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Problems with the THX Optimode tests (1 Viewer)

shankar

Stunt Coordinator
Joined
Feb 4, 2001
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85
I have balanced my speakers with AVIA to read 75dB on the RS SPL meter. I recently got a DVD that had the THX optimode. I wanted to try it for fun and had the following problems.
  1. The speaker levels were not at 75dB when playing with the same volume level as it was when balancing with AVIA
  2. The in-phase Vs out of phase imaging to check the polarity of your connections is indifferentiable
  3. When differentiable (LF Vs Center), the connections suggested by AVIA is the opposite of THX[/list=1]



    What am I doing wrong?? How many of you find this THX feature useful?



    ( I have this other post where I ask what difference does a source make while balacing speakers... I did not include THX in that mix. Only AVIA, VE and the receiver's own test tone)
 

SanfordL

Stunt Coordinator
Joined
Mar 1, 2002
Messages
101
A list? You have a list of questions? Thank God, I thought I was the only one who ever does that. ;)
1. This difference in volume is due to the fact that the THX test does not output at the same level as the AVIA test disk maybe? Not too certain, but that would be my supposition. As long as all of your speakers are playing at a balanced level with the THX, don't sweat this at all, it's a result of your different source materials.
2. What kind of speakers are you using and how are they set up? The in-phase should give you a very obvious source (i.e. the speaker) where the out of phase should sound amorphic. If not, then you got me boss unless you have bi-poles in the front which will sound more omnidirectional - hence the out of phase will seem less obvious. You might try sitting 5 feet away and seeing if the sound changes.
3. Not too certain what you mean.
Good luck.
 

Ryan Schnacke

Supporting Actor
Joined
Feb 5, 2001
Messages
876
I've used the THX Optimode that's on the Toy Story 2 DVD (from the Toy Story 2-pack). I borrowed a friend's Avia and compared the speaker level tones since thats what I use most. I found that the Optimode tones were recorded at the same level as Avia with some small differences.

1) The subwoofer tone was off by maybe 1/2 to 1 dB (I forget which direction). Not a real big deal since most people tend to adjust the sub to preference anyway. And this gets you in the ballpark.

2) More importantly, the surround tones in Optimode are recorded 2dB too soft. So if you use Optimode when you calibrate, your calibration will set the rear channels (right and left - I don't have a rear center) 2dB too loud. After my original calibration with Optimode I thought the surrounds were a little hot and Avia confirmed this.

But generally speaking you could use Optimode and calibrate:

*Front right, center and left to 75dB

*Subwoofer to 75dB

*Surround right and left to 73dB

and the result should be the same (+/- 1dB) as calibrating with Avia at 75dB.

That's my experience.
 

Duke

Stunt Coordinator
Joined
Aug 8, 1998
Messages
65
the THX optimode test can be different for each disk they are on. They are to set your system for that disk only, they are not a basic setup disk.
 

John H

Second Unit
Joined
Nov 27, 1998
Messages
472
I have balanced my speakers with AVIA to read 75dB on the RS SPL meter.
When using Avia you calibrate at 85dB to achieve reference.

On older released titles with THX Optimode test tones they are title/disc specific. This is suppose to optimize your system for that title.

The newer release titles that I have seen state the THX Optimode test tones are provided for channel identification only and should not be used for balance calibrating.

John
 

Phil Iturralde

Screenwriter
Joined
Oct 7, 1998
Messages
1,892
To quote John Kotches in another thread of yours
When using Avia you calibrate at 85dB to achieve reference.
FYI:

1) Video Essentials is authored @ -30dBFS. VE recommends the Playback SPL = 75 dB (Weight = C / Speed = Slow)

2) AVIA is authored @ -20dBFS. AVIA recommends the Playback SPL = 85 dB (Weight = C / Speed = Slow)

My Volume Control REF Calibration Mark is Identical (12 o'clock position), when REF Calibrating my HT Setup using the two 'recommended' SPLs for each DVD respectively. But for speed, ease and dedicated LFE Test Tones, I primarily use Video Essentials.

NOTE: The THX Optimode is a nice novelty, and if you don't have a REF Calibration DVD like AVIA or VE, use the AV Receiver internal Test Tones @ 75 dB.

Phil
 

shankar

Stunt Coordinator
Joined
Feb 4, 2001
Messages
85
3. Not too certain what you mean.
Since the 12 ft seating position did not seem to work, I moved closer (3 feet from the speakers) and I thought I heard a difference between in phase and out of phase pink noise when testing the phasing between the LF and center. It appeared transposed, in that the out of phase signal seemed to be localized between the speakers. This means that I have to change the polarity of the center channel wiring. Remember I had checked the wiring polarity with AVIA before. With the THX, I now had to reverse that.

BTW, I'm using the optimode from the new Pearl Harbor DVD.
 

SanfordL

Stunt Coordinator
Joined
Mar 1, 2002
Messages
101
Yikes, I thought this was all going to be much easier.

You might check out some other THX disks and make sure the Optimode on Pearl Harbor is correct, because you have to figure that the Avia disk is as it's what the thing was designed for. I have read that Pearl Harbor has some encoding issues, and this might be one?

One other thing, are you using all THX certified equipment? I don't know if that might matter or not, but if your pre-amp or receiver was not THX'd, well, no that doesn't make sense either. I think I will have to defer to a more knowlegable HT guru out there, because there are a lot of folks reading these sites that know a whole lot more about this than me.

Good luck, and let us all know what the solution is.
 

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