Posted by John Howard on Nov 26, 2011 | 1 comment

The need for audio engineers to make tracks sound as if they are coming from various types of acoustical environments is as old as audio production itself, and has only intensified with the use of audio in film. Of course, when shooting for realism, the initial (and still the best) solution was to actually record the sounds in those environments – concert halls, theaters, living rooms, vehicles, etc. Then studio engineers like Bill Putnam Sr. and the like thought, “Hey, we have this facility with all kinds of rooms – why don’t we play back an audio signal miked in a dry room (one with little reverberation) into a wetter (more reverberant) room with a loudspeaker and mic the results?” And thus, the art of applying additional reverberation to tracks was born. The process has undergone a great deal of mutation since then, with the creation of reverb devices utilizing anything from metal plates, springs, a series electronic delay lines, all the way to modern digital equipment with powerful IC’s.

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Today’s digital reverb processors generally fall into one of two categories in regards to how they produce their effects: algorithm-based and convolution-based. The former uses proprietary algorithms based on various mathematical formulas to simulate the acoustics of different types of rooms. Once a manufacturer has an algorithm perfected they create many presets based on that algorithm for their product, which will include anywhere from several to many user-addressable parameters by which the lucky owner can change the variables within the formulas in a user-friendly way. Reverb generation based on the convolution technique uses Impulse Responses created from recorded samples taken from actual acoustic spaces to essentially infuse the acoustical properties of those spaces into the signal running through the processor. Both reverb types are very viable and used every day by audio professionals the world over. They both have their own sound, and I use both types, choosing the one that will be the most flattering for a track given the goals of the piece.

Because of the intense number-crunching necessary, convolution reverbs used to only be available as (very expensive) hardware units, but as the speed of modern personal computers has increased and the code refined, the technology has found another home in plugins that run full-quality convolution reverbs on a computer’s CPU. Audio Ease’s Altiverb 6, one of the first convolution reverb plugins made available for personal computers, is just such a processor. It’s robust convolution engine, intuitive user interface, and extensive, ever-evolving library of free impulse responses of spaces (and gear) from all over the world make it, in my opinion, the poster child for convolution reverb plugins. (For more on the history of reverb techniques, devices, and the people who pioneered them, check out this article from Universal Audio: The Basics of Reverb )

Ease of Use

Installation was fairly straight-forward. Though I did have to email the manufacturer to figure out what I was doing wrong at one point, I think it had more to do with the fact that I got the license through MFM and I was entering incorrect information during the authorization process. The response was kind and prompt and got things ironed out so I could proceed with authorizing the product. Speaking of, the software offers two methods for the task: challenge/response or iLok authorization. It’s nice that the folks at Audio Ease realize that different people have different preferences.

Altiverb 6 – actually now 6.3.3 via free updates – has so much going on under the hood, but it is easy to understand and use thanks to its innovative displays, intelligent use of tabs that reduce a number of options (that would otherwise use up most of your screen) to a modest footprint, and a well-organized layout that is informative without being overwhelming.

The IR (impulse response) browser is located in the main display window (top center) and is accessed by clicking on the IR browser tab just above it. It organizes all installed IR’s into categories, the names of the spaces or pieces of gear, and then lists the actual IR names for each. As most spaces were sampled several different ways, helpful information about distance and the type of mics used is part of the IR names. The other two tabs here are for displaying the IR in different ways. Additional information about the space or equipment in the Info window to the right. Here you can see pictures of the space, take a 360-degree look at it, read more about the location, etc.

The bottom-center portion displays four different groups of parameters: Damping & Gains, Stage Positions, Equalize, and Options. This makes it easy to pop back and forth to different settings you need without running your mouse and eyes all over the screen for them. I have to give Audio Ease further props for the innovative way that Stage Position allows you to place the source position (represented by loudspeaker icons) anywhere in the virtual space and record your movements as automation/animation data as you drag them around. There’s a lot more going on behind the scenes here than simply changing the balance between the source audio and the effect. There are proprietary algorithms at work that are modeling room characteristics and somehow putting the IR through this sort of like a post filter. The result sounds much more realistic! Along with the automation capabilities, it suddenly becomes very easy to realistically emulate, for instance, the way footsteps in an empty warehouse contain more reverb when the subject is farther away and less as they walk closer to the camera – if you’re unlucky enough not to be able to capture the sound on location for some reason. This is useful for music production as well. Recently, I used a music box type patch from one of my VST instruments on a rock song – threw it into a cathedral using Altiverb and automated it to sound closer during breakdowns and farther away during the lead vocals. It was awesome!

The remainder of the display contains more standard fare, with the exception of the buttons for various test sounds that will play through the current settings. This is a thoughtful, unique feature that those with less powerful machines will certainly appreciate since the intense math involved in all of this can make real-time adjustments a bit sluggish on these systems.

