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May 2005

Waves IR-1 Convolution Reverb
Powerful controls and flexibilty
Review by Glenn Bucci

Most reverbs in hardware units or plug-ins, are a synthesis approximation of what halls, plates, and rooms are. However only the high-end units can come close to sounding like real acoustic rooms. With convolution reverb though, we are able to get realistic reverb at a very low price.

Convolution reverbs use impulse responses of real acoustic spaces. The impulse response is captured by generating a known signal in the required environment and recording the result. The convolution process effectively cross-multiple's the impulse response with the dry audio so that the end result is that the source audio sounds as though it was originally recorded in the real space. This apparently simple procedure is, of course, very complex in practice! If the reverb tail takes ten seconds to die away, the convolution process requires that for each individual sample in the source signal (the one we want to add reverb to), we have to replay a string of half a million samples of reverberation, with each sample suitably modified in level in accordance with the amplitude of the source audio signal. Changing the gain of digital signals requires a multiplication process for each and every sample, and the convolution process gets even more complicated when you cons ider that this stream of modified reverberation samples then has to be added to the all the other strings of reverberation generated by all the proceeding (and following) audio samples, as well as to the audio samples themselves. And that is one hell of a lot of multiplications and additions! Fortunately, this 'multiplication and add' process is a common requirement in digital signal processing and modern DSP chips (and even multi-functional computer processors) can perform them at huge speed. It requires a lot of calculations, but the process itself is very simple -- and a lot less demanding than having to synthesize sufficient individual reflections and decay tails to simulate natural reverb. In effect, the original room impulse response already incorporates all the hard work

This takes us to the Waves IR-1 convolution reverb. This software is available in TDM and Native for Windows 2000, XP as well as Mac OS X users. In using any convolution software, the impulses use a lot of processing which takes a lot of CPU usage. The IR-1 can be used at 44 kHz - 96 kHz, and naturally it consumes more CPU at the higher sampling rates. They recommend having at least a Pent III or G4 with 512 ram. I would recommend having a Pent IV or G5 with a minimum of 1 gig of ram to run it smoothly.

Waves worked with Professor Angelo Farina from Italy who developed new measurement techniques, which were done at 96 kHz, and set of 360 degree surround measurements for some very amazing impulses. The software comes with two CD-ROMs with over 60 room types from auditoriums, theaters, small rooms, medium halls, churches, recording studios, outdoors, opera houses, amphitheaters, clubs, stairwells, car interiors, and stadiums. Plus there are 60 different hardware device presets as well. The IR-1 is available itĚs full and a Light version. The LE uses all the same impulses, cost less, but has limited controls compared to the full version.

I found the IR-1 to be very straight forward and easy to use. The screen display is very neat and organized and pleasant to the eyes. They have recently come out with version 2 which includes: Ý

  • New Tools to capture your own impulse responses. Capture the sound of your favorite acoustic spaces and hardware devices.
  • New Convolution Start Control to trim the beginning of an impulse response to eliminate unwanted predelay.
  • New ER (Early Reflections) Buildup Control allows for adjusting the buildup slope of the early reflections to control their attack sound, from crisp to smooth.
  • New Dry Gain Mode gives more control over the sound by letting you adjust the wet and dry signal gains separately in addition to the option of using the traditional dry/wet control.
  • New Extensive Library of Improved Impulse Response Samples with Different Micing Options.
  • New Dynamic Preset Handling: Adding or removing presets is now easier, with the preset menu reflecting the impulse response samples contained in the presets folder.

The IR-1 offers more controls than most convolution software programs currently available on the market. They include the following;

