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Edit Review: Audio Ease Altiverb 5

Jan 1, 2007 12:00 PM, Reviewer: Gary Eskow

Convolution reverb app brings ambience and depth to the audio mix.

Of the many exciting advancements digital audio has given us in the last decade or so, convolution reverb is, in my book, near the top of the list. Convolution reverbs are the latest — and perhaps the last — step in the development of tools that let the engineer create a large, natural-sounding environment for placing detailed and highly-localized audio files.

But what exactly is convolution reverb? According to the venerable Mr. Webster, to convolve a pair of items is to roll them together. Fair enough; convolution reverb is the “rolling together” of source audio and the sample of a reverb. To create the sample itself, engineers take an impulse — a starter pistol or sine wave sweep, for example — and record it in a reverberant space. Afterwards, the impulse is surgically removed from the resultant audio file, and you're left with only the ambience of the environment itself (the Grand Canyon is a classic example). On top of that, the results live up to the concept, whether you're using a hardware convolution unit such as the Sony DRE-S777 or the Yamaha SREV1 (both of which cost upwards of $10,000), or software plug-ins such as Audio Ease Altiverb. Long a Mac plug-in, the software's recent release is a PC version of Altiverb 5 that features competitive pricing at $595. (Altiverb 6 was released this month.) Let's take a look at Altiverb, how it sizes up to the competition, and the applicability of convolution reverb to your audio post work.

Altiverb's main competition, the IR-1 from Waves (Waves offers several different convolution reverbs — visit www.waves.com for a complete breakdown) employs a more traditional interface, with sliders' multiple-point envelope editing. Experienced engineers and newbies who are willing to put in some time will be able to get excellent results from the IR-1. But most users will find Altiverb's GUI more appealing and user-friendly. All of Altiverb's main features, including the stage positioning, tail length, and early reflection controls are accessible from the main screen. A well laid-out explanation of Altiverb's feature set can be accessed by clicking the following link: audioease.com/Pages/Altiverb/Help. So, rather than recite all its features in detail, let's move on with our general inquiry into convolution reverb, and how it works.

Convolution reverbs combine impulse responses — the “sound” of the environment itself — with other variable parameters (settings for eq, reverb time, and the size of the space) into presets, and Altiverb is no exception. In addition to the presets that ship with the plug-in, you can easily save your own presets. If you're not familiar with the basic principles of how to use reverb, you'll definitely want to put some time into learning how to get the most out of equalization and damping.

Music engineers know, for example, that the further sound travels, the more high-end information is lost. If you're using samples to create an orchestral mock-up in a concert hall, and the snare drum is the instrument sitting furthest back on-stage, it would make sense to roll off some of the high-frequency content in order to move that instrument to the rear. The same principle holds true if you're posting audio from a mysterious scene shot on a dark street late at night. Sure, those screeching tires have high-frequency data contained in their sound, but where do you want them coming from? If the car's image is in your face, you'll equalize its sound to emphasize the upper frequencies that are most present at close range. But if it's somewhere off in the distance? Right, you roll off of a bit of the highs.

Spend a little time playing with damping, and you'll soon find yourself capable of localizing information with precision in Altiverb. If you know that multiple video clips have been shot in the same locale, once you have settings that maximize your use of the stereo or surround image, save them as a preset of your own. (Note: The Mac version of Altiverb has long included 5.1 reverb, but the PC version does not at this time. Waves' L-1 is a stereo-only plug-in, and its surround reverb, the IR-360, is a seperate application.)

One cool trick is to use multiple instantiations of Altiverb to help you create a stereo image. This may also work with surround imaging, but I can't say for sure, because I was using Altiverb on a PC. Audio Ease says that surround reverb works exactly as the stereo version, with the simple addition of two more microphone, or output, locations. Audio Ease also says that a reasonably fast computer can handle up to 28 or so instantiations of Altiverb, as long as you're using most of them to simply assist you in your imaging (reverb is extremely CPU intensive).

Let's say you're dealing with a mono audio file — the very manly protagonist's hideously screeching mother-in-law, for example. Click on the Stage Positions button, and you'll see a single speaker icon, which you can drag around the “stage” in realtime and eventually designate a location for the sound. Perhaps you've recorded a stereo voice over a clip that's going to be processed to sound like the announcer calling the Belmont Stakes race. If you feed this signal through a stereo impulse response — meaning that two speakers fed the original impulse into a pair of microphones (rather than a single one), which in turn fed this data into two channels of a recorder — you will be able to click on a pair of speakers and move this audio wherever you want within the stereo field. It's a great feature. However, it would be nice to be able to automate stereo imaging, but that didn't seem possible. Depending on the number of inserts you've used and the power of your CPU, you can then set up a main reverb (certainly necessary for a music mix, possibly needed in an audio post session) and perhaps a second reverb for certain instruments or sub-groups.

Although convolution reverbs have an important role to play in music mixes, their value is even greater in audio post. For the most part, music engineers still rely on reverb — along with delays and eq — to help bring ambience and depth to a mix. The really wacky stuff comes into play more during sound-design work, and when an audio post engineer is trying to create unusual or even unreal sounds.

Check out some of the more exotic IRs on the Audio Ease website and you'll see what I mean; the company has sampled metal chambers, flower pots, and even the inside of a washing machine. Placing dialog or ambient material in one of these spaces will start to give you an idea of the unearthly dimensions that convolution can help you create. You can even take a couple of speakers and some microphones out into the field and create responses that cater to your specific needs. Of course, sometimes the most satisfying results come the most easily; while mixing a demo last week that featured the superb vocals of my old friend, singer-songwriter Jon Pousette-Dart, I simply strapped the IR that Audio Ease sampled from pioneer synthesist and composer Wendy Carlos' old EMT 140 plate reverb across his tracks, and the effect was stunning.

So, you want to buy a plug-in convolution reverb. Which will it be: Altiverb or the IR-1? Either way, you're in good shape, and if you already own a bunch of other Waves plug-ins, the award winning IR-1 may be a logical choice. On the other hand, Altiverb is cheaper, its IRs are just as creamy, and over time, my guess is that there will be more of them; audio post users will be happy to know that a gaggle of new effect-type reverb chambers — including, but not limited to, the ones we discussed earlier — are now on Audio Ease's site. Altiverb also offers the stereo positioner, a feature that is not included in the IR-1.

And it gets better: If you're interested in sticking your toe into the convolution stream, you can start out by downloading SIR, a convolution reverb that's absolutely free (www.kvraudio.com/get/736.html). SIR might be all you need, but if you must minimize latency and gain maximal control over the parameters of your convolution reverb, you'll probably move on to one of the plug-ins we've discussed in this article. Either way, if you're ready to step up and deliver the next level of professionalism to your clients, convolution reverbs should be integrated into your workflow.

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bottomline

Company: Audio Ease
audioease.com

Products: Altiverb 5

Assets: Handles up to about 28 instantiations, users can save their own presets.

Caveats: No ability to automate stereo imaging.

Demographic: Audio post editors who want to deliver the next level of professionalism to clients.

PRICE: $595

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© 2008 Penton Media, Inc.