. Noise reduction tools tend to work by sampling noise and then removing it, or by applying profiles of known types of noise which you then fine-tune to suit your recording.

Enter RX-4!

RX4 is the latest version of that suite of restoration software from the clever folks at iZotope. There are two versions, the standard and the Advanced package. I’m going to look at the standard version here as it contains the core functions that are useful in everyday life, and box-out the highlights of the Advanced version. There’s a lot in RX, so I suggest taking a look at this article’s video to see what it looks like and to get an idea of how it works.

The programme can run standalone or as a plug-in in your DAW or NLE (Non Linear Editor); I’m going to work through the stand-alone version here because I think it’s easier to get an overview that way - the functionality is there in the plug-in version too; you just choose which components you want to use in the DAW or NLE framework.

The main screen is mainly taken up with a large waveform display, with a toolbar, meter and transport controls below, level and frequency scales and a list of modules to the right and a set of tabs above. The waveform display shows the common outline display of level against time in blue, and also the orange/yellow spectral representation that lets you see both frequency content and level against time - it can be a bit confusing if you’ve never worked with one before, but gives a lot of information, and once you get you head around it you’ll find that you can actually see noises in your audio.

The modules cover specific tasks which are generally clear from the name - if you’ve got a problem with hum in your track you want the “Remove Hum” module, if you’ve got clicks on a vinyl transfer, the “Declick” module will help you, steady background noise on a voice track - try the Dialogue option of the “Denoiser” module, clipping - “Declip” and so on. Spectral Repair takes a bit of practice, but if you think of it as allowing you to paint-over unwanted noise then you won’t be too far off the mark. Alongside the repair functions is a range of useful utility tools including 6 band parametric EQ and iZotope’s own MBIT+ dither and SRC (Sample Rate Conversion) modules which are very good indeed.

Most of the functions are pretty easy to get started with; without reading the documentation you can figure how to load audio then take a pretty good stab at what module(s) you need to fix your problem, and a helpful selection of presets will most likely get you close to where you want to be. If you need more then you can fine-tune and tweak settings to refine your results to the level you need. Incidentally, iZotope publishes an excellent (and free) overview of audio restoration called “Audio Repair and Enhancement Guide” which is well worth reading.

If there’s one major problem with restoration work, it’s knowing when to stop. If we’ve got an unwanted noise that’s distracting, then we need to reduce it to a level where it isn’t distracting - achieve that and our job’s done. Of course, once we start to zoom-in on a noise we end-up getting obsessed with removing it, and too often end-up spoiling the audio that we want to keep. RX4 can’t stop us from doing this, but the interface provides bypass, compare and undo functions that make the workflow about as easy and safe as it can be.

Unlike traditional audio processing where we can do pretty well anything we like, and if it adds “mojo” or “vibe” then it’s good, restoration work has a definite base-line; we can all hear what the initial audio sounds like, and in general we to want it to sound just the same, but without the noise. Of course, there are limits to what can be done, but those limits are a lot further away than they used to be. Restoration work needs powerful and well thought-out algorithms and clear and informative interfaces, and these are areas where iZotope has consistently been amongst the best in the business, and in my experience the RX series has consistently been amongst the restoration software front-runners. The basic RX4 is a powerful and flexible solution that is capable of achieving surprisingly good results with very little effort, and some truly startling results if you take the time to learn how to use it to its fullest capabilities! And once you do, there is the Advanced version which, while a lot more costly, offers even more features and abilities. 

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