- Aug 4, 2011
My Immersion Into IAP
I’ve been listening to stereo since the ’70s, and was not a fan of quad or the like, what with sound bouncing around rather than creating a cohesive surround space. If one wants to hear a good reason quad deservedly died, pick up the Chicago (CTA) DVD from Rhino.
Fast forward to my job at Dolby Labs where in the mid '80s I was working on launching Pro Logic into the nascent home theater scene. Movies on VHS and laserdisc came alive. Then RCA and Delos began creating surround CDs for Pro Logic playback. Interesting, but ultimately not to my liking; too much sound forced into center, narrowing the stereo effect, and the mono rears collapsed the space further. Dr. Greisinger and Jim Fosgate had long ago figured out how to create a compelling surround effect from stereo music, but it wasn’t until 1999 with Fosgate’s totally re-imagined process that I (and Dolby) could see it as a viable surround music solution for consumers. Pro Logic II and its 7.1 extension, PLIIx, are the result and there’s no more ubiquitous surround decoder extant.
Even though I am quite proud of PLIIx, and use it every day for music listening, there are times when it errs or “does too much” so I switch to direct stereo playback. The purity is undeniable and it leaves me searching for a surround processor that strikes a different balance in the “cost/benefit” equation, if you will, one that better preserves the pristine attributes of the stereo source yet still imparts a larger surround space.
Thanks to the generosity of Christof Faller, owner of Illusonic, I was able to audition his new Immersive Audio Processor (IAP) in the confines of my home theater. The IAP supports up to a “15.1” configuration, with 9 main speakers and 6 height speakers, in almost any combination. In my case, with “only” a 7.1 system, I chose the traditional 7.1 configuration. Thus, I am not able to report on the full IAP experience, but based on what I found, I’m confident the addition of height speakers would only further enhance the result.
The IAP can accept analog or digital PCM sources, up to 7.1 via analog or HDMI. There is no codec support, so all sources must be provided as PCM. Not a problem for my Oppo BDP-93.
Connecting the IAP to a computer via USB enables firmware updates and speaker setup. The firmware update process is the easiest I have encountered, easier than the world famous Oppo BD players, where even with automatic Internet download, you still have to click a few buttons and reboot, and perhaps reload some settings. Here, you double click the file, it loads in seconds, and you’re done. All settings are retained. Well done!
The speaker setup tool is similarly slick, but thus far only works on a MAC. I was easily able to enter all the settings from my SSP-800 (level, crossover frequency/slope, delay, PEQ) into the IAP. I had to translate distance to delay, but a future version will allow a choice of distance and units. When finished, I ran electrical EQ sweeps of each channel with REW to see if things matched the SSP-800, and I did have to make one minor change to the Q of one of the EQ bands, and I also needed to select “Order 2 Alt” for the crossover slope as that perfectly matched the 12 dB/octave Butterworth high-pass filter type used by the SSP-800. With the EQ and gain plots now perfectly superimposed, I was ready to listen, explore, and A/B against my current processor for reference.
The IAP is classified as a surround upmixer in that its primary mode of operation is to extract from the source; it does not generate room reflections like Audyssey DSX or Yamaha DSP modes. Rather, it is more like Pro Logic IIx, Logic7 or Neo:X which also extract from the source to create their effects. But there are significant distinctions with IAP. Whereas these other surround decoders can “steer” signals from certain channels to other channels, the IAP avoids that as a general rule. The main exception being the extraction of a steered center output from stereo content. The degree of steering is completely adjustable from Off (phantom center) to 100% (all steered to the center speaker) in some two dozen steps. Because the IAP uses frequency-selective steering, it performs this task with minimal impact on L/R imaging. As with PLIIx Music, I set the Center to 1/3d of the way from phantom, just enough to fill in the combing notches caused by phantom center, nicely improving the naturalness of vocals.
For 2-ch sources, the IAP also offers an option called “Matrix Decode” which takes advantage of surround encoded content (e.g. Dolby Surround or PLII) and steers surround effects to the rear speakers—and does an excellent job of it, too. Unless the content was surround encoded, which nowadays is old movies, I recommend leaving Matrix turned off just to make sure no unwanted surprises happen.
This is where IAP steering activity ends.
When PLIIx or Logic7 are used in a 7.1 system with 5.1 content, they steer correlated signals in the content’s Ls/Rs channels among the 4 surround speakers. In contrast, IAP takes a less active approach. It maps the Ls signal equally to both the Ls and Lb speakers, and Rs comes likewise from the pair of surround speakers on the right. In a directional sense, IAP is simply maintaining the 5.1 mix with no added interpretation.
With stereo content, the trusty legacy surround modes do quite a job reallocating sounds to the surround speakers, widening the L/R soundstage and contributing notable surround effects. IAC does none of this—the L/R source remains solidly in the L/R speakers (and in C to whatever degree you desire).
