By Peter M. Bracke

Beyond what was written in the introduction to my first DTS DVD review of Antz, I thought it might be useful to explain exactly how my system is set up, how I do my comparison reviews and the thinking behind doing them the way I do, as well as some words on the ratings system.

The System

On the video side, my RPTV is calibrated to NTSC standard 6500 degrees kelvin color temperature by an ISF-certified technician. This was done once over a year ago, and again last week, August 19th. On the audio side, all channels are calibrated to 75db reference level using my trusty Radio Shack analog sound pressure level meter. I check this every couple of weeks to make sure the levels haven't drifted, always making certain to do so before I do a review.

Another important thing to mention here is that like many processors my Lexicon has a setting that limits the signal peaks sent to the subwoofer channel. Called the Subwoofer Peak Limiter in my processor (and some variation of that in other processors) this setting was created because the low frequency peaks found in the LFE channel in discrete 5.1 channel DTS and Dolby Digital soundtracks can be 10-15db louder than the low frequency peak levels attained in matrixed Dolby Surround presentations. Many subwoofers on the market simply aren't capable of reproducing those kind of peaks at high volume levels and could sustain damage as a result. My Mirage BPS-400 however, is not one of those subwoofers and I have the Subwoofer peak limiter defeated. I think this is important to mention because even in my processor this limiter is engaged by default, as I'm sure is the case with many processors, and must be sought out to be defeated. If subwoofer peak limiting is engaged the listener will not hear the full output of the LFE channel.

I think another thing worth mentioning here is that I do not engage re-equalization of any kind while performing these comparative reviews. THX Re-Eq and the like can do a good job of taming the often hot high frequency response of some soundtracks. In fact, sometimes when I'm viewing for pleasure, as opposed to the torture that is involved with reviewing, I do engage Re-Eq to tone down a harsh soundtrack. But I think its important that Re-Eq of any kind, THX or otherwise, be left off for this kind of software review. To hear everything that's on a soundtrack, I can't have the upper frequency extension of a soundtrack rolled off.

My point here is that my system is calibrated on regular basis and that when performing reviews I do not have anything engaged in the processing end that would alter or limit the frequency or dynamic response of a soundtrack in any channel in any way.

The Method Of My Madness

I sit down and watch the entire DTS DVD first. I turn the overall volume level up to whatever level I am most comfortable with, and make a note of it. This is usually within 2-3db of reference level, plus or minus. As you're all aware there are differences from title to title on the overall volume level of the disc. If it is too loud at reference level I turn it down a couple of db, if too soft I turn it up a couple db. I also take notes during the movie, marking sequences that look or sound particularly good. When the movie is over I take my notes and begin comparing the two discs on that basis, watching and listening to the noted segments of the film in each format. I also match the overall volume level of the Dolby Digital disc to that of the DTS disc, and make sure that as I switch back and forth between the discs I match the overall volume levels of each disc upon each switch. The overall volume matching is done by ear, and more on that will follow below.

As you can guess from the talk of switching discs, I only have one DVD player and switch the discs for comparison. I usually spend 1-2 hours comparing the two discs. What I try to do with my DTS reviews is give you, the reader, my impression of the experience of watching and listening to a DTS DVD in much the same fashion as you would experience it. I think that the above steps taken to create the review conditions are the most that can assumed taken by the reader who might grab a DTS DVD and put it in his/her player and hit play.

Now, the rub that comes in at this point is that I compare the DTS DVDs to the Dolby Digital versions of each title I review. Most of the reviews of this nature that have been done have gone through great pains to match the overall volume level of each disc in each format and on top of that have tried to level match each individual channel level. I have chosen not to do this for a few reasons. First, and foremost, I don't do this because I don't think you would either. I think most people who might buy or rent one of these DTS discs are going to put it in their DVD player with their system as it is. I think most of you have a subjective level of volume that you find comfortable, and you determine that by ear as I do. I don't think a review can be called invalid when it recreates the end user experience.

