X-Fi Processing Elements: The Quartet DSP

Audio effects and processing can be done on a CPU. The latest audio solutions from Intel employ software from Sonic Focus that performs audio processing without the aid of dedicated hardware. If an end user wishes to enable advanced filtering or processing features, the Creative X-Fi has the advantage of being able to perform these tasks without tasking the CPU (thereby freeing up resources for other applications).

As is often the case, a general purpose CPU is not the most efficient hardware for the job. The Quartet DSP is able to make quick and efficient work of audio data. As mentioned before, the Quartet is made up of 4 independent two-issue SIMD engines, which Creative calls a TIMD architecture for Thread Interleaved and Multiple Data. The configuration of the SIMD paths in Quartet lend themselves well to audio processing.

Creative didn't tell us how wide the data path is down each SIMD pipe, but Quartet is able to handle either integer or floating point data, making it more flexible than DSPs used on older Creative parts. Special instructions allow differing operations to be performed on SIMD data to enable more efficient audio processing. For instance, the FADDSUB2 instruction performs an add-on-one data path and a subtract on another. The DSP is also able to perform complex floating point math with the real and complex results completing in different paths.

In traditional DSP architectures, raw speed often wins out over programmability. Tradeoffs are always necessary, but the Quartet offers a good balance. The result of one instruction can be used in the next with no stalls or reordering necessary and any instruction can be performed after any other instruction without any conflict. Also, any register can be used as any operand in any instruction. While we don't have all the details on the hardware, a high level language compiler could easily target and optimize for this architecture.

At this point, an easy to develop and efficient compiler only really helps Creative write driver and feature code more easily. It could be possible for Creative to allow developers access to their compiler in order to develop specialized DSP code. We don't know if Creative will actually pursue this in the future, but the option is there should they choose to do so.

To sum up the capabilities of the Quartet DSP, we have this list of features:
  • 2 SIMD units per each of 4 simultaneous threads
  • fixed and floating point data supported
  • 235 opcodes
  • up to 1200 MIPS
  • can perform up to 4 moves per instruction
  • easy to compile and optimize
Bringing the entire Audio Ring architecture together, Creative has quite a powerful solution that can handle lots of quick and efficient processing. Multiple audio streams with multiple sample rates can be floating around, being processed and reprocessed with high efficiency and low latency. This gives Creative a good deal of freedom in how heavily they can process audio without needing any assistance from the CPU.

X-Fi Processing Elements: Exploring the SRC New Features, Possibilities, and Modes
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  • Fricardo - Saturday, October 29, 2005 - link

    I would really like to see performance numbers on the cheaper x-fi components. Reply
  • flachschippe - Monday, October 24, 2005 - link

    quote:

    the Quartet is made up of 4 independent two-issue SIMD engines

    "Thread-Interleaved" could also mean simply multithreading, but on a single processor ("engine").
    Reply
  • Gooberslot - Thursday, September 01, 2005 - link

    Am I wrong in assuming that having high stereo crosstalk in the upper ranges is worse than having it in the lower ranges? If not then this X-fi is junk because that crosstalk is way too high. Reply
  • ceefka - Thursday, September 01, 2005 - link

    You're right: the whole idea behind a 5.1 setup. With most modern music however a lot of high frequencies aren't even panned in a distinctive direction. Reply
  • Anton74 - Wednesday, August 31, 2005 - link

    What's the resolution of the ADC? Is it the same for the various X-Fi cards available at the moment? Reply
  • MrCoyote - Wednesday, August 31, 2005 - link

    Creative still hasn't got it right. The chip resamples all audio, just like the Audigy series. This is no good for musicians and amateurs that want to use it to record audio. If you set your audio software to record 24bit 96KHz, it will downsample to 16bit 48KHz, and then upsample output back to 96KHz. Cheaper audio cards from M-Audio can do true sampling faithfully. Why can't Creative get it right?

    Sorry, but I'm passing it up and sticking with M-Audio. I may lose a few FPS and not have EAX3, but true, faithful sampling is what I also need for recording. I don't just play games. Creative thinks audio cards are only good for games, not recording. I'm not wasting money to buy two different audio cards.
    Reply
  • dejerez - Wednesday, August 31, 2005 - link

    What product do you refer to? X-Fi does not need to down- or upsample. Everybody has their preferences but being M-Audio advocate does not mean you do not have to read review of the product you are posting comments about. X-Fi's clock works at the speed of your choice. And if you WANT to use sample rate conversion this has been vastly improved. That is the only card on the market that does distortion-free SRC which is great if you want to mix sounds from sources recorded at differnet sampling rates. Are you musician? I wish you were because you are not in position to appreciate how much this card can help a recordist or sound engineer... Reply
  • DerekWilson - Wednesday, August 31, 2005 - link

    dejerez is right -- you can set the card to internally sample everything at 96kHz.

    I'll also agree that mixing sources of different samplerates with no distortion and no conversion necessary is a nice thing. But locking samplerate is also important in the current landscape of audio software.
    Reply
  • mindless1 - Thursday, September 01, 2005 - link

    I'm not so sure you're correct here. Setting it to "sample everything at 96Hz" may be exactly what causes the resampling that audiophiles want to avoid. Internal sampling rate is a variable any card could do with software alone, but I/O sampling rate is not.

    It also appears to have NO 44.1 crystal, meaning it can't even play back an audio CD properly without resampling it.
    Reply
  • Somerset - Tuesday, September 06, 2005 - link

    You can set X-Fi to play back audio CDs at 44.1kHz without any resampling. In the Audio Creation mode, you can easily set the master clock to 44.1kHz if desired. On the other hand, resampling is no longer a negative with X-Fi as all audio test graphs clearly show that X-Fi's resampling produces a very clean signal. Resampling should no longer be considered a weakness of X-Fi. Reply

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