put into each recording's jacket, instead of just one value.
      Note that we could still write down merely one value, say the value of the front mains, on that little card, since the center front loudspeaker is always set 2 dB higher than the front mains, and we could remember that for every recording we set up for re-listening from that little card, but for us it's just as easy to simply write down and then later read and key 3 numbers as it is to later mentally re-do the arithmetic of adding 2 dB to the front mains value when keying in the trim level for the center front. Feel free to do it either way.

5.1 Rears

      The above topic, of doing manual work to help the computer past its shortcomings, raises another issue in the same vein. We strongly advocate using all 7 channels, with 7 loudspeakers (and full range ones, if you and your listening room can fit them in). This gives a much more believable and convincing re-creation of surround space than 5 loudspeakers can. And PLIIx, used to generate the 7 channels, is now so good that the slight losses in fidelity from its matrix derivation are outweighed by its sonic benefits for the surround soundfield, whether the original program has 5 or merely 2 channels. So we are happy to employ PLIIx to drive all 7 channels, all the time.
      But you might sometimes want to play just 5 full range channels (i.e. 5.1 instead of 7.1). You might want to hear the spatial effects and surround soundfield of a 5.1 recording exactly as they were mixed, without spurious enhancement caused by the addition of 2 non-genuine channels. You might want to hear the absolute best fidelity you can from the 5.1 recording, without the slight fidelity degradation that occurs from running it through the PLIIx matrix used to derive the extra 2 channels (this is especially relevant to lossless HD 5.1 soundtracks from Blu-ray, which contain much more information than the lossy 5.1 soundtracks from DVD).
      If you have a 7 loudspeaker surround array, for hearing the spatial surround benefits of 7 channels, but sometimes want to listen to 5.1 material straight, you have to be able to switch between a 7 and 5 loudspeaker setup. In particular, you need to switch the back surrounds between receiving channels 6 and 7 (for 7 channel duty) and receiving channels 4 and 5 (for 5 channel duty) - assuming you have set up your loudspeaker array in the ideal configuration, with the side surrounds directly at your side, and the back surrounds each 30 degrees off the back central axis (in this configuration, the back surrounds are ideally positioned for dual duty, radiating the back surround information from either 7 channel or 5 channel program).
      Now, in most surround processors, as well as Arcam's previous units, there's a useful setup menu called 5.1 Rears. This menu allows you to set up the surround processor at the outset, so that it later intelligently detects whenever you are using a mode like PLIIx that generates 7.1 channels, vs. whenever you are using a mode that outputs only 5.1 channels. Then, based on the choice you had previously made in setting up this 5.1 Rears menu, the processor intelligently and automatically switches the back surround loudspeakers between receiving channels 6 and 7 (when you happen to be in a 7 channel mode) vs. receiving channels 4 and 5 (when you happen to be in a 5 channel mode).
      This 5.1 Rears setup menu, and this intelligent sensing, and this automatic switching, were all provided by the Cirrus chipset, as employed in Arcam's earlier surround processors. Alas, the Analog Devices chipset in the AVR600 does not provide this option at all (no setup menu, no intelligent sensing, no automatic switching of your back surrounds). Thus, with this Analog Devices chipset, the only way to listen to 5.1 material in 5.1 (from a 7 channel loudspeaker array) is to reach around to the back of the AVR600, manually unplug 4 loudspeakers (the side surrounds and back surrounds), and then manually plug the back surrounds into the AVR600's side surround output jacks. Incidentally, if you want to play multichannel SACDs through the AVR600 with a 7 loudspeaker array, you have to plug the cables from your player, for channels 4 and 5, into the AVR600's multichannel input jacks for channels 6 and 7 (the back surround inputs).
      The sonic evidence suggests that this Analog Devices chipset does sound significantly better than the previously used Cirrus chipset, so on balance we're happy that Arcam changed the chipset for the AVR600. Speaking for myself, I'll gladly suffer some manual inconvenience in order to get better sound (a subject that will dominate our next chapter below). But you'da thunk that those Analog Devices engineers might have been a little more savvy about the real needs of multichannel playback.