I think an important thing to note here is that most of the comparisons I've read have been done as an attempted assessment of the formats as whole. While it might not seem there is a difference between that and what I'm doing, there is. I am trying, on a title by title basis, to tell you which disc gives you the most value for your money. The soundtrack quality is one factor among many. Video quality, price, and features all come into play. I do put the choice to you in terms of "DTS or DD" but I really am talking about the DVD package itself not each format per se. The second reason I do my reviews this way is that I don't think the level matching I've seen in other reviews is necessarily accurate. In the case of overall volume level matching the two formats, the only way I know of to do this is by playing sequences of the DVD in question in each format and measuring the volume with an SPL meter, which as I mentioned, I do have and know how to use.

The problem I have with this is that matching with sequences from the film on each disc doesn't account for any differences there might be in dynamic range between the two formats. If I play a sequence in which one format hits a higher dynamic peak, I would read that on the SPL meter as a difference in volume and wrongly turn down the overall volume of one disc or the other! I think this would be a very easy mistake to make, particularly if the differences in "volume level" tended to be in the 1-2db range. As far as matching the individual channel levels goes, I think its wrong thinking to match the DTS and Dolby Digital channel levels without knowing which is accurate compared to the original soundtrack master. Without knowing which is true to the master, how can you tamper with one or the other? Why dumb one soundtrack down to match the other when you don't know which is correct compared to the levels of the soundtrack master?

And again, the only way I've seen the channel levels matched is with an SPL meter with each disc. Can you tell me you really think it accurate to play a rumble sequence from each version of a disc and measure the subwoofer output with an SPL meter? What do you play to match the surrounds? And again, in either case how do you know your adjustments aren't wrongly compensating for dynamic range differences? This method of matching levels assumes that one of the soundtracks is right, but without knowing which one, is highly questionable. Aside from that, if one sounds better as is than the other, do you care which is "accurate" or why? The whole reason I brought up the idea of doing these reviews to our editor is that I read the reviews that were done with all of this level matching and found them to be less than useful.

In one case more than 75-85% of the article was devoted to how they did the comparisons, and only the remainder to what the reviewers actually heard when watching the discs. I came out of that article not having any more idea of what to expect from a DTS DVD than I did before I read it. I want people to be able to read my reviews and get a pretty good idea what they're going to see and hear, in terms of audio and video quality and supplements, and have at least one strong opinion on which version is worth plunking down hard-earned money to buy. I didn't want people to read my reviews and think, "Gee, if I change this channel level 2dbs, and this one 5dbs, then I might hear what the reviewer heard."

How do they rate?

Peter and I have decided that moving forward my ratings will include disc ratings for the DTS DVD and the DD DVD. My reviews are really of the DTS DVD itself, with the comparison to the DD being part of the review. But I do concentrate on the differences between the two formats in quite a bit of detail, because I think a lot of people want to know exactly what constitutes any perceived differences between them. And when one version sounds better I think that sometimes this could give an impression that the other doesn't sound good at all, but really this is never the case. I think the disc rating section is a good way to quantify the differences between the discs in a way that the actual audio, video and supplements sections of the review might not.

Last, I want to give you a point of reference for my ratings. The most difficult thing about ratings is deciding what they mean and being consistent. If 5 stars is your highest rating, what happens when a disc comes along that sets a new standard? Advances are constantly being made in authoring techniques and in the transfer process itself. How do you account for giving a certain disc a 5 star picture rating today and six months or a year later something comes along that looks better? How will today's best discs look if someone gets their act together and does an all-digital anamorphic transfer of certain computer-animated features someday? Does that feature then get a 5+ rating, or do you move your scale to 6? For now, my preference is to be a bit conservative. A disc that rates 4 or 4.5 stars is an excellent disc, with 5 being reserved for something that is truly reference quality.

The question always comes up when a disc is excellent but perhaps just shy of that level that is the best that it can be given the current state of technology. I guess I'm just trying to say here is that because a disc is not a 5 star disc in one rating area or another is not saying that it isn't outstanding. I will move forward with this for now, and when a benchmark is achieved I will make note of it, indicating that a new standard of reference has been established.