FAQ: Frequently Asked Questions about Praxis
Hardware Compatibility and Soundcards
Operation and Troubleshooting
About the AudPod
How do I get started with installing and using Praxis (in either Full or Free Mode)? There's a lot of stuff there!
Download the document "Getting Started with PRAXIS" (pdf, 400KB), which will guide you through the installation process and toward the included documentation, scripts, and Measurement Guides.
Note that if you are only using PRAXIS in free mode for postprocessing of data files (and not for acquiring signals) such as when using it for Room Sound Convolution you do not need to do the "Getting Started With PRAXIS" process nor do any hardware installations -- just install the software and go!
What does Praxis mean?? According to Webster's Ninth New Collegiate Dictionary:
"Exercise or practice of an art, science, or
How much does
The Praxis software, usable in free/demo mode is...free! (download the software free). The Audpod interface/key is, however, needed for full access to all of Praxis' functions. For local pricing information, call your dealer - see: ordering information.
I just download the software but don't buy the Audpod, will Praxis still be of
any use to me?
When Praxis does not sense that the Audpod is connected, it runs in "Free (or demo) Mode". But Praxis' "Free Mode" does more than just show demos.
It provides a fully functional, and particularly fast and effective Thiele-Small (via impedance) measurement facility for woofers. You'll find that it outperforms programs and hardware costing hundreds of dollars. For free.
It provides a high resolution dual channel RTA spectrum analyzer (up to 1/48th octave) with a pink noise generator, averaging functions, and table readout of data.
It allows for handy display, printing and formatting of measured data from Praxis (and other measurement systems).
It is a handy display program for exchanging data curves (double click on compatible data files in Windows Explorer, and Praxis will open the data file document for display!)
These "Free Mode" capabilities are provided at no-cost for use by amateur or start-up speaker designers.
I be able to run praxis on more than one computer?
Yes, you can install it on as many computers as you like. However, all the features will not be available unless the AudPod is attached to the computer being used at the time. But since the AudPod connects via USB, this makes Praxis extremely portable between such computers..
Praxis do anything that Liberty Audiosuite couldn't?
Yes, quite a bit. Praxis will accomodate much larger data sizes, additional stimulus types (including high-performance "resynchronized chirp"), wider bandwidths, higher resolution, greater post-processing capabilities, shaped tonebursts, room acoustics calculations, "flex" windowing, and weighting files to name a few. It can work with laptop systems, too. For more details, download the Praxis manual.
Can Praxis do scripts like LAUD did?
No. It will do much more sophisticated scripts than LAUD did. You can program Praxis scripts using using graphical "RAD" (Rapid Application Development) techniques with DelphiScript (an Object Pascal derivative) or with VBScript (a Visual Basic derivative). Praxis scripts can control the Praxis measurement system, of course, but it can also access the Windows API or even start and control other programs outside of Praxis. The Praxis download includes the Liberty Script Designer, a Delphi-like programming environment for conveniently developing your own scripts.
How do I update my copy of Praxis to the most recent version?
Download the latest version from the Praxis Download Page. Then to install, merely run the PraxisInstall.exe file -- the installation program will replace any old versions of files from your previous installation (and will leave your configuration and data files intact).
There is normally no reason to uninstall the previous version. However, if you should wish to start with completely fresh settings, first uninstall Praxis (using the Windows Control Panel "Add/Remove Programs" function) and then delete the entire "C:\Program Files\Praxis" directory (where "C:\: is the drive on which you have Windows installed).
Hardware Compatibility and Soundcards
compatibility issues are known about using PRAXIS with various hardware?
See: Compatibility Issues
Praxis work with all soundcards?
Praxis is intended to work with all Windows compatible soundcards that meet some minimum standards:
True full duplex at 16 bits (24 bits also supported), stereo mode
sample rate at 48kHz (rates to 192kHz are supported). PLEASE NOTE THAT 192kHz sampling is supported only by Windows XP SP1 and above! (operating system limitation)
Must have stereo Line input and stereo line output connectors. NOTE THAT SOME LAPTOP COMPUTERS THAT LACK STEREO LINE INPUTS DO MAKE THESE AVAILABLE IF USED WITH THEIR DOCKING STATIONS. You can also use Praxis with external USB soundcards such as the M-Auido Transit, the EGOSYS U24 or the Maya 5.1USB.