Video

      As discussed above, the AVR600's breakthrough sonic performance is due in part to technical design features, e.g. multilayer PC boards, which reduce interference and contamination by noise, such as noise from the digital processing circuitry. Thus, it's sonically crucial, and pays big sonic dividends, to keep spurious noise to a minimum. This is especially true with a product that, like the AVR600, reaches perfectionist sonic performance, and does so in part by reducing noise contamination. Competing surround processors have worse internal noise contamination, which gives them worse sonics (more veiled and distorted, with poorer, less black intertransient silence, hence poorer transparency and poorer spatial imaging). But, because these competing processors already have bad noise contamination and poor sound as a consequence, their noise contamination level and their consequent sonics are not worsened that much more if you introduce additional noise into the chassis, say by bringing a video signal in from your player. On the other hand, the AVR600, precisely because it has so little noise contamination internally, and has such incredible sonics thanks in part to this, reveals more clearly the sonic degradation you cause if you bring the noise of a video signal from your player into the chassis. If you do bring video into the AVR600, its sonic performance still stays markedly superior to competing units, so you still want to buy the AVR600, but you simply won't hear the absolute perfectionist pinnacle of sonic performance that the AVR600 is intrinsically capable of.
      Many consumers use a surround receiver or processor as the hub for their entire A/V system, for video signal control as well as audio control and processing. If you are such a consumer and want to keep doing this for the sake of convenience, please do so. You still want an AVR600, because it will still give you better sound, even with many connections and many video signals on board, than competing products can (and its video signal performance is likewise excellent). And you don't need to read about the following inconvenient tweaks in the remainder of this article.
      On the other hand, if you are a purist, and are willing to endure some manual inconvenience in order to experience the very best possible sound (and video), then the rest of this article is for you. Feel free to implement as many or as few of the following tactics as suits your desire, as suits your own sense of the best balance between convenience vs. best possible performance.
      If you are a video purist, you already know that you can achieve the best video fidelity by keeping all video signal paths as short and simple as possible, by employing a dedicated outboard scaler for all video processing, and by calibrating each unit in the chain (rather than relying on a central hub unit like a surround receiver to make band-aid corrections). Thus, you have no reason to bring a video signal into the AVR600. And this will also give you better sound from the AVR600.
      The AVR600 is a superb unit, but it is not immune to the laws of physics and electronics. If you do bring video signals into any chassis, including the AVR600, you degrade the sonic performance. And this degradation is caused via several factors, not just one. First, the high frequency noise of the incoming video signal, brought into the chassis, radiates and contaminates other signal lines and circuits, especially the digital signal processing circuits, which are so vulnerable to spurious, externally induced noise, because noise produces jitter which in turn produces distortion, veiling, smearing, etc. Second, an incoming digital signal prompts the surround processor to turn on its own video processing circuitry and also start generating its own output video signal, all of which radiate even more contaminating high frequency noise within the chassis. Third, these video circuits in the surround processor draw a lot more current from the power supply than the audio circuits do, and their current draw is itself noisy (as dictated by the modulation of the video signal), so when these video circuits are processing a modulated video signal they create a lot of noise in the power supply lines, thereby contaminating all  the audio signal processing circuitry which depends on this same power supply. Fourth, connection to external video sources and loads creates contamination not only via the hot signal wires, but also via the ground wires. This ground contamination might come from simple ground loops (which are sonically very detrimental), or from video noise transmitted via the ground wire (the ground is the reference baseline for all audio signals, so if the ground gets contaminated by video noise then all audio signals likewise get contaminated).
      Thus, if you an audio purist, who wants to hear the best sound from the AVR600, you will join the video purist in not bringing video signals into the AVR600.
      Arcam's previous surround processors put their menus not only on the video output to your display, for a convenient OSD (on-screen display), but also on the tiny fluorescent display on the front panel, one line at a time. Thus, you could actually use all the menus without ever connecting the surround processor to an external video display.
      Now, it's a pain to scroll through all menus and menu choices one line at a time, so we hooked up an external video display, in order to give us the convenience of an OSD, for the entire initial setup process. But, thereafter, the only adjustment we needed to keep changing frequently was the level trim, to optimize the surround soundfield imaging for each recording, and this level trim menu is so simple that it's fast and easy to use the single-line front panel fluorescent display for this function. So we disconnected the surround processor entirely from the external video display after initial setup, not even using the external video display for and OSD, and relying completely on the front panel fluorescent display. And of course this gave us even better sonic performance all the time, because the surround processor was no longer being contaminated by the video noise in the display coming backwards through the video line (both hot and ground). Clearly, then, this simple feature, of putting the menus up on the front panel fluorescent display, is important to all those of you (and us) who want to hear the very best possible sound.
      Although all previous Arcam surround processors include this feature, the early versions of the AVR600 do not include this feature, forcing you to keep an external video display connected to the AVR600 at all times while listening. Arcam has promised to include this feature in the soonest update, after we told them how sonically important it is. Meanwhile, we who crave the best sound can employ two pretty easy workarounds.
      First, for a recording requiring a major trim level adjustment, I simply reconnect the external video display to the AVR600, dial in the best sounding adjustments, then unplug the video display connection again for serious listening to the program at its best. If the program is an audio recording rather than a film, I can get even better sound by also unplugging the external video display from its wall socket (it's not enough to merely turn off that display's power switch), since that display also sends some contamination out via the powerline, which the superbly transparent AVR600 then reveals as subtle sonic degradation.
      Second, for minor trim level adjustments, I can leave the external video display completely disconnected, since I've learned how to do these blind, pretty quickly and easily, even while listening. It involves a simple sequence of button pushes on the remote, and it's easy to count a few button pushes. To help further in keeping track with this blind tactic, each time I press the down button, to switch to adjusting a different loudspeaker in the array of 7, I mentally look at that new loudspeaker location, starting with the left front and going clockwise around the room.
      Incidentally, if you plan to keep this OSD video connected to an external display all the time, we strongly recommend using the old fashioned simple analog composite connection. The composite connection sounds the most innocuous, making the AVR600's sound markedly softer and more tubelike (and, if you do use this connection all the time, it sounds better to keep that external video display fully powered on all the time you're listening, probably because the video circuitry in the display is then fully on, and thus can better terminate the composite video carrier that the AVR600 is always outputting). You might even like this soft, tubelike version of the AVR600's sound, for example if your player has a too brittle solid state sound. But with an accurate player we far prefer to hear the AVR600 sounding clearer without this softening, since the AVR600's intrinsic sound is so gloriously neutral and natural.
      Don't use the 3 wire component output of the AVR600 for OSD, because it tragically makes the sound closed in and collapsed, due to the fact that it creates a horrible triple ground loop with the video display. And don't use the HDMI output of the AVR600 for OSD, because this makes the sound edgy bright, brittle, and distorted in the high frequencies.

