CurtPalme.com Home Theater Forum

[gjaky]

[CIR Engineering]

[Hulio]

Yepp, so true guys. My bad....

[nidi]

here's something I've been saving.

originally from Scott (TSE):


1080P 1920x817 72Hz


TSE response:

This is probably not exactly what you are asking for but if you follow these guides the projector will be happy.

Keep vertical blanking about 5% of the frame time.

1/72Hz = 13.9ms

13.9ms x 0.05 = 700us

So that leaves 95% of the frame time to display 817 lines.

1/72Hz x 0.95 = 13.2ms

13.2ms/817 lines = 16.15us for each displayed line. Horizontal frequency will be 1/16.15us or 61.92KHz.

Allow 20 to 25% of the line time for horizontal blanking. Analog (CRT) displays need their retrace time.

So, 16.15us x 0.25 = 4.04us or 16.15us x 0.2 = 3.23us
Less blanking time means lower pixel clock if projector can retrace in time.

With 25% blanking there is 12.11us to display 1920 pixels. The pixel time will be 12.11us/1920 or 6.31ns. The pixel clock will have to be 1/6.31ns or 158.5MHz.

With 20% blanking there is 12.92us to display 1920 pixels. The pixel time is 6.73ns. 1/6.73ns means pixel clock is 148.6MHz.

If the video source has a max pixel clock of 150MHz the blanking times can make a big difference.

This usually works. Allow 20% of blanking time (h or v) for front porch. Leave 25 or 30% for the sync time and the remaining 50% for back porch. The CRT projectors should like it.

Sorry if I'm telling you stuff that you already know and I'm not sure that this even answers your original question.

Scott

1920x1080p@72Hz will need pixel clock of 179.6MHz if set for minimum blanking times of the projector (400us v retrace/1.8us h retrace).

67Hz is fastest refresh rate that runs w/ pixel clock under 165MHz.

The projector's retrace times are already very short. The designers put alot of effort into getting where it is. There is not really much that can be done to make them shorter.

Scott




The guides that I wrote about should still hold true if using lines and pixels to set the video source.

Use about 5% of frame time for v blanking so 817 lines are 95% of the total lines or (817/0.95)x1 = 860 total lines.

Use 20% of the total line time for h blanking so 1920 pixels are 80% of the total pixels or (1920/0.8)x1 = 2400 total pixels.

V blanking is 860 total lines - 817 displayed lines or 43 lines.

H blanking is 2400 total pixels - 1920 displayed pixels or 480 pixels.

25% of blanking time for front porch gives:

0.25 x 43 lines = 10.75 round up or down to 10 or 11 lines.
0.25 x 480 pixels = 120 pixels.

25% of blanking time for sync gives:

10 or 11 lines for v sync.
120 pixels for h sync.

Use the rest of blanking for back porch:

43 lines - (fp + vs) = bp
480 pixels - (fp + hs) = bp

Note: fp + vs + bp should add up to total blanking lines. It might freak out video source if it doesn't. Same with blanking pixels = fp + hs + bp.

Now, there might be limitations on minimum h sync width like with Marquee projector. H sync minimum width is 1us. The above example will give h sync time = 808ns. Not ideal.

(1/72)/860 = total line time = 16.15us
16.15us x 0.2 = 3.23us ( h blank time)
3.23us/480 pixels = 6.73ns
1us/6.73ns = 148.6 pixels. 148 pixels is close enough. Split the remaining h blank pixels between fp and bp. Keep blanking pixels at 480 = fp +hs + bp.

So:

Refresh or vert freq = 72Hz

total lines = 860
displayed lines = 817
vfp = 10
vsw = 11
vbp = 22

total pixels = 2400
displayed pixels = 1920
hfp = 90
hsw = 148
hbp = 242

Should work if video source will accept the numbers. The projector will certainly like it.

Scott

[Hulio]

Thanks Michael. No, i didn't tried those timings on 817p yet. It sounds good.
In the mean time, i will also order a ViewHD splitter. Sometimes i loose sync.

[Francisco]

"If" your Crystalio is failing and you would like to use 1080p@72hz consider HD-Fury 3d in place of the crystalio. So source > hdmi > in HD-Fury (scaling 1080p@24hz to 1080p@72hz) hdmi out > hdmi in to the moome.

Use the HD-Fury as a scaler, you can adjust porch timings etc.

I could never get the C2 to do full 1080p@72hz with Barco 909 friendly porch timming. Pixelclock always turned out to be too high for the C2. Giving no image or same problems you are having.

[Hulio]

Thanks for the advice Francisco. It's a damn shame that the max. pixelclock on C2 is only 150Mhz. I really like the GUI and user-frendlyness of the scaler. Right now, i am waiting for a HDView HDMI-splitter ( as i have sometimes handshake issues ). I haven't done too much with my Barco this days, too busy with other things.
However, i did tried 1920x817P@72Hz like Nidi sugested. For some reason, without much luck. Also, no improvements with different short HDMI cables.
I will try the 3DFury too, if i find a second-hand one. If it works @72Hz but i have to trade in a lot of sharpness, i might stay with 1080P@60Hz from the scaler.
Have a very happy new year guys, with a lot of CRT fun.