Must NOT have hardwired record-->play or play-->record monitoring (such features, if included, must be able to be switched out via the system mixer applet).
Have good, reliable, and fully-debugged Windows 32 bit drivers.
Also see: compatibility issues
have a measurement microphone -- can I use it with PRAXIS?
Yes, provided that the microphone:
Has calibration data available -- in other words, you need to know what its response is and the value of its relative sensitivity (in mV/Pa). Phase response information is also helpful, but you can still use the microphone without it. You will need to generate a response calibration file for the microphone using a text editor (such as Windows notepad), and name it "yourmicname.dat". You can find an example file showing the format here.
Is self-powered. The AudPod can provide bias only for the Girardin microphones, others must provide their own bias from internal supplies or a supply/preamp.
Has a 1kHz sensitivity between about 2mV/Pa and 30mV/Pa. If the mic sensitivity is higher than this, you may be able to use a commercial attenuator to reduce it.
Can be adapted to the 3.5mm mini-phone connector of the AudPod. If you connect to the AudPod's mic input, you must adapt your mic's connections to one side of a phone plug (single ended).
Alternately, you can adapt your mic to BOTH sides (balanced connection) of a 3.5mm mini-phone plug and connect it via the AudPod's "Probe1" input. The tip connection is the [+], the ring connection is the [-]. This connection provides about 12dB less gain (and 12dB higher signal level handling). See Praxis HELP files under the topic "Microphones" --Alternate Microphone Connection.
How can I make an attenuator so I can use a high output voltage microphone with PRAXIS?
For high SPLs, the microphone sensitivity needs to be low. Even with 1mV/Pa, a 166dBSPL would be 4V output, too much for even most line inputs. This could be handled with an attenuator. The tradeoff is of course signal to noise. Ideally you would use different mics for different purposes, or at least different attenuators.
An attenuator for a microphone could be as simple as a series resistor. The AudPod's mic input has an impedance of 3.45K ohms. A series resistor R (used between the mic preamp's output and the AudPod's mic input circuit) will scale the output by factor F=3450/(R+3450). The AudPod mic input can deal with levels to about 700mV peak, so leave some margin and assume 500mV. If you need to measure to sinewave levels of S [dBSPL] with a mic that has sensivitiy of M [mV/Pa], then calculate:
Max microphone output voltage Vmax = 10^((S-94)/20) * M/1000 [V]
Look up your mic's output impedance Z = (usually 150 ohms)
Scale factor F = 0.5/Vmax
Use Resistor value R = 3450/F - 3450 -Z [ohms]. Make an adaptor that simply has this series resistor included.
The new effective sensitivity of the mic is then F*M, so edit the microphone's "dat" file so that the value in the first line (where it reads "mV/Pa") is changed to the new sensitivity. Save that files and load it using PRAXIS' "Config -> Hardware Specific ->Mic" menu.
Example: Say you have a mic that has 17.8mV/Pa sensitivity and that it is usable to 155dB SPL (and you will be using it to that level). Vmax is then 19.97 [Volts]. The needed scale factor is 0.025. The series resistor to use is 134.4k ohms (use the closest 1% value, 133k ohms). The actual scale factor is then 0.025284, so the new sensitivity of the mic, when the attenuator is used, is 0.450 [mV/Pa]. Edit the file accordingly, and make your attenuator adaptor as shown below:
For use with ACO microphones and supplies, Liberty Instruments
has attenuators like these available.
(note that the output of a microphone having 150 ohms output impedance will be reduced from its "open circuit value" by 0.37dB when loaded by the Audpod's microphone input without an attenuator resistor.
kind of computer do I need? Does computer speed matter with Praxis?
Liberty Audiosuite (DSP based) was known to be quite immune to limitations of computer speed. Praxis, however, relies on the horsepower of your main processor (which is also busy running the Windows OS), so faster is definitely better! The following are minimum and recommended characteristics of a computer for Praxis:
Clock: 500MHz recommended minimum; 800MHz or higher preferred; Athlon or PentiumII/III/IV processors are preferred. (development was done on a 366MHz Celeron machine).
