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One of the drawbacks of the GPUs built into the Clarkdale/Arrandales CPUs and the Sandy Bridge CPUs was the lack of 23.976 Hz for matching the source frame rate of many videos. Combined with the lack of reliable support for open source software, this has often pushed users to opt for a discrete HTPC GPU.

Ideally, a GPU should be capable of the following refresh rates at the minimum:

  1. 23.976 Hz
  2. 24 Hz
  3. 25 Hz
  4. 29.97 Hz
  5. 30 Hz
  6. 50 Hz
  7. 59.94 Hz
  8. 60 Hz

Some users demand integral multiples of 23.976 / 24 Hz because they result in a smoother desktop experience, while also making sure that the source and display refresh rates are still matched without repeated or dropped frames.

However, being in the US (NTSC land), we are looking at the minimum necessary subset here, namely, support for the following:

  1. 23.976 Hz for 23.976 fps source material
  2. 24 Hz for 24 fps source material
  3. 59.94 Hz for 59.94 fps source material

We have observed that the refresh rate is heavily dependent on the AV components in the setup (a card which provided perfect 23.976 Hz in my setup performed quite differently in another). In order to keep the conditions same for all the contenders, the custom refresh rates were tested with the HDMI output of the card connected to an Onkyo TX-SR606 and then onto a Toshiba Regza 37" 1080p TV. The Toshiba TV model is indeed capable of displaying 24p material.

GT 430:

The NVIDIA Control Panel provided a 23 Hz option by default when connected in the test setup. This is obviously coming from the EDID information. Setting the refresh rate to 23 Hz and playing back a 23.976 fps video resulted in the following:

Note that the playback frame rate locks on to 23.971 fps, and the display refresh rate also loosely locks on to 23.971 Hz. Unfortunately, this is only slightly better than the 24 Hz lock that Intel provides for the 23 Hz setting. With this, one can expect a dropped frame every 200 seconds.

Fortunately, NVIDIA provides us with a way to create custom resolutions using the NVIDIA Control Panel, as in the gallery below.

The display mode refresh rate should be set to 23 Hz, and the Timing parameters need to be tweaked manually (altering the refresh rate to change the pixel clock). This is more of a trial and error process (setting the refresh rate to 23.976 as in the gallery below didn't necessarily deliver the 23.976 frame lock and refresh rate during media playback). With a custom resolution setup, we are able to get the playback frame rate to lock at 23.976.

The display refresh rate oscillates a little around this value, but, in all probability, averages out over time. We do not see any dropped or repeated frames.

Moving on to the 24 Hz setting (needed for 24 fps files, common in a lot of European Blu-rays), we find that it works without the need for much tweaking.

Playback locks at 24 fps, and the refresh rate oscillates around this value with very little deviation.

The default NTSC refresh rate (59.94 Hz) works in a manner similar to the 24 Hz setting, as is evident in the gallery below.

MSI GT 520:

With respect to custom refresh rates, the GT 520 is very similar to the GT 430. The 23 Hz setting, at default, had the same issues as the GT 430, but nothing that a little tweaking didn't fix. The gallery below shows the behavior with the default 23 Hz setting:

After setting up a custom resolution, we get the following:

The 24 Hz setting, at default, showed a slight issue with the playback frame rate locking at 24.001 Hz. This would imply a repeated frame every 1000 seconds (~17 minutes).

This can probably be fixed by altering the timing parameters for the 24 Hz setting, but we didn't take that trouble.

Setting up NTSC refresh rates with the 59 Hz native setting gave us the following results, similar to the issue we had with 24 Hz setting.

DDR3 and GDDR5 based 6450 :

We didn't find any difference between the two versions of the 6450 that we tested with respect to refresh rate handling. In this section, we will present screenshots from the GDDR5 based 6450.

Catalyst Control Center automatically enables the 23 and 24 Hz settings in the drop down box for refresh rates by recognizing the EDID information. How well do these settings work? A look at the gallery below shows that the behavior is better than Intel's and NVIDIA's native offerings. However, there is still the issue that the play back frame rate locks to 23.977 fps / 24.001 fps. The refresh rate is not exactly 23.977 either, but mostly below that. All in all, this is not the ideal 23.976 Hz, but something that the 'set-it-and-forget-it' crowd might be OK with.

We didn't get a chance to test the 59.94 Hz settings for videos, because the 6450s' way of playing back 1080p60 videos was to present a slideshow. A brief look at the gallery below reveals the issue:

There is a little bit more coverage about this in the 'ESVP on the 6450s' section.

Sapphire 6570:

While the 6450 was only slightly off from the required 23.976 and 24 Hz settings, the Sapphire 6570 took a little more liberty. 23 Hz gave us 23.978 Hz and 24 Hz gave us 24.002 Hz, resulting in repeated frames every 500 seconds.

The 59 Hz setting for the 6570 gave us 59.946 instead of 59.94, which eventually results in a repeated frame every 167 seconds (~3 minutes).

