OK, it's Saturday morning and since I'm on call-out for work I ain't going anywhere. An ideal opportunity to tidy up all those bits of paperwork - and do a complete speaker level calibration of my system. I try and get this done every couple of months. Not because anything really changes (unless speakers have been moved for whatever reason), but really just to confirm to myself that the system is singing as it should. This time, rather than use just Avia, I calibrated using all the tools available to me. Avia, Video Essentials (DVD and LaserDisc) and the internal test tones of the amp, along with the DTS technology setup CD for the Millennium DTS decoder. I wanted to see what differences - if any - using all these test tones would make. I was really hoping that there would be no - or at least very little - discrepancy between them. What I found has left me unsure and really quite sceptical. Rob's Stuff[*]Denon AVC-A1 THX certified amplifier[*]Millennium 2.4.6 DTS decoder[*]Kef Q65, Q55, 200C loudspeakers[*]Boston Acoustics VR2000 THX certified subwoofer[*]Panasonic A110 DVD player[*]Pioneer CLD-HF9G LaserDisc player[*]Sony KV-32WF1 32" 16:9 TV[*]IXOS, Chord Co. and SonicLink cabling First of all, the Radio Shack SPL meter was set up in the prime listening position, pointing more or less straight upwards. It was positioned on the back of the central chair in the room in such a way that it could do it's thing hands-free and with me not in the way of the signal. The chair tilts back you park your backside, so the SPL was pretty much in the same position as your head (well, OK, my head). The calibration level was 74db, simply because I was able to get the needle resting more accurately on this postion that at 75. The mode used was plain AC-3 and External Input for the DTS decoder. No DSP or THX processing was applied. Also, the Dolby Digital Dialogue Normalization was turned OFF. [*]Internal test tones Starting on Front Left, the overal volume was raised until the SPL needle hit 74db dead-on. Overall volume was then left alone. Results: Left: 0db Centre: +1db Right: +2db Rear Right: +1db Rear Left: +1db Sub: +2db *NB: The +2db increase on the front right channel is attributable to the room acoustics. [*]Avia Same as internal tones (good so far!) [*]Video Essentials DVD Left: 0db Centre: +1db Right: +1db Rear Right: +1db Rear Left: +1db Sub: 0db Notice the front right had to be dropped by 1db and the Sub by 2db compared to the internal and Avia tones. [*]Video Essentials LaserDisc Left: 0db Centre: +1db Right: +1db Rear Right: +1db Rear Left: +1db Sub: -11db The VE LD obviously does not include the 10db alteration of the LFE channel as required by the Dolby Digital spec. Even so, it still appeared to be 1db higher than the DVD. Now, the tones on Avia and Video Essentails do not sound the same to the ear. Those in VE have a softer, less harsh spectrum of frequencies - more 'pink', if you will. This may explain the 1db discrepancy in the front right, but the 2db difference on LFE left me completely confused. Granted, the sub is probably not in an ideal position (between TV and front-right), but due to room limitations, there's not a fat lot I can do about it. As a result, I can never get the LFE test tone to 'sit' with any accuracy. It always likes to bounce that SPL needle around, making the measuring process less than satisfactory. Even so, 2db is a very audible level difference when listening to a film soundtrack. Finally, the Millennium 2.4.6 DTS decoder was calibrated using the DTS Technology setup CD supplied with it. First of all though, the Milly's own volume level had to be matched to that of Dolby Digital. This isn't really that necessary when just getting the individual levels correct, but it makes cross Dolby/DTS comparisons a lot easier. The only way I could really get this done was to play an Avia[ front left test tone at 70db dead-on, and then play the DTS front left tone at the same volume level on the amp, but with the Milly's own volume knob adjusted accordingly. The end result was that with the test tone, both Dolby Digital and DTS hit the exact same SPL level at the same given amp volume. DTS results: Left: 0db Centre: +2db Right: +2db Rear Right: 0db Rear Left: +1db Sub: -3db The results cannot be compared directly against the Dolby Digital levels because the Millennium has it's own surround, centre and LFE trim controls on the front panel. But, since the DD and DTS test tones now hit the same SPL level, they should be pretty accurate against each other. So, what we have is Avia giving the same results as the internal tones and Video Essentials giving slight differences with front right and sub level. If anybody can provde any reasonable explanation, please do. I mean - which are you supposed to trust? Since Avia and the internals match, I'm tempted to go with those, but can anyone really say for sure? But, I suppose the best test is run a soundtrack or two through the system. The ideal candidate was the new Twister DVD as it features an aggressive, envloping soundtrack and allows DTS and DD track selection on the fly (though the amp source still needs to be changed). I suppose the object of the excercise was really to see if my intial impression of the Twister DTS sub level being lower than the DD was correct. I'm sorry to say, that even after a good hour of calibrating, the same impression was there. An example: In the opening 1969 scene, we see a shot of young Jo being woken by the sound of the oncoming storm. Just as she turns her head, there is a very deep sounding thunderclap that can really be felt. On the DD track, all was well. One of the shelves holding my discs rattled in sympathy. The same scene in DTS did not have the same bass depth. It was almost as if the sub level had been smoothed out, resulting in a sound heard more than felt. A little experimentation was required. I switched back and forth between the two formats, raising the DTS LFE level by 1db each time. It was not until I raised it by 3db that the same level of bass was felt. So - is the Twister DTS track really 3db out or is there a setup problem in my system? I'm really not very happy with the sub calibration for either format, but since moving the woof isn't really an option, I dont see what I can do about it. This has turned into a rambling post, but if anyone can shed any light on what is going on, or provide any tips, I'm all ears. ------------------ "It's all in the mix"