Making 96kHz Sample Rate Measurements with
PRAXIS on a Laptop
with the Audigy 2 ZS
last update 9/25/2005
Blasted again: There is a hardware bug in the Audigy2 ZS cards (and presumably the other Audigy2 cards) causing phase shift problems with this soundcard! In recording, one channel is offset in time by one 96kHz sample, which gives erroneous phase measurement results for frequency response and impedance measurements. A Patch is included in PRAXIS v2.30 to workaround this until such time as Creative Labs fixes this. The article below details other steps needed to work with the Audigy2 ZS PCMCIA soundcard.
This is something we get asked about ALL THE TIME. More and more people are wanting to be able to make measurements to 40kHz, so they need to sample at 96kHz or more. PRAXIS can handle this. But most inexpensive, portable, laptop compatible sound cards won't.
USB soundcards for use with laptop computers are a mixed bag -- the M-Audio Transit (a favorite) is 96kHz capable, but not when simultaneously recording and playing (called "full duplex"). The Audigy 2 ZX (a USB2 card) will do it, but it is rather a pain to set up and operate and also needs access to a wall outlet, which is a significant nuisance. There are several Firewire cards available (such as the M-Audio Firewire Audiophile, and the Terratec Phase 24) which we have used or had good reports about, but these are expensive, and most notebook computers don't have Firewire ports yet. The Digigram PCMCIA soundcards are just too expensive for many of our users. The Echo Indigo IO PCMCIA card seems to exhibit some sort of bug or conflict with PRAXIS, at least on some laptops, that causes it to cease acquiring input a short while after being started each time. Considerable effort from us and the helpful engineers at Echo has failed to find the cause for this strange problem.
Now there is the Audigy 2 ZS Notebook, a PCMCIA card made by Creative Labs that claims to do 24bit/96kHz, and costs only about $125 retail. It's system requirements are a bit intimidating: 1.5GHz minimum clock speed! But we don't want or plan to use all the fluff features (7 channels, "CMSS", "EAX" etc.), we just want two channels of reliable, unprocessed input and output and no funny business.
I haven't been very fond of Creative Labs soundcards here, in general, for a couple of reasons. First is the obnoxiously large software load the driver and installation disk wants to inflict on your computer -- irritating popup splash screens, overly complicated configuration panels, and lots of tossed-in applications. Some of the applications may be interesting to those using the soundcards for games (at least for a few minutes before the novelty wears off), but they are seldom worth the disk space or the extra Windows startup time. The installation also puts icons on your screen, and whenever driver updates are performed, all your settings get changed (and any icons you cleaned out get put back in).
My second gripe is with the sample rate conversion scheme that Creative Labs cards use when recording. The cards internally sample at 48kHz (or 96kHz in the newer Audigy 2 cards). For lower sample rates they use a conversion scheme that appears to skip enough scattered samples to get the rate down to the desired amount. This is not very clean, and makes it impossible to time synchronize to the extent needed for measurements (such as with MLS) at these simulated sample rates. So you mostly have to use the card at its actual pure internal sample rate or at an even sub-multiple of that rate, if you want to use PRAXIS' synchronous modes. That's really not much of a restriction, though, as 48kHz or 96kHz are pretty much the only rates most PRAXIS users use, at least, anyway. But it is another complication and something to have to remember (and it also seems to be a chintzy way of providing multiple sample rates, particularly for something priced like a premium soundcard).
Another concern with Creative Labs cards is that they have been known to market distinctly different types of hardware under the same model name. This is unlikely to the be case with more limited-market items like the Audigy 2 ZS Notebook, though.
We have received some good reports on the Audigy 2 ZS Notebook card with PRAXIS, so we got one in for testing. The conclusion, in short is good: It can work, doing 96kHz and 48kHz sampling reliably, even on a 650MHz Celeron Notebook computer (a Compaq Armada M300). But some of the expected Creative soundcard hassles are still there, so below are some guidelines for getting it going while avoiding the negative aspects..
The performance is quite good at 96kHz and at 48kHz. PRAXIS' synchronous modes cannot be used at the 22kHz or 44kHz modes because of the quirky sample rate conversion method. The device also operates at 88kHz, but the floor of spectrum plots becomes messy then, with lots of spurious tones, so just use 96kHz for high rate measurements. The card also supports 24 bit operation, but, like with most soundcards, there seems to be no advantage in using this with PRAXIS -- the noise floor and distortion residual (about 0.003% at midband) is exactly the same as when using 16bit. Using 16bit is easier on the computer and allows for smaller file sizes and is much less likely to cause speed issues or lost samples.
