ial details, sounds just convincing enough to subliminally take you across this threshold of believability, then you are IN the concert hall or IN the film venue.
      Audio quality plays a far more important role than video quality here, since you are surrounded by and immersed in the reproduced audio environment all around you, whereas the reproduced video is only on a screen in a limited area in front of you.
      The Arcam AVR600's transparent ability to reveal sonic details, more realistically than we have ever heard them before, is a crucial key in taking you across that threshold, into the magic of believability. The AVR600 stands alone in its ability to take a quality system across the threshold, from fake to real.


      In our review of Arcam's earlier AV8 surround processor, we noted that space is the final frontier, and we discussed why it's so important for your system to be able to portray a believable surround space, to enrich your experience, both for music and for film soundtracks. Since then, we have chronicled the improvements in surround space portrayal achieved by successive Arcam products, the AVR300 and then the AVR350. The AVR350, with its new mask of silence technology, achieved a blacker background and better intertransient silence, which, together with improved basic transparency, allowed the very subtle sonic cues that define space itself to shine forth more clearly, thereby creating the best, most convincing surround space we had heard to date.
      So we conducted direct A-B's of the new AVR600 against the state of the art in surround space portrayal (which happens to have been Arcam's own AVR350). It was shocking. The AVR600 re-creates and portrays a surround space that is about 10 times bigger! The AVR350 already made the walls of our listening room disappear, and transported us aurally to the recording venue, which was a larger alternative space (assuming that venue was large). The new AVR600 makes that alternative space about 10 times larger, hence much deeper, wider, and higher.
      The AVR600 is also far more accurate in defining where the walls of the alternative venue are (e.g. the concert hall or cathedral walls), and where the echoes and reverberant ambience are coming from and bouncing off of. This of course enhances even further the believability of the new, 10 times larger space you have been aurally transported to, since you can now also clearly hear the boundaries of that space.
      Additionally, the AVR600 is far superior at reproducing a halo of believable space around each voice, each instrument, each sound effect. This halo of space around each direct sound source helps to better localize each such direct sound source, in relation to the overall surround space (you can better hear that this direct sound source is right over there), which greatly helps the overall realism of the total sonic picture, hence greatly helps your involved immersion in the whole experience. This halo of space around each direct sound source also makes each sound source itself sound more solid and three-dimensional, hence more believable, again making your whole experience even more believable.
      In comparison to the AVR600's towering performance in portraying surround space, other high end processors and receivers collapse and compress the space, portray it vaguely and amorphously instead of believably. They render direct sound sources (sprinkled around the surround periphery) as flat cardboard cutouts arranged in a simple flat circle around you (i.e. located at a uniform distance from you), whereas the AVR600 renders them as three dimensional solid entities, located at different varying distances from you, in the rich three dimensional space all around you.
      As one nears sonic perfection, the laws of physics and engineering dictate that further improvements must become incrementally smaller and smaller. Thus, with Arcam's new AVR600, we were hoping for some improvements perhaps, but we were not expecting big improvements, when we conducted direct A-B comparisons of surround space imaging, against other state-of-the-art electronics (including the AVR350). So there was much jaw dropping and gaped amazement when we heard how the AVR600 portrays a 10 times larger surround space, and defines it much better.
      Thanks to this hugely expanded surround space, and its much better definition and delineation, the AVR600 gives you a whole new level of believability, in transporting you out of your listening room and into the alternative venue of the recording. That magic of believability is what home entertainment (both music and film) is all about, and the AVR600 delivers this magic in spades, as no other electronics ever has.
      A large share of the credit, for the AVR600's huge improvement in surround space imaging, has to go to its dramatic improvement, over the previous state of the art, in transparency and intertransient silence, discussed above. The sonic cues that define space, such as hall reverberation patterns, are very subtle and delicate sonic information contained in each recording, so it requires the utmost transparency to resolve them as meaningful spatial information, and it requires the utmost in intertransient silence to reveal them (rather than burying them in noise energy left over from a previous strongtransient).
      Indeed, the objective and perceptually measurable fact, that the AVR600 portrays a large alternative venue as being about 10 times larger than the previous state of the art could, is therefore a good objective indicator (and measure) that the AVR600 resolves and reveals this subtle spatial information about 10 times better, so one can reasonably say that the AVR600 is 10 times better than the previous state of the art in transparency and intertransient silence. Here's an example of the good objective grounds why we call the AVR600 a stupendous engineering achievement (we're not just blowing the smoke of reviewer hyperbole).

