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Old 18th March 2014, 18:11   #1  |  Link
Nachbar
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Join Date: Jun 2012
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CVT Reduced Blank (CVT-RB) loses HD audio capability

I am losing the capability of playing HD audio formats via HDMI when I use my television. This only occurs when I set my television to "CVT Reduced Blank" in the custom resolution option. I have to use that setting to get full 1080p to work correctly otherwise I have an overscan issue. However if I instead use the automatic setting and then resize the desktop to 1824x1026 to correct the overscan I then get my HD audio capability back.

My card is a EVGA Geforce 560 Ti 1GB which has 2 DVI slots and a mini HDMI slot. I tried all the slots using the supplied adapters that came with my card but to no avail.

To clarify what HD audio I am losing:
CVT Reduced Blank @ 1080p: DTS, DD+, DD @ a max of 24-bit, 96khz
Resized desktop @ 1824x1026p: DTS, DD+, DTS-HD, Dolby TrueHD, DD @ a max of 24-bit, 192khz

I have a MSI Geforce 650 in my other computer that I am going to try later tonight to see if that works. I would really like to be able to use 1080p while retaining HD audio capability over HDMI. I am open to any and all ideas on how to make this work.

System specs:
EVGA Geforce 560 Ti 1Gb with 335.23 WHQL drivers
Intel Core i5-3570K 3.4GHz Quad-Core
Asus P8Z77-V PRO ATX LGA1155
Pioneer VSX 1021-K receiver -> Magnavox 40mf430b/f7
Acer H233H Monitor
Windows 7 SP1 64-bit
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Old 19th March 2014, 07:17   #2  |  Link
Nachbar
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Update: I contacted EVGA and they suggested trying another card and disabling other audio devices. I used a Galaxy GTX 650 Ti and observed the same problem. Disabling other audio devices and rebooting didn't solve the problem either. I can only conclude it must be a driver problem. I could try downgrading to an older drive to see if it helps. If you guys have any suggestions on anything else to try or what specific drivers I should test with please let me know.
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Old 25th March 2014, 08:29   #3  |  Link
Asmodian
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Oddly this sounds like a bandwidth problem to me, with lower resolution (bandwidth) video you can use higher bandwidth audio. HDMI does have bandwidth limitations, I assume you are using 60 Hz; maybe test the theory with 30 Hz? It could be the cable, the receiver (I doubt it), or the video card (drivers or hardware) as both your cards a fairly similar. Do you have another receiver or something to test that end? How about another cable as unlikely at it seems?

Have you tried custom super minimal timings? Start with CVT Reduced Blank but set the front porch and sync width lower (maybe 2, 2 for Vertical?), you can also try lowering total pixels but not too much. Most devices don't break if you give them bad timings, they just do not display an image.
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Old 25th March 2014, 16:27   #4  |  Link
Nachbar
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Thanks for the suggestion Asmodian. Actually raising the timings fixed the problem. I learned that audio is tied into the pixel clock rate and raising the total pixels raises the rate. So basically what I did was set it to cvt-rb and then raised the pixel total until it worked. Right now it is set to 2088 - 1111 which translates to 139.1861Mhz. If I start to go higher i run into issues like the monitor losing signal and overscan coming back. The default for CVT-RB is 2080 - 1111 at 138.6528 so it only raised it by a little over 0.5 Mhz.
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Old 27th March 2014, 05:12   #5  |  Link
Asmodian
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Glad you figured it out but that is very odd. So you had to find the sweet spot between the monitor switching to overscan mode and having too low of a pixel clock to send the audio? I wonder how the audio is attached to the signal and why it cares what the pixel clock is? What would it do with a 720p signal, no HD audio either?

Thanks for letting us know what did it, I learn something new everyday here.
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