Thoughts on reverb

by Jeremy "Jezar" Wakefield

The first thing you need to be aware of is that all reverb plugins are rubbish. That's right! All of them! It's just a fact I'm afraid. If you want to hear what real reverb is, take your stereo recording Minidisc into a church, put it in record, and then clap your hands a few times. Then yell out something. It's best if you do this when other people aren't around, because they might think you've gone mad and call the police. If going to a church isn't convenient, then try something like under a highway bridge late at night when it is quiet. Be aware you still might be mistaken for a lunatic and get arrested. Anyway, when you get the recording home, listen to it over and over so you can hear what's going on. You might even try emulating it using the settings on your favourite reverb plugin, but you won't get far. The hand-clap is probably the toughest test for a diffuse reverb sound. It has to be a real single-impulse hand-clap. Not that silly "crunch" from a drum machine.

If you don't have a recorder, don't worry. Just use your ears when you are next in an interesting reverberant environment. A real concert hall is amazing. Really make the time and put some serious effort into *listening*. Especially if you get there early on enough when the audience is shuffling about. Someone is bound to drop something with a bang, or crack open a can of Coke. Listen to how amazingly diffuse the reverberant sound is. Listen to the magical way it seems to be coming from all directions at the same time, listen to the gentle softness and subtlety with which it fades away. Now listen to your humble reverb plugin again. It's not even close is it?

Perhaps one of the best - and certainly most famous - of reverb devices is The Quantec Room Simulator. This device was first sold in 1982 - for a high price - and amazingly hasn't substantially changed since (more on this later). Quantec released another version that was controlled using an IBM PC, but no-one was interested in that (why would you want to leave a PC standing around in your studio just to adjust reverb settings? This was a thoroughly silly idea which nearly destroyed the company).

Quantec have now released a new Quantec Room Simulator, called The Yardstick. It uses the same 1982 reverb algorythm (in fact surprisingly, a slightly CUT DOWN version of it), and it comes in a much smaller box, and sadly has no analog inputs/outputs, just industry-standard AES digital connectors. "Buy your own A/D convertor box" they unashamedly say. "We're moving into an all-digital world".

If you want to hear what The Quantec Room simulator sounds like - and get some idea of the quality of top-end reverbs in general, then go to their web site at where you can download MP3 files showing what different room presets sound like. They have thoughtfully included the original dry test samples, so you can download those too, and see what results you can get out of your own reverb system. It is an interesting experiment.

The Quantec does a stunning job at simulating rooms, but is unfortunately not anywhere near as useful when mixing pop music as you might expect. That's why you often find a Quantec in studios that specialise in classical music, but less so in studios that do mainstream pop.

The problem is that you don't really want most pop music to sound like it was recorded in a particular "room" at all. When you mix, you want it to sound "spectacular" and "other-worldly", and this has much less to do with realism, and more to do with flexibility.

The mainstay of pretty much all top studios around the world is the "Lexicon". Of course you can buy budget reverbs made by Lexicon these days, but these aren't even close to their top-end units. For many years, the Lexicon 224X was the machine to die for, but this has been replaced by the cheaper and more powerful Lexiconn480L as the machine of choice.

I started playing with the Lexicon 480L in about 1986. It is still the premier machine. It is a source of mystery to me how a 1986 machine can still outperform everything else that's out there, still commanding such a high price. I can't remember offhand the technical specs of the engine in the Lexicon 480L, but perhaps it has DSP technology that is so top-end that it is above the line of quality that gets pulled into mainstream consumer electronics.

One thing that is for sure, is that it is certainly one of the most flexible reverb machines around. Not only do you have access to a wide range of adjustable parameters, but you can also configure the machine to be one, true-stereo machine, or instead, do what most people do, and configure it as two totally independant mono-in, stereo-out reverb units.