The takeaway from this section is that none of the GPUs can claim to do fully perfect 23.976 Hz refresh rates. With luck, the ATI card in a particular setup may be able to provide the perfect refresh rate. After all, they came very close to the required settings in our testbed. The NVIDIA cards, at default, are probably going to be always off. However, for the advanced users, there are some avenues available to obtain the required display refresh rate. Unfortunately, there is no way I am aware of to feed custom refresh rates in the Catalyst Control Center.

Before I started the review, it was my opinion that AMD is much better at native refresh rates compared to NVIDIA. After putting the various cards through the paces, I am forced to reconsider. AMD may work well for the average HTPC user. For the more demanding ones, it looks like NVIDIA is the winner in this area because of the ability to create custom resolutions.

HQV 2.0 Benchmarking Cadence Detection : Clearing the Confusion
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  • enki - Monday, June 13, 2011 - link

    How about a short conclusion section for those who just use a Windows 7 box with a Ceton tuner card to watch hdtv in Windows Media Center? (i.e. will just be playing back WTV files recorded directly on the box)

    What provides the best quality output?

    What can stream better then stereo over HDMI? On my old 3400 ATI card it either streams the Dolby Digital directly (the computer doesn't do any processing of the audio) or can output stereo (doesn't think there can be more then 2 speakers connected)

    Thanks
    Reply
  • BernardP - Monday, June 13, 2011 - link

    The inability to create and scale custom resolutions within AMD graphics drivers is, for me, a deal-breaker that keeps me from even considering AMD graphics. It will also keep me from Llano, Trinity and future AMD Fusion APU's. I'll stay with NVidia as long as they keep allowing for custom resolutions.

    My older eyes are grateful for the custom 1536 X 960 desktop resolution on my 24 inch 16:10 monitor. I couldn't create this resolution with AMD graphics drivers.
    Reply
  • bobbozzo - Tuesday, June 14, 2011 - link

    In your case, you should just increase the size of the fonts and widgets instead of lowering the screen res. Reply
  • Assimilator87 - Tuesday, June 14, 2011 - link

    I wish there was a section dedicated to the silent stream bug. I have a GTX 470 hooked up to an Onkyo TX-SR805 and this issue is driving me insane. For instance, does this issue only plague certain cards or do all nVidia suffer from it? I was hoping the latest WHQL driver (275.33) would fix this, but sadly, no. Otherwise, the article was amazing and I'll definitely have to check out LAV Splitter. Reply
  • ganeshts - Tuesday, June 14, 2011 - link

    The problem with the silent stream bug is that one driver version has it, the next one doesn't and then the next release brings it back. It is hard to pinpoint where the issue is.

    Amongst our candidates, even with the same driver release, the GT 520 had the bug, but the GT 430 didn't. I am quite confident that the GT 520 issue will get resolved in a future update, but then, I can just hope that it doesn't break the GT 430.
    Reply
  • JoeHH - Tuesday, June 14, 2011 - link

    This is simply one of the best articles I have ever seen about HTPC. Congrats Ganesh and thank you. Very informative and useful. Reply
  • bobbozzo - Tuesday, June 14, 2011 - link

    Hi, Can you please compare hardware de-intelacing, etc., vs software?

    e.g. many players/codecs can do de-interlacing, de-noise, etc. in software, using the CPU.

    How does this compare with a hardware implementation?

    thanks
    Reply
  • ganeshts - Tuesday, June 14, 2011 - link

    This is a good suggestion. Let me try that out in the next HTPC / GPU piece. Reply
  • CiNcH - Wednesday, June 15, 2011 - link

    Hey guys,

    here is how I understand the refresh rate issue. It does not matter weather it is 0.005 Hz off. You can't calculate frame drops/repeats from that. In DirectShow, frames are scheduled with the graph reference clock. So the real problem is how much the clock which the VSync is based on and the reference clock in the DirectShow graph drift from each other. And here comes ReClock into play. It derives the DirectShow graph clock from the VSync, i.e. synchronizes the two. So it does not matter weather your VSync is off as long as playback speed is adjusted accordingly. A problem here is synchronizing audio which is not too easy if you bitstream it...
    Reply
  • NikosD - Thursday, June 16, 2011 - link

    Nice guide but you missed something.
    It's called PotPlayer, it's free and has built-in almost everything.
    CPU & DXVA (partial, full) codecs and splitters for almost every container and every video file out there.
    The same is true for audio, too.
    It has even Pass through (S/PDIF, HDMI) for AC3/TrueHD/DTS, DTS-HD. Only EAC3 is not working.
    It has also support for madVR and a unique DXVA-renderless mode which combines DXVA & madVR!
    I think it's close to perfect!
    BTW, in the article says that there is no free audio decoder for DTS, DTS-HD.
    That's not correct.
    FFDShow is capable of decoding and pass through (S/PDIF, HDMI) both DTS and DTS-HD.
    And PotPlayer of course!
    Reply

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