  • Reverb Time RT60: Unlike existing products, IR-1 V2 uses unique impulse response (IR) manipulation techniques to allow shortening and lengthening (times 4) of the reverb time while maintaining acoustic coherence and preserving the natural envelope and frequency content.
  • Size: Controls the room size by applying acoustic modeling to the impulse response sample, adjusting the early reflections to make the space smaller or larger while maintaining its signature.
  • Reverb Decay Envelope: A graph-based multiple breakpoint envelope allows unlimited options for reshaping the reverbĚs decay behavior.
  • Density: makes the space sound clearer or denser by applying modeling methods to alter the reflections, resonance, and inherent randomness of the impulse response sample.
  • Reso (Resonance): analyzes the frequency response of the impulse response sample and derives the room modes, allowing acoustically-based control of the modal timbre.
  • Decorrelation: While not a classic reverb control, decorrelation allows greater control of the reverberationĚs stereo spaciousness.
  • ER/Tail/Direct Independent Control: IR-1 V2 analyzes the impulse response sample to find the early reflection and reverb tail (ER/Tail) boundary markers, which then allows you to alter these characteristics using the classic controls of gain and pre-delay for each portion.
  • Damping:' proportional to the reverb time, this control applies innovative filtering methods to control the impulse response sample's low, mid, and high frequencies separately.
  • 4-Band Paragraphic EQ: Controls the reverbĚs color using a 4 band paragraphic equalizer based on our renowned Renaissance EQ plug-in.
  • CPU Usage Control: Special Efficient-Stereo components requiring less processing power; A "low CPU" mode utilizing intelligent algorithms that require less CPU usage while preserving high sound quality and definition.
  • Convolution Length Control: This allows control over the length of the actual real-time convolution. Therefore the CPU load can be reduced if desired by using a shorter convolution length while maintaining the RT60.
In using their impulses, I found them to be smooth, very clean and detailed. The vocals or instruments being used with the Wave impulses sounds like they were recorded in the venues. With synthesize reverb units, a lot of times it sounds like your adding a reverb on top of the signal. But with the Waves impulses (as well as many third-party's impulses) you get the impression that the signal was recorded in the room you chose. Wave's impulses generally sound very good with its presets. Being able to adjust early reflections, tails, size, damping, changing the EQ and other features makes it very flexible. If you alter the controls modestly, you can get different character and size while still retaining the great sound.

On the downside, every time you make a change to one of the knobs, it takes the program about a second to recalculate the reverb. The left side of the screen shows the original preset setting values, and to the right the current settings values. This is a helpful aid in situations where you made changes, and you see how different the settings are from the default setting. Like most Waves plug ins, there is an A/B switch which is very handy. There is also a low CPU button that you can choose if you start running out of CPU power. I noticed very little difference between the two settings. It can reduce your CPU level by 20-40% from the full setting.

In a session I added a plate reverb to a lead vocal track. I was able to adjust the plate so it had (it took less than 5 minutes) a sound my client was happy with. The EQ allowed the high end to have a little crisper sound without adding bad artifacts. One of the studio rooms made my bass guitar just has a little more life without having any washy reverb sound. Many of the other convolution software lack this flexibility of the IR-1 and force you to work with limited changes within a preset. The IR-1 cost more, but it is still thousands less than the high end hardware reverb units, while still giving you similar flexibility.

Since most convolution reverbs sound similar when fed with the same impulse responses, the big question is, is the higher cost for the Waves IR-1 really worth it? The answer depends on what your needs are. There are many convolution plug ins out there today from the free SIR with very limited controls, to the inexpensive Prosoniq Ray verb, and Voxengo Pristine Space which offer a little more flexibility. If you have Logic 6.3 or higher, it comes with their Space Designer which also has more controls than SIR, and works very well. Once you have any of these software packages, you can go to many web sites to download impulses for free.

If you want the high end reverb sounds, and are content with limited controls, I would recommend getting one of the above mentioned software programs. However if you want more control and flexibility, I easily can recommend the Waves IR-1. On the Waves web site, there are additional impulses you can download as well giving you more venues to choose from. However you cannot download any of the Waves impulses unless you have an IR-1. It should be noted that not all impulses are done with great care and skill that Waves has taken. Many just use the balloon method, which can reflect in reverbs that don't have the same intimate detailed sound that Waves offers with their impulses. Thankfully you can also import third party wave impulses in WAV form to the IR-1 as well.

Before I reviewed the IR-1, my feeling was most of us just need one of the cheaper plug-ins above, with convolution impulses available online. However after comparing the IR-1 to the other packages, I feel the additional flexibility justifies the higher price. Then when you add the high end impulses from Waves, it makes it impossible for me to resist keeping it. With other software, you are limited to the presets with limited control. This can give you great sounding reverb that is either too big or too small for your session, which the wet/dry control will not fix. So if you want high end impulses and great flexilbity, I recommend looking closely at the Waves IR-1. I had no choice but to buy this amazing reverb.

A special thanks to Hugh Robjohns from Sound on Sound for his assistance on explaining the convolution process.

For more information visit www.waves.com


Glenn Bucci is a musician and received the same degree in recording as Rupert Neve, which Rupert calls QBE: Qualified by Experience. He owns Revelation Sound Studio, where he engineers and produces for clients and works on his own original blues/ jazz material.

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