About a year ago I re-calibrated my 5.1 system again, so I can relate a few insights from having done that.
I’ve never used MCACC, but my receiver has Audyssey and I’ve been letting it do its thing with EQ and time correction for the speakers. The results seem to be quite dependent on giving it accurate measurements, so it can potentially end up sounding weird if this isn’t done correctly, but if you do it right it can be remarkably good at balancing the level and tone of each speaker. Before running the measurements you should do everything possible to make the room itself suitable; make sure the speakers are ideally placed at the proper angle and distance from the listening position; try to avoid putting them in the corners to avoid boominess, etc. If you can (as in, if money and space aren’t an issue), try to add bass traps and diffusers to cut down on room reflections, which can be particularly nasty in smaller rooms with hard parallel surfaces. Corrective EQ alone can give great results, but chances are the correction will only actually sound good within a small area of the room unless the larger acoustic issues are dealt with. Acoustic treatment makes the room correction have to work less hard, enabling it to sound good within a wider area. Doing this properly is out of the realm of realistic possibility for many people, but it’s something to look into if you can.
I have found that dialing in the subwoofer to blend with the main speakers can be the trickiest part of setting up a system like this, but it is very rewarding once you do get it right. Room issues are particularly problematic with bass, and you will almost always end up with huge jumps in loudness between different frequencies. Because my receiver only seems able to correct the main channels, last year I decided I’d had enough of my room’s unevenness and ended up getting a miniDSP 2x4 HD to handle subwoofer EQ. After some trial and error doing measurements with Room EQ Wizard, I was able to dial in a very smooth response that is almost perfectly flat at my listening position throughout the sub’s operating range. This made a huge difference to the tonal quality of the bass, and it has made it much easier to trust the results and know that it will sound correct in other rooms and on other playback systems. The 5.1 mix for 4K83 is the first project I worked on with the miniDSP after doing this, and I noticed right away that I was able to dial in the LFE levels far more quickly and reliably than I ever had on any previous version.
One thing to keep in mind is the Fletcher-Munson effect. Human ears are not very good at hearing low frequencies compared to the midrange, so many people often complain that flat bass response sounds weak and boring. Since this perception is rooted in the science of how we hear, applying some amount of bass boost to compensate is a valid thing to do. The question becomes how to do this, and how much. Using a system with Audyssey, I always engage the ‘Dynamic EQ’ feature, which is essentially a Fletcher-Munson compensation curve applied during playback. Low frequencies are boosted in relation to the master volume setting; the lower the playback level, the more boost is applied, and the very low bass notes are pushed up to a greater extent than the upper bass. Our hearing is closest to flat at 85 dB (C-weighted), so movie theaters are calibrated for a flat response at this level, with 20 dB of headroom above this in the main channels (30 dB for the LFE). In the acoustics of a small room in one’s house, playback settings louder than -15 dB or so from reference level tend to be far too loud for comfortable listening, so at lower levels the bass response is almost inevitably going to be too weak unless it is boosted beyond flat to some extent.
With the typical low end boominess found in most rooms, chances are you can just measure the sub with an SPL meter, set it to the same output as the speakers, and its total level will sound approximately correct even though the frequency response is all over the place. This is exactly what I had to do before I got the miniDSP. But once you actually set up your system for a flat response and do any kind of critical listening on it, it becomes equally important to listen at the right level to make things sound even. At 85 dB no bass boost is required, but below that it is actually essential if you don’t want it to sound too quiet. Audyssey’s Dynamic EQ tends to make things sound boomy if there isn’t any subwoofer correction applied, but with a flat response, it boosts by just the right amount. I’m not sure what MCACC does about this, but it may be necessary to apply some kind of custom ‘house curve’ if it doesn’t automatically compensate for lower playback level. Such a custom curve would only be completely correct at the volume setting at which it was measured, but it would be better than not having one at all.
Another thing to think of is the potential effect of Dialog Normalization, which reduces the total playback volume by a set amount (usually -4 dB for tracks that use it). Dynamic EQ is supposed to compensate for DialNorm and apply more bass boost, but on my receiver they seem to have forgotten to implement this. I noticed right away after setting up the miniDSP that movies with DialNorm had significantly weaker bass than they should have (comparing Dolby tracks at -27 DialNorm vs DTS versions of the same mixes with no reduction made this really obvious), so eventually I ended up creating my own ‘house curve’ to use on DialNorm tracks. I started with the same EQ settings as before but applied 3.5 dB of additional gain to the subwoofer output, along with a 2 dB shelf filter below 40 Hz. These settings are only completely correct for tracks with a DialNorm setting of -27 at a playback level of -11 or so (-15 after the reduction), but it’s been working well for me for many movies and TV shows that have DialNorm applied. If your receiver doesn’t have Dynamic EQ then obviously this workaround isn’t directly applicable, but it’s something to keep in mind when considering whether to implement a bass boost that will work with your preferred volume setting.
The issue of needing to ride the volume knob to compensate for dialog being too quiet compared to action scenes is unfortunately a very common problem these days, and it has a lot to do with digital mixing and its lack of safeguards against abusing headroom. (I talked about this at some length in my post on the 4K83 mix.) A lot of people seem to regard boosting the center channel as a go-to solution for this, but remember that many sound effects may be mixed into the center in addition to dialog – if you do this they’re just going to get boosted too, so it’s not really ideal. I’m not especially in favor of unbalancing a playback system to compensate for mixing deficiencies… a potentially better thing to do, if the action scenes are too loud, would be to compress the dynamics (with ‘Night Mode’ or whatever they call it) when listening to material that has bad dialog levels. That way all of the speech will be intelligible, while the peaks will be cut down to something that won’t blast your head off. Using compression shouldn’t be necessary during any of my Star Wars mixes – I went to a great deal of trouble with 4K83 in particular to ensure that it wouldn’t be – but unfortunately there’s a lot of material out there that doesn’t take adequate consideration for such things.
Now, about demo-worthy scenes… captainsolo is correct that there isn’t really that much “flashy” surround usage in the original mixes for the Star Wars films. Usually they only used the surrounds for ambience, so it’s not the kind of thing you’ll notice right away unless you’re specifically listening for it. The mixers approached them knowing there was a good chance any given theater wouldn’t even have surround speakers or subwoofers hooked up at all, so their primary goal was to make the movies work with just the front channels and only add in the rest afterwards for extra flavor. There are stand-out moments here and there, of course: right at the beginning the rebel blockade runner can be heard from behind before it appears on screen, Obi-wan’s roar to scare away the sandpeople swoops from front to back and fills the room, the sound of his lightsaber in the cantina emanates from all speakers at once, etc. Luke can be heard in the surrounds deflecting blaster bolts on the Falcon, his and Leia’s speech just before the chasm shootout echoes from behind quite obviously, and there are several instances of the Millennium Falcon and other ships panning from front to back or vice versa. It doesn’t sound like a modern movie with lots of surround effects moving all over the place, but it’s just a matter of adjusting your expectations. I actually prefer this sort of mono-surround mix to a lot of the more recent stuff, because they tend to be more balanced between all the different elements. The special editions are way more flashy in this respect, but I find them kind of crass because it’s so obvious that all of the new sound effects are mixed a lot louder than the ones that were already there.
Anyway, as long as you aren’t downmixing it anymore, I’m sure you’ll think it’s fine… 😛