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X-Fi and the Elite Pro: SoundBlaster's Return to Greatness

 by Derek Wilson on August 30, 2005 11:59 AM EST
110 Comments | Add A Comment
110 Comments

X-Fi Processing Elements: Exploring the SRC

Sample rate conversion is one of the causes of poor audio reproduction in current sound cards. So, why make such a big deal out of sample rate conversion on the X-Fi? This time, Creative has implemented an SRC that generates very low noise and distortion, and the Audio Ring allows data that doesn't require sample rate conversion to bypass the step altogether. For the conversion of a 997Hz signal from 44.1kHz to 48kHz, the SRC demonstrated -136dB THD+N and +/- 0.00025dB pass-band ripple. Creative says that this is 300 times the quality of the SRC step in previous generation SoundBlaster products. These excellent results allow data to be passed multiple times through the SRC without any significant distortion of the data, making the SRC a key part in effects processing.

Pitch shifting can now easily be done on the SRC. Multitasking the sample rate conversion hardware for effects further allows creative to justify the efforts that they put into its development. One thing that Creative says can be dynamically applied to sound in realtime through the SRC is the Doppler effect. This could allow game designers, for instance, to apply a Doppler effect to all moving sound in a scene relatively easily. Sound synthesis can also use the SRC to change the pitch of a sound easily. The SRC also fits into 3D audio processing.

In pro audio applications, the SRC can be used to avoid the necessity of an external clock for syncing audio signals. Synchronized audio is still possible on X-Fi, but audio from multiple sources can be mixed with very good results using the SRC. As we have said before though, applications that do not require sample rate conversion will be able to bypass the SRC all together.

In order to create such a high quality SRC, Creative created a three-step hybrid filter. First, the sample rate is linearly increased by a factor of 2 using fairly simple math - no complex filters are needed for this step. The next stop along the way to sample rate conversion is a poly-phase FIR filter that up-samples its input to 2*(desired_sample_rate / original_sample_rate). This gives us data with a sample rate that is 4 times the desired sample rate. The final step is to reduce the sample rate by a factor of four (which is also an easy computation). Aside from increasing the quality of the sample rate conversion, increasing the sample rate to 4x the desired final rate also serves as an effective anti-imaging filter. The highest frequency that can be represented in sampled digital audio is half the sample rate (as per Nyquist). Imaging is a "ghost" of the audio signal in the range between the sample rate and half the sample rate. Assisting with anti-imaging is a by-product of the X-Fi SRC.

The above is an example of the SRC employed to convert a 44.1kHz signal to 48kHz. The X-Fi has 256 sample rate converters in its SRC engine. The order of the poly-phase FIR was not given, though Creative maintains that their entire system gives better results than a single order 64 poly-phase FIR filter. The SRC engine also has a tunable cache that can adapt to different latency requirements, as well as its own DMA engine.

The X-Fi Audio Ring: Powerful and Flexible X-Fi Processing Elements: The Quartet DSP
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  • tayhimself - Tuesday, August 30, 2005 - link

    XTREME Yawn!!

    It is Xtreme Fidelity with Xcellent Xquality for XTREME music and XTREME gameZ!!!!
    No thanks! When will this XTREMEly stupid marketing stop??
    I'm still using the nforce2 soundforge because my audigy didnt ship with Creative Mediasource which allows output of music to 5.1. Newer Audigys did ship with MediaSource and could handle 5.1 music output just fine. Needless to say I am XTREMEly pissed and creative and wont be buying something from them again.

  • Googer - Thursday, September 1, 2005 - link

    http://sonicfocus.com/help/help_page.html">http://sonicfocus.com/help/help_page.html

  • dejerez - Wednesday, August 31, 2005 - link

    media source is available for download from creative site. It is a few files all together but this software is for free if you have Audigy. 5.1. upmix option is not in media source but in the card settings that install with the drivers. I had Audigy and used Playcenter and than upgraded for free to Media Source. No problem. I used Audigy with tweaked driver for Audigy 2 to get more features and then eventually bought Audigy 2 ZS and used that with Software availble from their site. I had no problem with an upmix option. I cannot see your point here. Which version of the card do you have?

  • flexy - Tuesday, August 30, 2005 - link

    yeah those "extreme gamez" are actually just TWO, namely doom3 and bf2..which (i THINK) support x-fi....if at all. Was not clear in the review. The point is that they even said they did not hear ANY diff between this and "older" hardware.....

    I think it's ironic that (at elast for gaming and occasional music listening) a $42 Audigy 2 OEM (which has 5.1 output btw) is AS GOOD as a card 10x the money.....and, in all honesty, i do NOT think that my ears are good enough to "notice" a 4db better SNR ratio or similiar nonsense....not to mention someone would have a hard time selling me this card :)

  • DerekWilson - Wednesday, August 31, 2005 - link

    The coloration from the poor frequency response and IMD sweep at 16-bit 44.1kHz really deadens cd auido and mp3s on the Audigy 2 line. Its not about a slightly worse SNR or a little less dynamic range. It's about poor sound reproduction and bad sample rate conversion.

    Of course, gamers won't care as much about this problem. And we can help get around some of the issues by bypassing windows kernel mixer on Audigy hardware.

    I wouldn't buy an X-Fi Elite Pro either. The price point is hard to swallow.

  • dejerez - Wednesday, August 31, 2005 - link

    Sample rate conversion does not seem to be an issue any more, right?
    X-fi audio processor has SRC engine that converts to and from any resolution at 136dB THD+N. Check the review on digit-life. They say
    "Judging from our measurements, the problem with a lot of distortions is a thing of the past now. The 44.1 kHz mode in X-Fi cards is no different from 48 kHz"
    They also compared the quality of the new hardware SRC X-Fi vs the wide-spread real-time SSRC WinAmp plug-in, "notable for its relatively high quality and decent CPU load"
    They conclided by saying
    SRC of the X-Fi outperforms the SSRC plug-in and it causes no distortions - audible or visible on the diagram.

  • xpose - Tuesday, August 30, 2005 - link

    i was so close to first :(

  • vijay333 - Tuesday, August 30, 2005 - link

    Thanks for the review. Was looking into maybe getting one of these soon but I'll stick with onboard for a while until I get one of the Audigy boards.

  • InuYasha - Tuesday, August 30, 2005 - link

    first!

  • Phantronius - Tuesday, August 30, 2005 - link

    1st!!! Yes!!!

    Seriously, looks like I have no reason to part with my Audigy 2 quit yet.
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