Depth of Options

Historically, most convolution reverbs lacked much control – sort of a play-your-sound-through-this-space-and-if-you-don’t-like-it-pick-a-different-space kind of thing with few parameters to play with. More recently, manufacturers have put out products offering more parameters, but many sound less than authentic. I feel like this is because these processes are being added to the sound of the IR rather than manipulating the IR itself. I’m not a programmer, but this is what it sounds like is going on. At any rate, the geniuses at Audio Ease have somehow managed to do it right, whether through manipulation of the IR, pre/post processing, or a combination. Altiverb 6 has a wealth of settings tweak heads will love and the results sound fantastic and realistic if the settings are kept in a reasonable range – yet I love the fact that they allow settings to be cranked to unreasonable heights and depths for special effects when desired.

Altiverb Regular includes mono and stereo functionality and supports VST, RTAS, and Audio Suite plugin formats on Windows and MAS, AU, RTAS, and Audio Suite formats on Mac OS X. The more expensive Altiverb XL adds surround functionality, ProTools’ TDM plugin format support, and support for sample rates in the host-based formats up to 384 kHz.

The quality and usefulness of any convolution reverb ultimately comes down to the impulse responses. Altiverb’s IR’s are great – and widely varied, covering anything from cathedrals, concert halls, chamber halls, monasteries, smaller music rooms, tracking rooms from various studios, any room in a house, stairwells, the inside of vehicles, airplanes, tombs, bus tunnels, and tiny spaces like the inside of a can, toilet, or vacuum hose, to classic effects processors like the Roland Space Echo RE-201 tape delay, the Lexicon 224 XL, Sony SDR 1000+, etc. What’s more, the IR library is constantly being expanded, and the IR sets are available to download from their website for free, assuming you are a registered user. Altiverb will even allow you to add third-party IR’s for use with its robust convolution engine.

In order to give us a better idea of what the IR’s and settings are actually doing, Altiverb 6 offers two types of graphic representations: waveform and waterfall. Both are accessed by clicking on the appropriate tab above the top-center display window. Waveform is basically a 2D look at time (X) and amplitude (Y) for each microphone used in the current setup. This is especially useful for zooming in and seeing how much delay is present between the left and right mics when sounds originate from the other side, giving you an idea of how “wide” the effect will sound. I personally really enjoy the waterfall display. It adds a third dimension (Z) to represent frequency. This enables me to see exactly how my settings are changing the reverb time of various frequencies, which gives me a much better idea of how things will sound. The interface also lets me rotate and zoom in/out on the graph so I can really dig in if I want. It is educational, especially for the less experienced, to have this kind of visual feedback available to essentially show you what you’re hearing. You can learn a lot about how the size of a room changes the room’s resonances and how EQ and damping will change the perceived length of the reverb at certain frequencies. Great fun!

Okay, so we have these amazing IR’s and an easy way to see what they’re doing to our audio. Now, what tools do we have to actually manipulate the sound. In a word, plenty. Like I mentioned at the top of this section, most convolution reverbs don’t offer much in this department. So I was very excited to see what I could do with all of Altiverb’s settings!

Reverb Time (top-left) manipulates the IR to shorten or lengthen the decay of the reverb. Size is an innovative settings that actually alters the room resonances, or more correctly, its modes. The dimensions of a room cause the bouncing of sound waves to not only reinforce certain frequencies, they also attenuate certain other frequencies. So Size allows much more realistic alterations to the perceived volume of air in a room than simply adjusting decay time. It also provides ample opportunity to mess with the listener’s head a bit by creating a room with a size setting that’s contrary to the overall characteristics of the IR – so you can imbue your audio with certain properties of a large and small space simultaneously. Also in this section of the layout is the Reverse button which, as you might expect reverses the reverb so you can create this popular special effect. This is especially useful for sound design purposes in film and music production alike.

Now let’s focus on Altiverb 6’s bottom-center section. Damping and Gains offers settings to tune the timbre and loudness of the room’s IR. Three-band damping lets alter the degree of absorption or reflection of the room for three customizable frequency bands labeled low, mid, and hi. These settings seem so simple, but are extremely useful for altering the tonal character of the reverb itself which can completely change the mood of a track. The gains portion has settings to adjust volume and other properties of the direct (source) sound, the early reflections (initial echoes that come nearby boundaries), and the tail (the long diffuse end of the reverb). There are many applications for these settings. Obviously, you can use them to further alter the character of the room your are simulating. But what if the track already has some audible reverb present in the raw recording? More specifically, what happens when the early reflections in the recording combine with the early reflections of the IR in Altiverb? It could be fine… or it could be the audio equivalent to mud! Well, simply turn down the gain of the early reflections here to solve that problem. Then, if there is a gap between the early reflections in the recording and the tail from Altiverb, play with the Tail Delay settings to adjust the onset of the tail. If you can’t blend the recording’s reverb with Altiverb’s effect, try an IR of a space that sounds more similar to that in which the original recording took place. Using these settings, I’ve been able to successfully trick the listener into perceiving that a track was performed in a concert hall when, in fact, we recorded it in a much smaller room designed to seat around 200 people.

