Discrete HTPC GPU Shootoutby Ganesh T S on June 12, 2011 10:30 PM EST
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:
- 23.976 Hz
- 24 Hz
- 25 Hz
- 29.97 Hz
- 30 Hz
- 50 Hz
- 59.94 Hz
- 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:
- 23.976 Hz for 23.976 fps source material
- 24 Hz for 24 fps source material
- 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.
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.
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.