Motherboards based on Intel, AMD, or Sis chipsets recommended. See: compatibility.
RAM: 64MEG minimum ; 128MEG or more recommended
Video: (video speed helps with praxis). AGP recommended. Graphic acceleration not an advantage (but not a problem).
MUST have a free working USB port (for the AudPod). (But USB port not needed for Demo mode operation).
Operating System: Windows 98SE, WindowsME, Windows2000, WindowsXP.
Free disk space: at least 25MEG.
soundcards, motherboards, and operating systems are safest (least likely to
cause surprises) with Praxis?
The safest motherboard choices for Praxis are those based on Intel chipsets and Celeron processors (PIII or P4 are good too, but more expensive). Intel manufactured motherboards are also good choices. Of course most other types (AMD, VIA, etc) will normally work fine, but are more likely to have "surprises". This is only because manufacturers of cards, USB devices, etc. will usually make SURE that they work as expected with the standard Intel stuff, but may check less thoroughly with the other brands).
We no longer suggest the "Soundblaster 128" soundcards, as some boards sold under this name use a different chipset ("Vibra") and would not calibrate in at least one system. But for a reasonable expenditure you can instead go all the way to 24bit/192kHz performance with the Waveterminal 192X., or for less money, the Waveterminal 192L.
We would NOT recommend the Soundblaster Audigy at this time, as it needs special attention to get it working with Praxis (it defaults to monitoring!), and has no apparent special performance with Praxis that would justify its higher price. (Despite its marketing literature, it is not in any way a 24/96 card!). We haven't tested Audigy 2 yet, but would recommend that if you are planning to buy a premium card, you'd be better off getting the real thing and going with the ESI Waveterminal 192X, at comparable cost.
If you need a USB-based soundcard, the most trouble-free ones we've seen are the M-Audio Transit (highly recommended), the ESI U2A or U24, or the AudioTrak Maya 5.1 USB.
For best overall performance (24bit, 192kHz, fast operation), try the Lynx L22. The LynxL22 is rather expensive however, and its setup is more involved (but there are detailed instructions for it on our web pages). A less expensive, choice approaching the same performance (and offering very simple setup) is the ESI Waveterminal 192X. PLEASE NOTE THAT 192kHz sampling is supported only by Windows XP SP1 and above! (operating system limitation)
more detailed info: also please see the Soundcard
The best operating system to use for Praxis is Windows 2000. XP is a good second choice (but is still newer and so has more bugs in general). WindowsME or 98SE can work, but have limitations in the number of Praxis Plots (and other Windows forms shown simultaneously ) that can be handled simultaneously. ME is rather a pain in general (plan on crashing at least once a day with it, no matter what programs you run on it!).
any benefit(s) be gained from the utilization of high-end audio cards? Any
With 24bit cards (such as Waveterminal 192X, CardDeluxe, M-Audio 410, 1010 or Audiophile 2496, or Lynx L22) you could measure to lower distortion residual level for electronics. But for loudspeaker work there is no real advantage to 24bit operation (you'd never find an environment or microphone with enough dynamic range or low enough distortion to make use of the additional bit resolution).
If you want to measure above the normal audio band, a 96kHz sampling card will allow you to get to about 40kHz. A 192kHz card (such as the Lynx L22 or Waveterminal 192X) will allow measurement to 80kHz, though the higher frequencies will be subject to increased crosstalk between channels from our AudPod (which was mainly designed for operation below 50kHz). PLEASE NOTE THAT 192kHz sampling is supported only by Windows XP SP1 and above! (operating system limitation)
Praxis work with digital inputs/outputs on soundcards?
Yes, it can work. However, calibration (to true voltage or sound pressure levels) will not be possible except when these ports are used with additional converters that provide or accept analog signals. ("Bits" are not Volts, so they can't be calibrated!).
thinking of getting a new soundcard -- can you recommend any for use with
For a reasonable expenditure you can go all the way to 24bit/192kHz performance with the Waveterminal 192X. or to 24/96 operation with the Waveterminal 192L. Also see: recommended hardware. In general, the following are some pointers about good cards for Praxis use:
SIMPLE is GOOD! Extraneous features such as "Environmental sound", "CMSS",. 3D processors, Karaoke, MP3 converters, monitoring functions, sample converters, zillions of channels.... those are all complicating factors that often require workarounds (or could even make a given card unusable if the feature can't be completely avoided). Essentially, you need clean, reliable, 2-channel record and play functionality. Other nonsense may or may not hurt -- but it will definitely NEVER be an advantage!
