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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SDA - Wednesday, August 31, 2005 - link
>>For listening, I generally stick with my Sony MDR-7509 headset. I also have the Sennheiser HD580 that I use to audition sound hardware. The reason I stick with the Sony gear for general listening is due to my environment. I can turn everything off when I need to do a noise test or listen closely to something, but the lab with all the computers and workstations running is not a quiet environment. I realize that open air headests will reproduce (especially) the low end in a more appropraite manner, so I do listen with them, but I know the sound a little better on the MDR-7509s as I've been using them for a long time. >>Are either of those headphones being amplified? If not, you are probably putting unfair stress on the sound card's line out, and should at least compare with and without an amp (lots of sound devices sound great if not under undue stress). Also, consider getting monitor speakers to test surround sound output.. old Minimus-7s will do if you're on that tight of a budget (no bass whatsoever, but surprisingly neutral midrange and treble for small bucks and a small room), otherwise look around.
>>I am planning on picking up the HD650 as I've heard great things about them. >>
Enh, they're not different enough from the HD580 to warrant buying if you're looking for sound test gear. Get something with a different flavor first (Grado SR-225 or Alessandro MS-2 for high-current low-impedance rock phones, AKG K501 for analytical ridiculously inefficient mid-impedance phones), and get a reasonably good amplifier (no need for audiophile BS, just something with enough balls to run a K501).
>>Doing something like a double blind subjective study on audio is difficult. People that don't know how to listen won't be any help because even if they hear a difference they won't know how to describe it very well. People who do know what they are talking about are hard to come by in volume. Don't get me wrong, we'd love to do something like this. But we just don't have any idea how to work out the logistics. Suggestions are welcome. >>
Find three different people who know what they're talking about and aren't slaves to the placebo effect. Have them test the gear in a double-blind setting.
More specific advice... look for musicians. Especially look for musicians for testing songs heavy on specific instruments: someone who plays, say, the violin will know exactly what a violin will sound.
>>Also, I appreciate the suggestion to avoid general statements about the goodness of something. It is a good suggestion even in cases where we know everything about everything in detail. There are always surprises and erring on the side of caution is the best way to go. We will be more careful in the future. >>
And, fwiw, I appreciate the maturity and responsibility one gets from AT editors. (Yes, I can give compliments too!)
DerekWilson - Wednesday, August 31, 2005 - link
I am not sure if I want to go with active amplification. I understand that stressing the opamps on the card towards the top end of their range could adversly affect their linearity. But my impression is that spending this much money on an audio card means a listener should not have to invest in an amp to get the best quality sound. We want talk about the audio as it will be heard by our readers.Do you have a different opinion on the subject?
And thanks for the suggestions on speakers and other headsets.
SDA - Wednesday, August 31, 2005 - link
>>I am not sure if I want to go with active amplification. I understand that stressing the opamps on the card towards the top end of their range could adversly affect their linearity. But my impression is that spending this much money on an audio card means a listener should not have to invest in an amp to get the best quality sound. We want talk about the audio as it will be heard by our readers.Do you have a different opinion on the subject? >>
The amplifiers on sound card line-outs are rarely equipped to drive headphones, especially not extremely power-hungry one. While I agree there is value in an ampless test, I also feel that an amplifier would be a good idea for pure line-out performance. A lot of us don't put any real strain on the line-outs, after all, and I'd like to see how evening the playing field a little helps various cards.
At any rate, spending this much money on (insert piece of equipment here) never entitles a listener to avoiding another link in the chain entirely. Not that headphone amps are a necessity, but hooking a $200 headphone to a line-out of a $400 sound card is a little silly and probably wouldn't yield sound as good as a lower-tier sound card and a cheap headphone amp (the things don't need to be pricey, just gutsy enough to power any normal dynamic headphone with ease).
Xentropy - Wednesday, August 31, 2005 - link
Sorry this is a bit off-topic, but you seem to know what you're talking about, and everywhere else I've asked I've gotten audiophile answers (e.g. buy this or that $2000 piece of equipment), so......What reasonably priced headphone amp(s) can you recommend for use between a soundcard and a set of HD570's?
SDA - Thursday, September 1, 2005 - link
The PPA and M^3 are reasonably priced, at least from a DIY perspective. At a lower price point, PIMETAs are fine.If I were you, though, I would upgrade that HD570 first-- driver upgrade (meaning speakers or headphones) is generally much more noticeable than amp or source upgrade. If you like a bass-n-treble signature, try the HD590; if you like something bassy and trebley but with midrange in the bargain, try a Grado or Alessandro. A very simple amp / 'CMoy' (buy on Head-Fi or somewhere, they're overpriced on eBay) with a decent op-amp (OPA2134PA is fine) covers a surprisingly large amount of the gap between no amp and top-end amp-- the biggest thing is taking undue stress off of the sound card's line out.
Or, you know, buy a $3000 amplifier, and line it with sound-improving rainbow foil (hur hur hur).
mindless1 - Friday, September 2, 2005 - link
Personally I found an unbuffered design like a CMOY to be a more similar to a soundcard's line-out than to a Pimeta, PPA or M3... they're all fairly harsh with terrible channel separation.SDA - Friday, September 2, 2005 - link
What op-amp? An unbuffered design is bound to be heavily opamp-dependent.. I've heard some that I'd prefer a Sony D-33's headphone out to, and I've heard others that are 80% of a META42. A great op-amp might be terrible in an unbuffered design for current output reasons.mindless1 - Friday, September 2, 2005 - link
Just about any mid-grade or better? I find some of my favorites, like AD8610, AD843, and OPA637, all sound far better unbuffered than jellybeans like TL072 or old standards like JRC4556/8, BUT *almost* anything buffered beats them. Higher current chps like LM6171 give more current but still lack quality sound. I "almost" find completely dreadful, entirely unmusical general purpose opamps sound as good buffered as the average "good" opamps in an unbuffered configuration... and it doesn't even take much of a buffer to make that difference.This is of course keeping in mind the current limitations, they don't even sound very good at low output. IMO, a CMOY type design is only useful for higher Z cans that need a bit of a volume boost. Then again, vast difference in price too, some people have enough spare parts to crank out a CMOY on protoboard plus $10. CMOY is like a gateway drug, it only teased me onto harder habits.
SDA - Friday, September 2, 2005 - link
Wow... well, I guess our ears just disagree there, especially since the AD8610 is my favorite for unbuffered. I still prefer buffered, of course, I've just always felt that an unbuffered AD8610/20 or similar CMoy-type amp covers a good chunk of the gap. Well, each to their own, I suppose, and AT editors should be looking for something higher-end anyway.mindless1 - Thursday, September 1, 2005 - link
Well, LOL."Audiophile" <> reasonably priced... never has and never will.
However, a ballpark $200 headamp might be a "PPA v2" custom-built with AD843 opamps rolled in. Thee are a few lists of trade builders for PPA2 or other customizable amps that you can DIY, actually tailor to your cans, or to your tastes, there is a vast gulf between gamer pseudo-audiophiles that buy Creative Labs cards with digital tricks and those who simply want cleanest analog possible and bit-perfect digi out. Wheverver you fit into the grand scheme, may dictate the optimal amp for you.
Then you'll want another amp, and more cans, and another sound card, and a DAC, and... Sorry about your wallet. ;-)