Audio Inputs

      Now to audio inputs. For best sound, we recommend using the SP/DIF coax input connections for digital signals. HDMI as a standard and medium has still not cured its awful sonic problems of high frequency distortion, still sounding edgy and frizzy/frazzled and spuriously bright, just as we found and discussed way back in 2007. This is probably due to too high noise and/or jitter, endemic to this HDMI interface itself or to the chips presently used as HDMI transmitters and/or receivers. HDMI must also still be very primitive in waveform crossing detection, making it thereby more vulnerable to degradation by noise and jitter. We proved this by testing a 1.5 foot length of HDMI cable vs. a 6 foot length (which is still very short by HDMI standards, so there should not have been any degradation noticeable or audible). The 1.5 foot length sounded far better (more transparent, cleaner, and faster with better focus and delineation), and in exactly the ways that it should if timing indeterminacy were a problematic issue for HDMI, as it clearly was for the slightly longer but still very short 6 foot HDMI cable.
      The only audio you are forced to bring in via HDMI is a lossless HD soundtrack from Blu-ray. Fortunately, it's easy enough to connect your player to the AVR600 via both SP/DIF coax and via HDMI cable, to different AVR600 inputs, so you can switch to the better sounding SP/DIF input for all program other than lossless HD from Blu-ray (and, if possible, also turn off your player's HDMI output signal when using SP/DIF).
      As to the sound of lossless HD via HDMI, we explicitly tested this, directly comparing the sound of lossless HD brought in via HDMI, against the lossy non-HD soundtrack on the same Blu-ray disc brought in via the better sounding SP/DIF option. It was a tossup, with pros and cons. The lossy non-HD track, via SP/DIF, was cleaner and purer, without the high frequency distortion, artificial brightness, and frazzled frizzines that the mandatory HDMI connection imposed on the lossless HD track. On the other hand, the lossless HD track clearly contained more information, information that was lost and simply absent from the lossy legacy soundtrack. This extra information in the lossless HD soundtrack, missing from the lossy legacy soundtrack, included better detail in the direct sounds, more coherent attack transients, and richer surround spatial imaging.
      So, if you want maximum information and don't mind a bit of artificial bright distortion, pick the lossless HD track via HDMI. But if edgy high frequency distortion actively bothers you, and you don't mind missing some information that you'd never know was missing unless you did this direct comparison, then pick the lossy legacy track via SP/DIF.
      Incidentally, this direct sonic comparison test might well have been unfair to the lossy legacy track, because the disc producer is free to choose different compression rates for the legacy track, imposing different levels of loss and consequently different levels of sonic information loss. On Blu-ray the disc producer has no incentive to make the legacy lossy track sound good, and waste space on this disc by choosing the widest bandwidth, least lossy compression rate of the legacy system, so he might well instead choose a space saving, but much lousier sounding, more lossy compression rate that loses more information, and that might be what we were fed to hear in this comparison.

Ground Loops

      The laws of physics and electronics dictate that ground loops are bad, and inevitably degrade sound quality. If you set up ground loops outside the AVR600, that is not the AVR600's fault, and indeed it's to the credit of the AVR600 that it is so transparently revealing that it reveals these external ground loops if you create them, and of course sounds better if you eliminate them. The AVR600, set up as recommended as the star center ground hub of your system, should then have one and only one ground connection, via only one wire path, to each other electronic component in your system, i.e. to each spoke radiating away from the hub. If there are two (or more) ground wire connections between one pair of chassis (one pair of components), then the two wires and two chassis form a closed loop, and ground currents flowing endlessly around this loop severely degrade and contaminate what should be a perfect ground reference agreement and communication between those two chassis.
      To achieve this single wire path, for each individual other component's ground connection to the AVR600, either you could rely on an interconnect cable between the two units, or (if that other component has a 3 prong IEC power jack for a 3 wire power cord) you could rely on that component's power cord and your house powerline to furnish this ground reference connection. The latter is far from ideal sonically, since power cords and house wiring do not make a good quality ground reference connection between components, for fast, pristine, high resolution signals (they are too long, are not designed for low inductance and high frequencies, and are prone to picking up contaminating

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