Make certain that the card has a stereo line input (that it can record from) and a stereo line (or clean headphone) output. Praxis will not work with "mono only" inputs! (But a large array of input and output jacks is not helpful: simple is best). NOTE THAT MOST LAPTOPS PROVIDE STEREO LINE INPUTS ONLY WHEN USED WITH THEIR DOCKING STATIONS. But some don't provide stereo line inputs at all. Most built-in sound hardware in laptop computers is of medium to poor quality, and often cannot be used practically with PRAXIS -- for portable use, the best option is to use a USB soundcard like the U24 or Maya 5.1 USB or the M-Audio Transit.
Avoid hardware gain controls (external physical knobs). These can interfere with Praxis's calibration stability. If used, be careful to always use Praxis with these knobs set to exactly the same positions with each use.
Stay with cards that are simply sound cards (rather than "combo" cards that also are modems/videoports/pro-MIDI synthesizers, etc.).
heard there are restrictions with certain cards. What's the story on this?
Many soundcards internally use only one hardware sample rate (usually 48kHz), and provide support for other sample rates via a technique called "rate conversion". Some implementations of rate conversion do not maintain a steady, repeatable mapping between the "native" rate and the desired rate, and thus cannot be used for synchronous measurements (measurements in which data from one burst is used to timestamp or average with a data set from a different time -- an example is synchronous MLS). For example, a "Soundblaster Live" will only work with Praxis's synchronous measurements at the rates of 48kHz and 24kHz. For non-synchronous uses (such as RTA measurements), however, there are no such restrictions. As a practical matter, the restriction causes little or no problem, it only requires that you use the synchronous rates for synchronous measurements -- so, just use 48kHz (which is what you usually want anyway!) and there is no problem.
Some lower grade cards (or on-board audio chips) have shown occasional problems with varying latency, which can sometimes cause errors with averaging processes.
The performance of sound hardware built into some motherboards or laptops can be limited by noise floor or high distortion.
Praxis work with laptop computers?
--provided that the sound hardware meets the requirements specified above. But most built-in sound hardware in laptop computers is of medium to poor quality -- for portable use, the best option is probably to use a quality USB soundcard like the Transit, ESI U24 or Maya 5.1 USB.
Most laptop computers are equipped with some means to slow down the processor during periods of low usage. THIS POWER SAVING FEATURE SHOULD BE DISABLED WHEN USING PRAXIS, as its initiation can interfere with audio data streams and cause problems with measured distortion, synchronization, and spectrum noise floors. You can find the controls to disable this in your Windows "Control Panel".
Operation and Troubleshooting
I downloaded the Praxis file(s), but it won't install.
Sometimes file corruption can occur during download, or your browser software may incorrectly report that all of a file has been downloaded when it has aborted because of an interruption. If you are having troubles downloading, try to download the individual 1.4MB files rather than the big all-in-one file, and check that all files but the last are approximately 1400kB in size. If any (other than the last one) are smaller, download that one again before trying to install.
I get relatively high distortion when using the Maya EX (or Maya 5.1USB)
The Maya EX is USB powered, so it has some trouble achieving high output levels with low (<0.1%) distortion at the line outputs. One solution is to use PRAXIS with the Output Levels (in the "Levels" form) at -5dB.
A better approach is to connect the Maya's "headphone" output to the AudPod's "From Sound Line Out" jack (instead of feeding this from the Maya's line outputs). The headphone output has better output drive and lower distortion at high levels.
I see low level spurious tones in FFTs when I use my USB-connected soundcard
This can be caused by ground loops and inductive pickup when using excessively long cables to connect between the USB soundcard and the AudPod. The 12-foot cables supplied with the AudPod are not good choices, and are not necessary for this connection to a USB card! The spurs can also be caused by internal noise in the USB card (from its microcontroller), but in better cards such as the Transit, the spurs will all but vanish when cables of 12inches or less are used.
