Why the DX10/10.1 Radeon tessellator can’t support DX11 tessellation

Illustration courtesy of Emil Persson

No doubt a lot of owners of Radeon HD 2000 up to Radeon HD 4000 series of GPUs are wondering why their cards can’t support the seemingly identical feature called tessellation, which is a big part of the Direct3D 11 spec. Well, it seems like AMD has provided the answer itself.  According to the AMD technical paper Programming for Real-Time Tessellation on GPU the tessellator on the Radeon HD 2000/3000/4000 series is activated through AMD’s own tessellation API interface that works in-conjunction with Direct3D 9/10/10.1. This API however supports up to 15 times amplification, or levels of subdivision of the polygons. The more amplification, the smoother the tessellated polygonal object becomes, eventually becoming spherical.

Video by KhaMichel

The 15 times amplification limit on the AMD API isn’t likely to be arbitrarily set by the engineers at AMD; it probably reflects the maximum capability of the dedicated tessellator featured in the Radeon HD 2000/3000/4000 series. [Update: after this article was published AMD contacted Geeks3D.com and has confirmed that this is indeed a 15x hardware limitation as I have predicted] On the other hand, Direct3D 11 supports up to 64 levels of amplification. Since Direct3D (mostly) dropped cap bits starting from version 10, only Direct3D 11 cards can access all the new features in the Direct3D 11 API. The pre-5000 series cards simply do not meet the minimum amplification capability in the Direct3D 11 spec and therefore cannot use tessellation using this API.

On the other hand, it might be possible that AMD could extend its tessellation API to interface with Direct3D 11, and that remains an avenue to be explored.

P.S. While one might guess that 64x amplification is better than 15x, tessellation still needs to be used in moderation and carefully. As in the words of AMD:

The amplification rate is important because it provides guidelines for the coarse control mesh polygon budget with respect to the desired features in the super high-resolution mesh (also referred to as the “limit surface”). If we want to represent high-frequency features in our high-resolution surface (such as small bumps, warts, wrinkles and bevels), we need to make sure that the coarse mesh has enough polygons to generate positions for these features. Therefore, the higher the amplification rate, the lower the polygon count for our control cage can be.

Creative Inspire T6160 review

With Logitech appearing to be shifting its focus to 2.1 computer speaker systems comes the latest incarnation of Creative’s 5.1 surround sound system for the computer – the Inspire T6160. It features five equally powered satellites rated at 6W RMS (meaning the center channel is not additionally amplified), and one 20W RMS subwoofer. Creative also rates a frequency response of 40Hz – 20kHz and 75db of signal-to-noise ratio. The subwoofer enclosure appears to be constructed from wood and the satellites are encased in plastic material.

The magnetically-shielded satellite speakers each contain a single 2-inch driver with a cone designed to separate mid-tones from the treble. The 5.25-inch subwoofer is of a downward-firing design. The front speaker cables are 1.7 meters long, and the rear speakers cables are 4 meters long. The front cables are long enough but the rear speaker cables require extension cables to be hanged on ceiling corners or on walls.

The speakers come with a volume controller which also acts as an on/off switch. Bass level is located on the back of the subwoofer. The speakers are connected to the computer through three 3.5mm audio connectors. The Now it’s time to put the speakers through its paces.

Sound quality test

Testing was done with the speakers arranged according to the ITU 775 standard (the standard 5.1 speaker arrangement) in a 75cm radius, which is about the typical distance for desktop computer use.

Movies: the T6160 performed exceptionally well in Clint Eastwood’s Letters from Iwo Jima which makes excellent use of surround sound effects to recreate the battlefield atmosphere (no wonder the movie earned the Academy Award for Best Sound Editing). Bass response was very good and detailed at approximately 70% volume level (very ear-deafening), with no noticeable distortion – creating very believable cannon blast sounds. Only when going over this volume level would the bass start to become muffled, but you would need to wear ear protection to listen to this. Particularly impressive are the satellites, with very sharp, rich and clear delineation between mid-tone and treble effects – you can clearly differentiate the multilayered sound effects in the crossfire scenes which was only enhanced by impressive surround effects from the hovering aircraft which were accurately recreated by the rear channel speakers.