Disclaimer: Your mileage may vary!
The Creative Labs documentation for this soundcard warns that there may be compatibility issues when it is used with some PCMCIA port hardware and with some laptop computers, which may keep the device from operating in its "High Performance Mode" (which is needed to use it at 96kHz sample rates). So you may want to check for the return policy of your Creative Labs dealer before taking the plunge... Though, the price of this device really isn't bad even if you have to use it at 48kHz, and it makes a really compact, convenient measurement package.
1) Follow the installation instructions for the card, but install ONLY "Audigy 2", and unselect "Creative MediaSource" from the application sets to install..
2) During that process, you will be given a selection of other things to
install. Select only the following:
"Drivers", "Creative Audio Console", and "Sound Blaster Performance Utilities". Skip the rest, to save time and disk space.
3) Every time you install another component, the disk will helpfully install a "Free AOL!" icon on your desktop, and a matching entry on your start menu, without asking your permission -- just in case you've been living in a cave for the last ten years and have never been in a computer store, grocery store, carry-out, or any of the other places that offer free AOL disks! ...so you'll have to delete the icon and start menu icon after each installation if you want to feel like you still own your computer.
4) Before actually using the card, get on the internet and go to Creative Lab's Website, locate their support and drivers page and update to the newest driver for the Audigy 2 ZS Notebook. Do this now , before proceding, because the update will reset many of the settings that are to be described next! If you update drivers later, you will have to repeat items 5 and higher, below. As of this writing, the file is "2.03.00 SBA2-NBDRV-W2-LB", dated 9 March, 2005.
It is also possible that Windows' Automatic Update could update the drivers sometime later without you noticing -- so if PRAXIS suddenly starts measuring strangely after a future Windows Update, it would be a good idea to check the following settings again! Also, PRAXIS soundcard calibration should be repeated after any related driver update.
5) Start the "Sound Blaster Performance Utilities" application (from the Windows "Start" ->"Programs" ->"Creative" ->"Soundblaster Audigy 2" menu). A little green icon should appear at the right-bottom of your screen (the Windows "tray"). Click that icon, and a small menu should appear. In that menu, select "High Performance Mode" if it is not already selected.
There is also a "Performance Diagnose" option that may be able to tell you whether the card can handle the High Performance Mode.
6) Using the Windows "Start" ->"Programs" ->"Creative" ->"Soundblaster Audigy 2" menu again, open the application "Creative Audio Console". Select the tab labeled "EAX", then click on the round button marked "Custom", then double click on the words "(No Effects)" which are under "Active Preset". The form will vanish.
7) AGAIN, using the Windows "Start" ->"Programs" ->"Creative" ->"Soundblaster Audigy 2" menu, reopen the application "Creative Audio Console". This time, select the tab labeled "CMSS 3D" and set "CMSS Modes" to OFF. This is very important. Using any Creative installation or driver update will reset CMSS to ON without asking you, which is very bad for measurements. If you ever find that measurements are not working correctly, check this CMSS setting and make sure it is OFF.
This seems to be true of all newer Creative soundcards -- they always want to turn CMSS back on at every opportunity (such as whenever you run any installation from the driver disk).
8) Then, still in the "Creative Audio Console", use the "Speakers" tab and make sure that the checkbox "Synchronize with Windows Control Panel" and then select "2/2.1 Speakers" from the drop-down control. Then click the "Close" button at the bottom of the form. Evidently, different speaker settings causes equalization or other effects to be applied.
9) Open up the "Creative Audio Console" yet again, and click its "SPDIF I/O" tab. Set "Digital Output (PCM) Sampling Rate Settings" to 96kHz.
10). Still in the "Creative Audio Console", click the "Bit Accurate" tab and put a checkmark in the "Enable Bit Accurate Playback" checkbox.
(These last two steps are required for more recent revisions of the Audigy2 ZS drivers).
Be sure that your PRAXIS version is v2.30 or later. When using PRAXIS, make sure all the power save options of the laptop are disabled (these controls are in the Windows Control Panel). You should also disable all screensavers (right-click on the empty desktop, and select "properties").
Now you can connect your AudPod to the laptop's USB port, and run short cables (the shorter the better) between the soundcard and the AudPod. Then, start PRAXIS, do any "Mixer matching" it requests, select the new soundcard and do the PRAXIS soundcard calibration process. Here are the mixer settings I ended up with (using Windows 2000). The "tone" controls of the Play Control (not shown) were not adjusted, and should be left set for a flat response.