Measurements made with PRAXIS are changing when I move the cables going to the soundcard, the microphone or the AudPod.
One possibility is that an internal connection in one of the cables is intermittent. This may be the case if bending the cable (near where it meets the connector molding, but without moving the connector to its jack) causes the measured signal to abruptly change.
Another possibility is that there is an oxidized or dirty contact inside or going to the AudPod. You may want to get some CAIG "DeoxIT" contact cleaner, or a silicone-based tuner cleaner from an electronics dealer such as Radio Shack, spray some on a cloth, and wipe it onto all connector contacts -- then work these connectors back and forth a little into the AudPod's audio connectors to clean both the plugs and the Audpod's jacks. Doing this can do wonders.
During soundcard calibration, in the Playback Mixer adjustment, the blue bar-graph shows at full scale no matter where I set the mixer controls!
The output slider adjustment process during soundcard calibration can be confusing.
The brief answer is:
Make sure you really did have the Windows Playback Mixer set for full scale (or near-full scale) in the step PREVIOUS to the step where you are asked to adjust the mixer for the bar-graph!.
The long answer, with explanation is:
It is very important to note that the blue bar graph during playback mixer adjustment doesn't show absolute level -- it shows relative level. That is, it is showing an indication of the current level, relative to the signal that was detected and determined in the previous step of the calibration. What PRAXIS is trying to do here is to get you to set the output gain slider to a setting where a full-scale output signal is coming out of clipping. The step just before, where previous instructions directed you to have the slider at or near full maximum, is assumed to have been clipping the output during a test that PRAXIS runs when you proceed.. When PRAXIS runs a sinewave in the "bar graph" step, and sees the peak level at something less than the previously measured level (the Red dot goes out), then it knows that you are no longer clipping. BUT, if the level controls were not really set for clipping (or at least for a large signal) in the previous step -- a common error seems to be that people try to start with the level sliders at minimum or with them muted -- then PRAXIS can NEVER detect a signal less than that -- except randomly from noise. This is usually what is happening, should you find that changing the slider shows the bar graph at full scale no matter where you adjust the mixers. If you didn't get a near-clipping reference, but by chance get past the "bar-graph" step, the calibration will usually fail at a later step, when it tries to distinguish one playback channel from the other or to determine output polarity-- two channels with low gain show insufficient difference in level when one is turned off. So the moral of that story is: make sure you start the calibration with the playback level controls cranked. (There is one exception -- some few very high output level cards, such as the CardDeluxe if set for "pro" level, can overdrive the AudPod if full gain is used; for these, you may need to start with the output level at about 75% of full scale if calibration problems should appear).
I can't get the Maya 5.1USB soundcard (or other compatible USB soundcard) to calibrate in PRAXIS
Before doing the calibration (Levels Form,
"Setup, Do Calibrate" menu) procedure:
Make sure that PRAXIS is set for 16 bit operation (in the Levels Form, "Setup, D/A&A/D" menu) and that the "WAVE_EXT" menu option (of the Main Form, "Config, Hardware" Specific menu) is checked. And that the proper soundcard is selected in the Levels form!
I can't get the soundcard calibration process to succeed with my soundcard.
This can be tricky with some soundcards and operating systems. There are a wide range of characteristics, performance parameters, and functions for all the different makes and models of soundcards, and over the various Windows operating systems and drivers. In some cases the direct procedure of the Praxis Hardware Calibration guide (for AudPod use) will not be able to sort it all out automatically and will need more effort. You can find some specifics of calibration results, and the settings needed for certain mixers, using a number of soundcards in Windows 2K, ME and XP, including some particularly troublesome cases at our new Sound Card Calibration Pages.
does PRAXIS deal with the soundcard Windows mixers?
See: PRAXIS and Windows Sound Mixers.
I'm having trouble getting Praxis to operate with my soundcard. I get an error message "WAV failed at start". What should I do?
Praxis can be configured to use one of two types of soundcard APIs. Some soundcard drivers (usually not "WDM" types) are not able to use the so-called "WAVEFORMATEXTENSIBLE" structure. For these, uncheck the menu option "WAVE_EXT", which can be found on the Main Form, under "Config, Hardware Specific". To make this setting your default, close down Praxis afterward (and allow it to save all configurations).
