Altiverb, introduced about three years ago, was the first sampled reverb plug-in to become widely available – but you needed Digital Performer to run it. Now it’s available in all the popular formats. Altiverb doesn’t produce reverb itself. Instead, its convolution algorithm combines a dry input signal with an impulse response measurement that was originally recorded in a real acoustic environment – creating a much more realistic reverb effect than standard digital reverberation processors.
The controls couldn’t simpler. Choose an impulse response using the pop-up selector in the middle of the window. The large knob at the left adjusts the length of the decay by applying an exponentially decaying envelope to the impulse response – so you can only shorten the tail. Two small knobs adjust the wet/dry balance between the effected and original signals. A third, marked pre-delay, delays the wet or dry signals in relation to each other to create special effects or to improve stereo imaging.
When selecting a response, a picture appears at the right of the window. Buttons display photos showing how the impulse response was recorded. A layout diagram explains how the speakers and mics were set up. Running audio through Altiverb produces the same effect as if the source sound was played back through these speakers in this acoustic space and then re-recorded using these microphones.
Detailed instructions are included on how to make your own impulse responses, and you can use these to capture ‘acoustic signatures’ of any non-time-variant systems – from favourite room or hall to your favourite outboard gear, microphones or guitar amplifiers.
Altiverb is compatible with Pro Tools HD Systems and can be used in high sample-rate sessions – even though it currently uses 48KHz IRs. Altiverb downsamples incoming signals at higher sample-rates (such as 96KHz) to 48KHz, adds the reverb sound, then upsamples the output back to the higher sample-rate used in the session. This is reasonable, as it minimizes the processing load. HTDM plug-ins use the Mac’s processor – not Pro Tools DSP chips. This is good for Pro Tools users who never have enough DSP, but you’ll need a fast Mac. As the manual puts it, “Altiverb taxes the processor severely” – and it does!
Compared with Emagic’s Space Designer, Altiverb offers better ‘classic’ reverbs, while Space Designer has more special effects. The main competition for Altiverb is the new Waves IR-1 sampling reverb. This has an even more comprehensive IR library than Altiverb, but costs significantly more. The IR-1 offers more-detailed control of the reverberation parameters and uses state-of-the-art 96KHz/32-bit impulse responses, but lacks Altiverb’s appealing simplicity and places a much heavier load on a Mac’s processors. If you have to make a choice, Altiverb fills the middle ground nicely.