X-Fi and the Elite Pro: SoundBlaster's Return to Greatness
by Derek Wilson on August 30, 2005 11:59 AM EST- Posted in
- Smartphones
- Mobile
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.
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Fricardo - Saturday, October 29, 2005 - link
I would really like to see performance numbers on the cheaper x-fi components.flachschippe - Monday, October 24, 2005 - link
"Thread-Interleaved" could also mean simply multithreading, but on a single processor ("engine").
Gooberslot - Thursday, September 1, 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.ceefka - Thursday, September 1, 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.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?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.
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...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.
mindless1 - Thursday, September 1, 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.
Somerset - Tuesday, September 6, 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.