The large number of adjustable parameters on the Lexicon 480L mean that you can very much tailor a reverb sound for your particular song, and go beyond the "realistic" defaults for various acoustic spaces.

One of the problems with most reverb units - especially budget hardware ones, and nearly all VST/DirectX plugin units, is that they stick far too much to academic models of statistically perfect rooms.

Not only do such statistically perfect environments not exist in real life, but even if they did, you almost certainly would not want to record in them. A room with perfectly parallel, perfectly smooth walls? Erm.. No thanks! Real environments are filled with all kinds of interesting reflective surfaces and angles, and indeed objects, which leads to a fascinating "scattering" of the sound, in an almost chaotic way.

Another fundamental misunderstanding of academics (why don't they get their head of out math books and listen with their ears instead of tape measures and calculators?), is the assumption that reverb is based on two discrete components "Early reflections" and "Reverberant field". The "Early reflections" are normally just a bunch of taps off a delay line, supposedly representing the sound reflected for the first time from all the walls and ceiling. The "Reverberent field" is just a diffuse scrambling of the early reflections, with some kind of feedback to keep it going.

Anyone with so much as a whiff of common sense, who thinks about the problem for more than a few
milliseconds, can realise that this is nonsense. Even ones own ears will tell you that this is nonsense. Whilst people keep labouring away under the false assuption that these two elements are the key to reverb, then we will continue to have poor reverb units.

Both Lexicon and Quantec have proved by the existence of their products - by far the best reverb units in the world - that early reflections are just a myth brought about by clueless academics.

Quantecs argument against early reflections is simple and philosophical. A room is a just ONE signal processor of sound. It doesn't have the intellegence to seperate out the two concepts or even to care about whether a sound is direct or reflected. It just bounces and diffuses ALL sound, no matter what its source.

Lexicons argument against early reflections is a little more decriptive. They also argue that a room just reflects and diffuses sound, irrespective of source, but point out as well, that you could be hearing second or third generation reflections from the areas around you, before you even get the first reflection off the back wall. Reverb, Lexicon say, is an extremely complex reflection and diffusion pattern that BUILDS UP to a dense thickness from the moment you hear the original dry sound onwards. That's why the controls on a Lexicon are quite different to other reverb units, including important, but new, parameters like "spread" and "shape" to control how the reverb thickens and builds up before decaying.

After this, you realise that taking a simple pattern of dry echoes, and immediately splattering them into a dense reverb "field" will never give you the same depth of feeling and excitement that you get listening to the real evolution of reverberated sound in a concert hall. Real reverb doesn't just start, and fade, it changes - it travels - and *really* moves - you get a sense of that movement of sound in a real hall, and you feel a rush of excitement as it swirls around you.

The Chief Designer at Lexicon has said that Lexicon are now giving up simulating real rooms. They've done that successfully for years! :-)) Now, instead, they are analysing reverberant soundfields to figure out, what are the bits we really LIKE about reverb? Where does that excitement and sense of movement come from? What bits DON'T we need? Are there bits that are really just "mush" and don't contribute anything worthwhile sonically?

Of course - in your PC environment you are *greatly* limited by bandwidth, and that is also why plugins are so poor. The marketing people will want to sell as many plugins to as many people as possible, so there is a great deal of pressure to use up as little CPU as possible. Anyone who's written a bit of "C++" can write a Chorus or Delay plugin in their sleep, with little overhead on the PC. Reverb on the other hand is a real CPU hog. Some people are cheating, I'm sure of that. You simply cannot do the kind of calculations required in the amount of small CPU power that they have, so they are obviously making some assumptions and shortcuts. If anyone knows what tricks they are up to, I'd love to know. Please mail me if you have any details.

In the meantime, for most PC owners, I guess it's either a waiting game for the next generation of high-speed CPU's to come out, or to buy an expensive DSP card for your computer, or alternatively just to put up with the kind of fluttery rubbish that's out there at the moment.

Just don't try clapping your hands through it though.




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