This message will appear if the soundcard device cannot support the bit resolution or sample rate that is requested.
This can also happen if your soundcard's driver freezes or crashes for some reason. Usually the only way to fix that is to reboot the system. (It may be a good idea to see if the soundcard manufacturer has issued a fixed driver, too).
I can't operate my 24bit capable soundcard with 24bit capabilities -- Praxis does not allow me to select 24bit mode.
With soundcards using "WDM" type drivers, 24bit operation can only be obtained by using the so-called "WAVEFORMATEXTENSIBLE" structure. For these, check the menu option "WAVE_EXT", which can be found on the Main Form, under "Config, Hardware Specific". To make this setting your default, close down Praxis afterward (and allow it to save all configurations).
The noise floor in my spectrum plots swells or rises periodically, particularly when using larger FFT sizes.
This usually indicates that record or playback samples are being corrupted or dropped for some reason. When Windows is unable to keep up with audio streams (because it is too busy, or gets interrupted by high priority operations) it will sometimes just toss out or ignore sections of the audio stream. Possible causes are:
Initiation of power-saving modes (particularly in laptops) these features can usually be disabled in the Control Panel.
Inadequate processor speed for the hardware used (some soundcards use more processor assistance than others), and for the Praxis operations being attempted.
Try to connect USB soundcards directly to the computer's USB port, rather than through hub, if you have the choice. The AudPod and devices like a computer keyboard or mouse can be connected via a hub without any problems, though.
The computer may be getting distracted by other operations, network activity, incoming mail, etc. Shut down unused programs and unnecessary connections.
When I measure the frequency response sensitivity of my loudspeaker, the values seem to be about 9dB lower than the results from measurements with LAUD or with other systems. Am I doing anything wrong?
This happens because Praxis reports acoustic to electronic sensitivity in terms of SPL normalized to 1Vrms drive (this is called "dBS" on Praxis plots). This is different from some measurement systems which report sensitivity in terms of SPL normalized to 2.83V (2.83V represents 1Watt with an 8 ohm resistive load).
Because what is actually being measured is voltage during such a test, and because loudspeakers do not always have an 8ohm impedance (and are virtually never resistive loads), the normalization to 1Vrms was deemed to be more correct and makes no assumptions about the nature of the load.
It is easy to convert from
"dBS" to "dBSPL at 2.83Vrms applied". Simply raise the
curve by the factor
20*log(2.83) = 9.03dB. You can accomplish this by entering this value into the "Offset" control that can be found on the "Weighting" tab of the Plot Forms.
A better question is "why would you want it to?". The measurement is not MADE at 1Vrms (usually), but the resulting sensitivity value is referenced to the 1Vrms drive level. Think of it as being like the speed of a car - you can drive at 60mi/hr without driving for an hour or for 60 miles. You can go 60 miles/hour for just 10 seconds and the speedometer will still read correctly. But if you did drive at 60mi/hr for exactly one hour, you'd go....60 miles. Don't confuse ratiometric measurements with absolute measurements.
The volume level you measure with doesn't matter (provided you don't overdrive anything by being too loud or get buried in noise by being too low), as long as PRAXIS can determine the ratio of sound pressure to drive voltage. The best check for overdrive is to reduce the volume control on your amp and see if you get the same ratiometric answer as at the higher level. If so, you can trust it.
If the applied level DOES matter, then you are in the realm of distortion measurements, not frequency response measurements!
Why can't I select the frequency range when I measure frequency response using Chirp stimuli?
order to let you window out reflections, PRAXIS
any Chirp measurement which needs to pass through
I think my Calibration files or my Praxis Configuration files may have become corrupted or damaged. How can I start again with new Configuration or Calibrations?
If you find that PRAXIS no longer seems to start up or work as before (when it had been working correctly), but recalibration does not seem to help, it is possible that the problem could be an error or data corruption in either a calibration file or the PRAXIS configuration files.