I think I already mentioned the power and usefulness of the Stage Position feature above. All I can say is “Wow!”. What a thoughtful and innovative way to control the perceived distance of your source track! Just grab the speaker icon and move it around – you’ll figure out how to use this feature as soon as you hear the results. For stereo IR’s two speaker icons are displayed. These can be moved independently or linked to automatically mirror each other when only one icon is moved. By engaging Stage Positions, you are controlling the timing and loudness of the direct sound. As such, the Direct Gain and Mute Direct settings become unavailable.

Clicking on the Equalize button brings up several knobs for altering the volume of four different frequency bands and a multicolor graph above them representing the changes made to each band. Bass and treble frequencies are set for you and cannot be changed, whereas the two mid-frequency bands can have their center frequency and Q (band width) set by the user. The larger knobs are for adjusting the volume of each band. The equalizer works on the wet (effect) signal only, so you’ll probably want to make any necessary EQ changes to the dry sound prior to Altiverb in the signal chain for the most natural sounding results.

The Options button reveals settings that are useful for tweaking how the plugin hits your CPU, which many users will appreciate, no doubt.

Just to the right of this section of the plugin window you’ll see several controls for Input and Output volumes and the Wet/Dry Mix. Lower the Input setting if you experience a volume build-up from a long reverb tail that overloads a gain stage somewhere in the plugin and create distortion. The Output setting is useful for tailoring the overall volume of the plugin. The Mix knob adjusts the ratio of the sound of the original track to the signal Altiverb is generating. Clicking on the Mute Direct button below this knob completely silences the original signal. This makes it possible to listen to only the sound of your track played in that space without a re-infusion of the original signal. This is the recommended way of setting Altiverb in an effects send method (rather than as a channel insert).

Altiverb 6 also offers robust automation and preset management. The complete state of Altiverb can be saved in a Global Preset, or in a Automation Preset. Global Presets are presets that are available across sessions (songs / projects). The factory presets are also available in this menu, and are nicely organized into categories. Automation Presets are presets that are saved into the session. They are private to a single instance of Alltiverb and can be recalled via snapshot style automation. Then, of course, if your host program supports real-time automation (animation) of parameters, this opens up a very powerful means of morphing the perception of subject or instrument in the space along your project’s timeline!

Performance

As I have already alluded to several times, the quality of Altiverb 6’s convolution is stellar. With default settings in the Options section, Altiverb responds to parameter changes in real-time which, though slightly sluggish at times, is huge for a convolution reverb plugin! Moreover, it did so without any audible ‘zippering’ or ‘popping’ artifacts. As if this wasn’t difficult enough to achieve, more recent updates to the plugin have yielded way lower CPU usage than previous versions! The result is a surprisingly low CPU hit, considering a convolution reverb generating a long tail at full-quality is one of the most intense audio processes your computer will ever see. Further, features in the bottom-center section are deactivated by default to conserve CPU cycles – only turn on the features you need for that instance of Altiverb. Load times are a bit slow upon the first instantiation into a project – about 10 sec. – but the sound is worth the wait and it gives me a chance to respond to a text while I wait.  This may be different when using different host programs and operating systems.

Value

Altiverb’s price tag isn’t the lowest on the market. It just sounds the best and offers more options for shaping its effects of any convolution reverb plugin I’ve ever seen. Essentially, it offers me as much as I would get out of very expensive hardware units – more, actually, because I can run several of them at once. So, in my opinion, it’s worth it! Units with a 5-figure price tag may offer certain advantages, but for my money you just can’t beat Altiverb.

Final Comments

As if you can’t already tell, I’m in love Altiverb 6! From the beautifully recorded IR’s to the extensive manipulation options it offers, the plugin shows its maturity and is simply a class act all the way around. Anyone out there looking for a super realistic-sounding means of putting your audio into various spaces or through different types of classic effects processors that aren’t available any more (for a reasonable cost anyway) should seriously give this plugin a fair shot at impressing them. My guess is it will!

John Howard

John Howard has been perfecting sound as an audio engineer for over 10 years. When he's not reviewing gear and software for Microfilmmaker Magazine, he's in the studio recording vocalists and bands, as well as doing post for TV shows and films, through his audio post/recording company, Oakwood Sound Design.