When playing Peter Jackson’s The Lord of the Rings: The Return of the King, the T6160 was able to retain the clarity of the background soundtrack even during heavy action scenes, and Nazgûl screeches were very well defined by the satellite speakers – very impressive when you consider the fact that the satellite speakers do not feature a dedicated tweeter. To test channel separation performance, I used George Lucas’ Star Wars Episode I The Phantom Menace’s podracing scene. Even with the volume turned to a very loud 70%, there was very little channel crosstalk detected, and the T6160 delivered some impressive rear surround effects. The transition between the two rear speakers was very smooth, so was the transition from front speakers to the back. There was very little to fault here.

The only real-world problem observed when testing the T6160 is that since the center channel is equally powered as the rest (which is actually ideal), movies with a very large dynamic range will require volume calibration (a boost in volume) to the center channel on the T6160, or a reduction in dynamic range to compensate. Otherwise, dialog from the center channel would often be overwhelmed by sound effects from the left and right speakers. But this is a problem of the sound material, not the speakers.

Distortion: hissing noise from the satellites was detected at all volume levels, although they only become a problem when the volume is set near the maximum. Subwoofer humming noise was low but could be heard with the bass level knob turned up to its maximum. While the subwoofer would distort above 70% volume, it was very hard to make the satellites to clip. In fact, the satellites only clipped when playing synthetic sounds, such as the startup sound of Windows 7′s Minesweeper game, clipping occurred at the 70% volume and above, which should be repeat again is very ear-deafening. Overall, the distortion characteristics were very good in the normal volume levels.

On another note, the subwoofer had no trouble reproducing 20Hz with a volume of approximately 33%.

Summary

The T6160 exhibits very good sound quality. At a retail price of AUD $118.14/USD $79.99 (at the time of writing you can get them for AUD $79 at MSY), it is a great choice for those who are just starting out with surround sound for the computer. If you have RCA extension cables, it would make for an inexpensive small home theatre sound system too – the speakers have enough power and clarity for a sound space radius of up to 3 meters.

Update: added subwoofer image

How to pass the Driver Qualification Test

Recently I took the Driver Qualification Test (for drivers in New South Wales, Australia) and like many people I wasn’t exactly sure at first how to be fully prepared for it. Having done it here are some quick tips to help you ready for it.

1. Know your Drivers Qualification Test handbook thoroughly

In the first part of the test, there are statistical and numerical information to be call upon in the multiple choice quiz. Pay particular attention to the summaries contained in each section of the test handbook.

2. Practice hazard perception tests

There are a few excellent websites that provide sample hazard perception tests. Even though they aren’t the same as the ones RTA use they serve as a good guide to it.

• Bill Plant Hazard Perception Test (UK)
• Government of Western Australia Department of Transport

3. Wear the supplied headphones for the sound feature

You can improve your concentration and lessen the chance of misunderstanding when you can hear the questions and answers spoken out to you. Ask the staff before you start the test if you can’t find a headset next to the computer.

4. Take the two practice hazard perception questions, repeat them if necessary

When you get to the second part of the test, you’ll be given the chance to practice some of the video hazard perception test questions. Always take this opportunity to familiarize yourself with the sensitivity and timing of the tap responses that the test requires.

5. Don’t tap on the screen too much on the hazard perception test

Pretty obvious. You only need to tap once for each hazard you have identified.

6. Read carefully what the driver intends to do in the hazard perception questions, reread if necessary

Last but not least, when you get to actually answer the real hazard perception questions, make sure you know what the question is asking. It could be asking you to tap when to slow down, when to turn, or when to overtake. But you won’t get the taps right if you don’t know what you as the driver want to do.