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Spatializer PT3D

TDM Spatial Enhancement Plug-in By Paul White
Published September 1997

Paul White explores the far dimensions of space using this spatial enhancement plug‑in.

The Pro Tools plug‑in market is expanding at such a rate that in order to run all the different plug‑ins at the same time, you'd need an expansion chassis the length of a stretch limo, stuffed with DSP Farm cards. Plug‑ins perform a number of processing tasks, nominally divided into effects and processors, though I'm not quite sure which camp the Spatializer PT3D fits into. It's applied like a process, via a stereo insert in the Pro Tools environment, but the spatial enhancement treatment it provides is most definitely an effect.

Spatial enhancement software and hardware has been with us for many years now, the most notable players probably being Roland, with their very ambitious RSS system, and QSound. Spatializer build both hardware and software spatial enhancement devices, and their approach is more in line with that of QSound than that of Roland, in that their aim is to widen the stereo image rather than attempt to place sounds behind the listener using a conventional two‑speaker stereo monitoring system. The underlying process relies on spectral filtering and delay, applied to the signal being processed in such a way as to trick the human hearing system into believing that the sound is coming from the sides rather than from the front. Such systems also tend to include some form of crosstalk cancellation, because, in a normal loudspeaker listening environment, the left ear hears some of the output from the right‑hand speaker, and vice versa.

Spatializer have done a great job of making their PT3D very friendly.

To make stereo width enhancement work properly, a lot of real‑time processing needs to be done, but one thing the designer has to keep in mind is that the process must remain easy to control. In that respect, Spatializer have done a great job of making their PT3D very friendly. Once it's installed from floppy, all you have to do is insert it into the desired part of the signal path (for example, the master faders) and adjust three simple controls. Like most plug‑ins, the program is protected by having a limited number of installs: in this case, two. Before you format a drive, the PT3D needs to be de‑authorised in order to restore the install to the floppy disk. I feel insecure with such systems and find them incredibly irritating — if my drive needs reformatting, I have about half a day's work removing all the various installs from my drive, and if one gets missed, it's flushed down the drain with the rest of the data on disk.

The Interface

Spatializer PT3D appears as a fairly typical plug‑in window, though the Conservative Club colour scheme helps it stand out from the competition. Along the top of the window are the usual plug‑in buttons, but the majority of the window itself is taken up with metering. Conventional bargraph meters show the output level, but separate meters are included to show the sum and difference signals between the two channels. A further meter monitors spatial impression by simultaneously showing left and right deflection from a central mono point. Impressive though the metering is, it's not just for show — for example, if the Sum meter constantly reads a low value, there's a likelihood that mono compatibility will be compromised.

The first slider control simply sets the gain of the processor — some settings can cause gain increases, so it may be necessary to adjust the Gain control to prevent this. Space, as you might expect, sets the amount of spatial enhancement: the higher the setting, the wider the sound. Finally, Center adds a mono summed version of the signal back into the mix. The widest mixes are obtained when this control is set at zero but, on some material, sounds mixed dead centre may seem to fall back in the mix. Adding more Center can restore the natural balance of the mix without unduly diluting the stereo‑widening process.

In Use

The process works fine on both whole mixes and submixes, although, to maintain maximum contrast, I'd tend to use it just on submixes so as to push some elements of the mix out beyond others. For example, delay or reverb effects, backing vocals, and abstract synth parts can be pushed right out to the sides; unlike conventional ghetto‑blaster stereo wideners, which work on phase only, Spatializer's process genuinely creates the impression that parts of the mix have moved forward and wrapped around the sides of the listening environment. In fact, the effect is very seductive: when you bypass it, the sense of loss is similar to that experienced when you switch an exciter out of circuit, or switch a stereo signal to mono.

A potential problem with all stereo enhancers is that they can compromise both tonal balance and mono compatibility. On the mono‑compatibility issue, I've always felt that as real life isn't mono‑compatible, nobody should expect recorded material to be either. Provided that the side effects of listening in mono are within acceptable limits, why worry too much? As it stands, the comprehensive metering provided within this plug‑in provides a good indication of potential mono compatibility problems, though I feel a mono test button could have been added to the plug‑in button menu to allow the user a quick and easy means of assessing the situation.


Tonally, the Spatializer PT3D is surprisingly benign, with no obvious loss of bass end or punch. Obviously there are some EQ changes to create the spatial illusion, but these are quite natural‑sounding and create the impression of certain sounds moving closer, rather than seeming to be changes of level or tone. Apparently, most of the processing occurs between around 400Hz and 5kHz, and the manual suggests that equalising at 500Hz and 2kHz can provide interesting results. This particular process is designed to be compatible with Dolby Pro‑Logic — though, as the manual points out, it isn't designed as a substitute for that process, and mono compatibility is also very reasonable in most cases.

Personally, I like 3D enhancement effects, providing they're used carefully, and I feel they can add a sense of intimacy and dimension to a mix that conventional effects can't replicate. Of the 3D audio packages I've tried, it's probably fair to say that Spatializer PT3D is one of the most straightforward to use, and the auditory illusion it produces compares very favourably with competing systems.


  • Simple user interface with good metering.
  • Impressive degree of width and depth enhancement.


  • Compatible with Pro Tools TDM systems only.


A straightforward and very effective spatial enhancer capable of very convincing results.