Whether the source is stereo or 5.1 discrete, the IAP is clearly taking a purist approach in preserving the original mix.
So if the IAP is not doing any of the unusual surround steering, what comes out all the surround speakers? I’ll call it ambience. Anything that was not correlated in the source content. Direct sounds like vocals or percussive transients are not present, but their reverb and ambience are extracted and presented among all the speakers, from what I can hear, rather uniformly but decorrelated to make sure they cause no obvious localization. In a basic sense, this is actually what most prior surround processors intended to do, but wideband steering with relatively simple control logic just could not get there. IAP raises the art and finesse of the process to a level I have never experienced.
With every other process I have auditioned, including my all-time favorite, PLIIx, there comes a point in the listening where the surround process goes from being a positive effect to a negative. Where that threshold lies for any given person may be quite different—some audiophiles will avoid surround processing entirely (let alone EQ or a separate subwoofer), and other listeners seem happy enough with rather gross manipulations of the sound. I’d say PLIIx falls somewhere between, with an effective degree of surround being presented but handled with a high degree of respect to the mix balance and timbre of the original. Yet, there are times when the surrounds are a little too overt. It’s not that the surrounds are loud, but what comes out is not so much ambience but more direct cues, and that can confuse the perception. The IAP’s ability to dodge direct cues and extract only ambience, and to do so without exposing all manner of weird side effects along the way (has happens all too often), puts it on another plane altogether.
The IAP offers various adjustments for its processing toolchest, and you can build multiple presets to save different settings and call them up instantly. You might like to use a different preset for 2-ch music than for 5.1 movies, for example, or for classical vs. pop.
As with any signal processing tools, they can be adjusted to do more than you might like. The IAP ships with three canned presets, 1, 2, 3, each with progressively greater effect dialed in. At first I had to use preset 2 or 3 to get a sense of what the IAP was doing, since normal “surround upmixing” was not part of the equation. The more I listened and learned what was happening, the more I gravitated to preset 1, which I have since modified from the default (my settings: Center = 7; Depth/3D = 16; Immersion = 9; Brilliance = 16; Room = Off). It seems to me that the Immersion control was by far the most overt in its effect, with just a couple of clicks either way making an audible difference. With my version of preset 1, the obviousness of the overall IAP effect is most easily noticed when it is turned off. The sense of space reduces, and it’s as if the rear of the room has dried up. You are no longer sitting in a nice, cohesive acoustic space, but a small room with stereo sound piled up front. A reverse LEDE effect, if you will.
Having long ago transitioned away from “pure stereo” as my preference for audio reproduction, I nonetheless do find PLIIx sometimes too invasive as mentioned earlier. Yet, switching to stereo goes too far to the other extreme, and I soon revert back to PLIIx. In comparing the IAP to PLIIx and stereo, what became clear is that the surround contributions from PLIIx, being rather simple, unfiltered and unprocessed extractions of the source (i.e. you can often identify the source in them when solo’d), when heard in combination with the main source signals, affect the sense of timbre to a small but definite degree. This is much the same timbral coloration effect a specular reflection from a speaker can impose onto the direct sound. This effect occurs with PLIIx regardless of how well the surround speakers match the front speakers.
In contrast, even though the IAP signals are also derived from the source, the way they are isolated/decorrelated prevents them from interacting with main signals in this way, thus completely avoiding altering the timbre of the source. In an ironic sense, the rather significant processing of the IAP works to better preserve the original qualities of the source better than the simpler and “purer” signal path of PLIIx. To illustrate the point further, consider the “All Stereo” mode which has no processing whatsoever but is extremely invasive to the original signals both in terms of imaging and comb filtering resulting from multiple arrivals of the same signal.
The IAP fills the gap between direct stereo and PLIIx so successfully that I happily enjoyed it for hours without feeling “surround” deprived. And one thing is abundantly clear: I’d never opt for plain stereo again. Whether “purist” stereo aficionados will feel the same, time will tell. But if not, I think they would be missing out on an extremely powerful yet subtle technology that enhances the enjoyment of stereo content.
What abut 5.1 sources? With the excellent 5.0 recording of the Vänskä/Minnesota Beethoven Piano Concertos 4/5, I always felt the acoustic space was beautifully portrayed. Yet with IAP it becomes more seamless and more natural feeling. With the Reiner/CSO 3.0 SACD of Pictures at an Exhibition, the space feels a little vacant in the back. IAP fills it out subtly but effectively.
The above is but a fraction of what the IAP can do. Please read the manual for more insights. In my opinion, it’s all gain with no pain. In spite of my limited 7.1 use case, it brings appreciable value to the party.
I think I have the only unit in the U.S. at the moment. As many of you are clustered in the PNW, perhaps Amir/Madrona would like to try it so folks could hear it in action. That could be arranged.