DLP noob-some comments and questions...

Discussion in 'Displays' started by christopher-h, Nov 21, 2005.

  1. christopher-h

    christopher-h Auditioning

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    I just got my first big screen TV. It's an Akai PT46DL10, 46" DLP. Before this I had a 34" Philips direct view CRT HDTV.

    I absolutely LOVE most things about this DLP-no geometric distortion, no blooming whites or black levels changing depending on what's being displayed, rich natural colors, razor sharp images, bright picture and WIIIIDE viewing angle.

    Having watched nothing but CRT's before this I wish the DLP had richer blacks, but the benefits more than make up for this. My major concen with this new DLP is how it displays dark grays. When I am sitting back on couch watching it the grays look good(not as much shadow detail as CRT, but still good). At close distance though, I can see that the grays are filled with noise, slightly greenish tinted pixels moving around. This noise is what actually makes the dark grays look lighter than black. The more noise, the lighter the shade of gray up to a certain point.

    I have not watched hi-def video yet, but this noise shows up on all things I have tested with, 2 DVD players and an XBOX in both 480i and 480p on multiple component video cables. I just did some calibration with Video Essentials and got the brightness, shapness, color and tint set but I'm not sure what the contrast should be set to since the patterns for this test never showed distortion.

    Once again this is not noticeable if I am more than a couple feet away from the TV, so I don't really mind it except for the lack of definition in dark shadows. Is this how grays usually look on DLP or could I have a defective TV? I am kind of concerned about this since it was an open box model. Also does anyone know how to get into the service menu for this TV?

    Thanks, Chris
     
  2. Philip Hamm

    Philip Hamm Lead Actor

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    Do you know with 100% certainty that your source is purely black and white / grayscale?
     
  3. ChrisWiggles

    ChrisWiggles Producer

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    the noise you are observing in dark scenes is dithering, and is inherent to the PWM behavior of DMD chips.

    To calibrate your DLP, use DVE and for white level use the ramps pattern. Your goal is to maximize both white and black level as much as possible within the capable range of your display. At the extremes, DLPs will either begin to clip whites, or will start to colorshift. The clipping is more obvious, the colorshifting is more subtle to see. Ramp your white level up to maximum and go up and down and look closely at the bars pattern for clipping or colorshifting at the brightest portions of the patten. Keep in mind that other components in the system may already be clipping whites, reference white is marked in this pattern by the dots (and the same for video black) but there should be a brighter white step, and it should continue to ramp up beyond reference white to the edge of the pattern. When you observe clipping or colorshifting, set your white level as high as possible to JUST below this point. Note that this is for calibating a digital display, and NOT a CRT display which is different.

    For black level, the dithering noise you see is negative and inherent to DLP, however it also allows you to find the black level of the display with great accuracy. When adjusting black level, pull up any DVE pattern with a black background, a PLUGE pattern with a low % center bar is a great choice. You should see dithering in the bars that are above black, and if your black level is elevated you will also see dithering in the black background. Also check to see if the BTB bar is present or clipped. Using the black background, lower your black level and observe the dithering closely at the screen, and at some point you will see the dithering vanish. This is your black point of the display. Align black in the pattern to this point.

    You may need to go back and check white level as the controls may interact. in this way you can maximize the available contrast range of your display for the best picture that your display is capable of.
     
  4. christopher-h

    christopher-h Auditioning

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    Great tips. I just got DVE and am going to do some calibration tonight or tomorrow, hopefully I can pull some more shadow detail out of my DLP.

    I will also be setting up my audio receiver tomorrow. From what I have seen in Video Essentials and what I have read, it appears that the only tool I need for the sound calibration is an SPL meter which I will be picking up tomorrow. Any pointers for sound calibration?
     
  5. Philip Hamm

    Philip Hamm Lead Actor

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    If you're using a Radio Shack SPL meter, you need to know that the sensitivity to the sub tone frequency is going to be about 3dB down. If the other channels are set to 0dB on the meter, set the sub to -3dB on the meter because there's a rolloff on the bass frequencies the microphone on the SPL meter can handle.
     

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