One way to avoid propagating damaged configuration or calibration values is to uninstall PRAXIS, delete the entire "C:\Program Files\Praxis" folder, and then re-install PRAXIS. But if you do that, you could also lose data files you may have generated. To keep the installation and data files, but start with fresh Calibration Files and/or Configuration files, close PRAXIS, then do the following:
For Configuration Files: Browse (in Windows Explorer or "My Computer") to your "C:\Program Files\Praxis" directory and find the files named "Praxis.ini" and "Praxis.hdi". Rename these to something else (such as PraxisOld.ini and PraxisOld.hdi". Also, rename or delete the file "PraxisSaveData.pbu". These steps will force PRAXIS to start with default settings and to make a brand new configuration file. Your data files will still be available, but the settings for scaling, formatting, etc. will go to the "new installation" defaults. You will again need to select the sound card to use, select the microphone calibration files, and make any other settings that are needed with a fresh PRAXIS installation.
For Calibration Files: Browse (in Windows Explorer or "My Computer") to your "C:\Program Files\Praxis\AudPodMixer" subdirectory. Rename that subdirectory to something else (such as "AudPodMixerOLD"). This will force PRAXIS to create a new subdirectory with all new calibration files and device-mixer matching records. Then start PRAXIS and try to recalibrate. You will need to first check and "OK" the device-mixer matching settings, and select your desired soundcard, rate, resolution, etc.
About the AudPod
So, what does the AudPod do?
Quality microphone/accelerometer preamp
Consistent, automated, precision input gain control
input protection from large signal voltages
differential (instrumentation style) probe input interfacing
calibration reference oscillator for calibration around a wide range of soundcard hardware
input selection for two channels (2x mics, 2x probes, 2x Aux, Stimulus channels, ref oscillator)
hardware key for more sophisticated software functions
It is NOT a USB-based soundcard (does NOT do A/D and D/A) -- it is a digital controlled analog interface.
The AudPod is powered by the USB port (no batteries or wallwarts to fuss with), is direct coupled (frequency response down to DC), and contains an internal microcontroller and symmetrical power supplies. It is housed in an attractive, rugged, and handy 3"x4"x1.3" extruded aluminum enclosure.
What are the AudPod electrical interfaces?
Microphone Input (2 channels on one 3.5mm stereo jack):
Input loading impedance 3.45k ohms.
Bias = 4.0V via 3.57K ohms
Usable with Girardin microphones, same correction data as used with LAUD
Can be used with externally powered microphones having capacitor coupled outputs. Recommended sensitivity between 3mV/Pa to 20mV/Pa (depending on required signal handling and sensitivity
First stage gain is 12.4dB, AC coupled.. First stage output overload is 6V peak to peak.
Second stage available gain (after adjustable attenuator) is 23.5db, DC coupled, output impedance is 100 ohms.
Protected to 40V peak.
Probe Inputs (2 channels, each on a separate 3.5mm stereo jack):
Each input channel has two differential inputs, one [+], one [-].
Probes include (2) series 47.5k ohm resistors in each input phase.
Each input phase can handle to 40V peak AC+DC (additional external dividers recommended for higher voltages)
First stage gain (with 47.5k probes) is -22.6dB, DC coupled. First stage output overload is 7V peak to peak.
Second stage available gain (after adjustable attenuator) is 23.5db, DC coupled, output impedance is 100 ohms.
Aux Inputs (2 channels on one 3.5mm stereo jack):
Input impedance approximately 40k ohms
Protected to 40V peak.
Single stage, available gain is 23.5dB
Stimulus Output Characteristics (2 channels on one 3.5mm stereo jack):
Determined entirely by the soundcard being used. Output is passed through the AudPod passively without processing, for minimum distortion.
Output can be selected to an input source, for loop testing or synchronization, additional loading under 30k ohms.
Interface to Sound Line Out (2 channels on one 3.5mm stereo jack):
Pass through to Stimulus Output connector, with selection to input
Drive level should be kept below 3V peak (6V peak-peak) to minimize crosstalk into inputs.
Input impedance, 40k ohms in parallel with load on Stimulus Output jack
Interface to Sound Line In (2 channels on one 3.5mm stereo jack):
Drives sound card line input
Maximum possible output level 3.5V (peak)
Driving impedance, 100 ohms
low speed USB, used for control
powers AudPod from hosts USB port, usable from unpowered USB hubs (maximum current drain is 100mA).