Enhancing Surround Space

      The AVR600's ability to convincingly enhance 2 channel and 5.1 channel material to 7.1 channels, via Dolby PLIIx, is also a vast improvement over the previous state of the art. The fidelity of all channels, that have been put through the matrix enhancement derivation process, is better than we've ever heard before. And the generated surround space enhancement is far more convincing than we've ever heard before. Also, the occasional steering artifacts (pumping, etc.) are remarkably reduced. Some of these Dolby PLIIx improvements are doubtless due to the AVR600's dramatically improved ability to transparently and more accurately reveal subtle detail information, including the subtle phase relationships that Dolby relies on for its matrix extractions and logic steering. We suspect also that Dolby themselves might have been subtly tinkering with the PLIIx process, as built into the very latest products, for example by making the time constants shorter for quicker logic steering with less audible pumping.
      The AVR600 is truly amazing in utilizing PLIIx for creating a believable surround space with 7 loudspeakers. So much so that we would urge everyone to invest in a system with 7 loudspeakers, of as high quality as your budget and listening room space allows. And of course buy an AVR600 to run it. When you have 7 loudspeakers, you can use the 2 back surrounds, spaced 60 degrees apart, to a richly ambient, believable space in back of you (and indeed for the entire rear hemisphere), while you use the 2 side surrounds (directly at your sides) not merely to reproduce side sounds and side hall ambience, but even more importantly to magically, amazingly widen and deepen the stage up front, where most of the action is (with both music and film soundtrack recordings). Note that most surround recordings are now professionally mixed for loudspeaker placement at 60 degree increments around a circle (plus the center channel), which means that you should employ 7 loudspeakers (at these same 60 degree increments around a circle) to play these surround recordings correctly.
      If you are limited to 5 loudspeakers, you will still hear vastly superior surround space from the AVR600 than you have ever heard before, from any other electronics. Indeed, even if you are a 2 channel stereo music buff, you still need to get the AVR600 for your music playback. We deliberately tested the AVR600 playing 2 channel material through just 2 loudspeakers, and even here the AVR600 portrayed 10 times the volume of space than we had heard before, with much richer depth, ambience, width, and localization precision, on the stage image portrayed in front of us.
      My library contains about 10,000 two channel music redbook CDs, and nearly that many two channel music vinyl LPs. So I probably spend 10 hours music listening for every hour watching films. I listen to all this music through now the Arcam AVR600. Why? Because the AVR600 gives me the best sound I have ever heard from any system, and does so equally for music and for film soundtracks. Indeed, since the basic fidelity of many music recordings surpasses the basic sonic fidelity of most film soundtracks, music recordings appreciate and take full advantage of the AVR600's vastly superior sonic performance, even more dramatically than most film soundtracks do.
      If you are smart enough to build your home theater system for the best sound you can get, then you will want to also use it for your music listening, so this one system serves a dual function, saving you the money of having to build a separate 2 channel system for music only. And now I'm telling you that, if you are smart, you will install the new AVR600 as the heart of your system.
      If, on the other hand, you have a system dedicated only for music, I'm telling you here and now that you also want an AVR600 for that music-only system. The AVR600's sonic fidelity is so manifestly superior that you are cheating yourself if you employ anything else. Yes, I know it's only a receiver. But sound is sound, and it's my job to tell you the truth about what I objectively find in my research investigations.
      If you have a music-only system that is merely 2 channel, you still want the AVR600 for its superior fidelity, even as a simple amplifier in 2 channel direct mode (the very mode we first tested it in). But, after you install the AVR600, we would urge you to take advantage of its stunning surround space performance. The AVR600's surround space enhancement of 2 channel recordings, recreating a realistic surround space and immersing you in a concert hall experience, has to be heard to be believed. You like me might have a substantial investment in a library of 2 channel music. Now is the time for you to revisit your library collection, and re-hear all your best recordings, but this time as a totally different, concert hall experience. It's simple to accomplish; just get an AVR600 and add some loudspeakers.
      The AVR600, with its PLIIx enhancement of 2 channel recordings, creates a concert hall ambience around you and transports you into a huge concert hall (you can literally hear audience members coughing and rustling all around you, on live recordings). Even more importantly, the AVR600 makes the stage, and all the musicians on stage, much more three dimensional, solid, and vividly believable, with space and air all around them (if you switch back to straight 2 channel stereo playback, the whole stage up front actually collapses and shrinks, and the musicians turn into hollow phantoms, flat cardboard cutouts).

III. Technical Analysis

      The Arcam AVR600's sonic performance is stunning in many ways, and its technical design is likewise stunning in many ways. But pride of place has to go to the power amplifier section of this receiver. That's because the power amplifier is the most challenging section to make really good, within the confines of a receiver's chassis and budget limitations.
      In judging the sonic performance of the AVR600's power amplifier, we were effusive in praising its many areas of superiority, indeed its milestone breakthroughs in setting new standards for the state of the art. Are our effusive judgements perhaps the figments of golden-eared imagination, or overly enthusiastic raves? No. The Arcam AVR600 in point of fact fully earns all that effusive praise. You see, there are good scientific reasons why the AVR600 sounds as remarkable as it does. The AVR600 abounds in technical innovations that are far in advance of other surround receivers, and even ahead of most expensive high end separates, such as dedicated monoblock power amplifiers. These are the concrete, real world factors which explain why the AVR600 does in fact sound so extraordinary, so much better than the competition. You'll see this for yourself, in the following technical analysis.


