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high freq roll off. (1 Viewer)

snivit

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Bob Rose
Hi,
I am a long time audiophile. I have (under spousal duress) entered the home theatre arena. The big issue for me is the high end roll off in 5.1 . It sound decent but i really miss the high end extension. When i viewed dvd's on my two channel system ,there was an awsome sense of reality. Now it sounds like a nice theatre. Is there something i am missing in the set up options or am i stuck with this roll off.
I know why the roll off was designed in, but on a good system it is a degrade in my opinion. I want real, not two thirds back in the theatre sound !
Help !
Thank you all.
 

JohnRice

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The rolloff is only in the surround channels. There should be absolutely no fidelity difference between listening to a DVD in 2 channel and the same DVD in 5.1. Did you calibrate your 5.1 system with a sound pressure meter and a calibration disc like Video Essentials? A lot of people just hook everything up and expect it to automatically work, which it doesn't.
 

sptrout

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I thought that the Dolby frequency response spec was 20Hz - 20kHz for all 5 main channels, and 20-120Hz for the LFE channel. Are you saying that this is not correct or that the response (rolloff) above 20kHz is different for the surround channels vs. the main channels?
 

JohnRice

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Well, now I forget which is which. This is coming from the vitriolic bashing between DTS and DD a few years back. They both need to use some method to reduce the overall bitrate and one rolls off the frequency of the surrounds, yet keeps them fully discrete. The other runs them at full frequency range, but blends the two channels together at higher frequencies. I don't remember which is which.
 

Lew Crippen

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Actually with the newer, lossless codes, such things don’t matter at all.

Of course we can all anticipate true believers promoting one lossless format over another.
 

snivit

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Thanks for the response. I have designed speakers for years and years. I did a sweep with pink noise and my R.T.A. and found a roll off that starts at 2k and continues out. This is a known design for me and should be very flat. Off axis taken into consideration. I am pleased to hear that it should be flat. I wonder if something is wrong with the receiver or dvd player. The roll off almost reminded me of C.D. de-emphisis being on when it shouldn't be. Right now i'm at a loss to explain it. I do wonder if there is some option in the setup of the receiver that i missed somehow.
If anyone has an idea where to look, please let me know. If not, I will follow up when it gets sorted out just in case anyone else is ever baffled by this.
Thanks again for the response.
 

sptrout

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DD or DTS 5.1 should not be rolling off anywhere near 2KHz. I assume that you have a new AVR since you are new to the home theatre world. Do other audio inputs roll off or is it just 5.1 from the DVD player? My guess is that the DVD player is OK since it just passes the digital audio track to the AVR for processing; I don't see level issues here. Something must be wrong in the AVR, but I cannot image a setting that would have such a damaging impact on frequency response. You may want to list the model numbers of your equipment then someone may be able to provide more insight. It is difficult to make suggestions without knowing exactly what equipment you have and how everything is interconnected.
 

JohnRice

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True, but those formats are far from being the norm at this point.
 

snivit

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My receiver is a jvc digital varible bias amp.7.1 ex, dts....etc. Tripath class t digital amps i hope , but haven't looked yet. I'm running a 5.1 setup. I bought an upsampling dvd (Samsung) connected to coaxial output bitstream. I have an older denon that i tried and got close to the same results. I also tried to shut off the surround mode and run stereo through it and it spit out the same response. I wonder if it is stuck in a Pro logic response mode?
FRRRUUSSSTRATING!!!!
 

snivit

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Since my last post I tried the analog outputs from my dvd and it was very flat. Plenty of high freq. I tried another player and had the same result. In digital output to the receiver, it rolls off on both players.
Is there anyone out there that has actually swept the response in the dig. out with pink noise? Is it my receiver or Dolby?
Thank you for any input to this issue.
 

troy evans

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Bob, what did you set the bass management cut-off freq. in your receiver to for each speaker? What did you balance the levels of all your speakers to 75db,85db?
 

Jeff Gatie

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If you were only using analog before, check the DD/DTS settings for your DVD player(s). Usually a player will output a Pro-Logic downmix by default, which will result in a rolloff in the surrounds due to the matrixing. This rolloff will not be present in the analog 2 channel, since it is not matrixed. Set DD and/or DTS to "On" (or "Bitstream") in the setup menu and re-test. There should be no rolloff if you are truly hearing the DD/DTS stream
 

pankarty

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snivit

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Found it!
The dvd player had the pcm downsampling on. The system now measures very flat
Thanks all....
 

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