      Let's start our technical analysis with heat. In any power amplifier, the primary enemy is heat. Heat sets limits on power output capability, on current capability, on device selection and safe operating area, on idling current, on operating class (both kind and degree), on chassis size and design, and on product cost. Generally speaking (and all other things being equal), the better you want a power amplifier to be (in power capability, sonic quality, etc.), the more heat it will produce, which means that the chassis size and design will have to be able to dissipate (radiate away) that extra heat, which makes the chassis much bigger and the product much more expensive. Now, huge size and huge expense can be tolerated in 300 watt dedicated monoblock power amplifiers selling for $30,000 each, if you can afford that kind of money and space commitment. But for mere mortals, size and expense cannot be stretched to such extremes. And then the ultimate compromise is dictated when a design engineer and manufacturer try to shoehorn 7 power amplifiers into the small size and small budget of a surround receiver, while still leaving chassis space and budget for all the other signal processing circuitry of a surround receiver. Again, the primary enemy remains heat. With 7 power amplifiers plus processing circuitry crammed into a moderate size single chassis, selling for a moderate price, the allowable heat budget for each of those 7 power amplifiers must be kept very small. And that small heat budget in turn has dictated the compromised sonic quality and compromised capabilities of each power amplifier channel in all surround receivers.
      Until now. The Arcam AVR600 is the exception. Its 7 power amplifier channels sound as good as 7 dedicated 300 watt monoblock high end power amplifiers. The latter are able to sound as good as they do largely because each large, heavy, separate, widely spaced, $30,000 monoblock chassis can dissipate (radiate away) a lot of heat. But the AVR600's 7 power amplifiers are all packed together, cheek by jowl, within a modest size chassis, and the whole package including surround processor costs merely $5000, instead of $210,000 that just the 7 monoblock high end power amplifiers cost. Thus the obvious question for our technical analysis is, how on earth does Arcam do it?
      The laws of physics apply, even to Arcam design engineers. They can't dissipate a larger amount of heat from a given chassis than the competition does. So instead, they worked to figure out clever ways to get the sonic advantages of a high heat design (like those 300 watt high end monoblocks) while producing less heat. A lot less heat. The result? A unique new (indeed breakthrough) power amplifier design where each channel sonically performs like a 300 watt high end monoblock, yet produces so little heat that 7 of these channels can be put into a modest size surround receiver chassis selling for a modest price.

Rich Class A in Class AB

      As you probably know, power amplifier designs are often grouped into types, based upon the class of operation of their output stage. This is fitting, since the output stage is the principal heat generator, hence the principal player in that unfortunate correlation between heat generated and sonic quality in power amplifiers. Generally, those classes of output stage operation which sound the best also generate the most heat. Class A operation can sound the best, but it also is the worst at generating the most heat (hence requires the largest and most expensive chassis heat dissipation package, for a given power output capability). Class B operation is more efficient, hence generates less heat for a given power output capability. Other classes, such as class D, are yet more efficient, but have too many sonic problems to be seriously considered for high fidelity audio (at least for sensitive, discriminating ears).
      Class B might be somewhat more efficient than class A, producing less of that heat enemy for a given power output capability, but there's a piper to pay, a penalty of worse sonic distortion. And it's not merely the case that class B has a worse degree of sonic distortion than class A. Rather, class B has a whole new kind of distortion that class A doesn't even have at all. Just how bad is this new kind of distortion in class B? Maybe you'd guess .1%, or 1%? How about 100% distortion, or even many thousand percent distortion, or infinity percent distortion!
      How does this happen? In class B, when the audio waveform crosses the zero amplitude axis, the other half of the power amplifier's output stage is suddenly turned on (and the previously conducting half is suddenly turned off). But there are three technical problems. There's a temporal delay before the previous conducting half manages to actually turn off; plus a temporal delay before the new output stage half actually turns on; and then, when the new output stage half finally does turn on, its amplification is nonlinear in the small signal region (near the zero crossing). These three errors produce a momentary distortion (often called crossover notch distortion) in the audio waveform. Because these distorting errors occur when the audio signal is at or very near zero amplitude, the magnitude of the distortion can be as big as the magnitude of what the audio signal is at that moment (100% distortion), or even much bigger (when the distorting error is finite but the audio signal is still zero, during the turn-on delay period, then the distortion during this brief time period is infinity percent).
      Admittedly, this huge percentage of class B distortion occurs only during a very brief time (and amplifier specs cheat by taking advantage of this briefness, since they average the energy of this brief burst of huge distortion over the full sine wave cycle, thereby reducing its apparent magnitude

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