What's New in PRAXIS
Version 2.51: fix to possible cause of false test pass results in AudioPass. (No effect on other Praxis use)
Fixed bug in amplifier gain measurement function in the drive calculator that used wrong probe values
Minor changes to the pass/fail limit file generation and limit testing
Added option to save data to WAV files with peak levels below fullscale.
2.49a: fixed problem where Schroeder curve generation would fail with some impulse responses
2.49: small changes to the popup control forms; enabled the "Esc" key when focus is on a plot form (so acquisition can be stopped). Added ability to convert Frequency Response plots made using Chirp from dBS to dBSPL units on the plot.
2.48 includes new menu options (Main Form, Config, Misc) to disable display of offset values and delay compensation value on plots (when they are not desired when printing). Also some labeling errors ("Res" rather than the correct "Re" in the Thiele/Small reports).
In version 2.48, if you export data from a polar plot (using File, Save As, Text Export Data Files), values for all angles and frequencies will be included in the text file (loadable to spreadsheet programs).
2.48 also has a modified calibration procedure when calibration is done with a ZBox-based system (like AudioPass) or using other non-standard probes.
Version 2.47a fixes the Automatic Frequency Response script and the Automatic Postprocessing script (which were getting installed incorrectly). Thanks to Joachim Gerhardt for reporting this error.
Changes to help in locating and controlling mixers when running within Vista.
Several changes for the Thiele/Small extraction script (for AudPod) to improve form handling.
An Automatic Postprocessing script has been added to the package of built-in Praxis scripts. This is useful for things like smoothing response curves during measurements, etc.
For writers of scripts, the Logxxxx debug window has been changed so that it always appears on top of other forms. This done so that it doesn't get lost when working with Scripts that put a lot of forms or Plots on the screen.
Added option in Main Form Menu ("Config>Preferences>Query for Save at shutdown") so that PRAXIS will not ask to save configurations when shutting down. This setting is saved with configuration files. Set it as desired and then use "Config>Save As Startup Configs".
Changed folder assignments for Vista compatibility. When running in Vista (or later) operating systems, all data files and scripts will default to the "C:\Users\Public\Praxis" folder. In older operating systems, the default will still be "C:\Program Files\Praxis".
Changed to HTML ("chm") help system for Vista compatibility.
Revised Free/Demo mode scripts for Probe Calibration and Ground Resistance calibration, to address some timing issues and remove possible confusion about their operation.
Modified microphone correction file loading process so that data is automatically saved - the user can now simply load such a file into PRAXIS directly from a distributable disk (using the Config>Hardware Specific>Mic menu) and PRAXIS will make a copy on the default data directory.
Added "Convert Sample Rate" postprocess type. This makes it easy to convert the sample rates of time domain data to integer-valued sample rates.
Modified to avoid noise in first acquisitions when using MLS and MLSpink (synch types only)
Modified "Divide after FFT" procedure to eliminate possible "divide-by-zero" errors.
Impedance Troubleshooting Script added to assist in finding and fixing sources of problems when measuring impedance (AudPod mode only). Find it using the Scripts menu of the Main Form.
Fixed recent bug that caused input selection to not save properly in config files
Mic input selection no longer changes when inspecting or loading a mic correction file.
Added "Central Spectrum" postprocess (based on the AES paper on this subject by James Kates).
Added "Drive Calculator" to the Levels Form. This can be used to configure a measurement system for a desired Voltage, Power, or SPL level, when using approximately sinusoidal stimuli. This is particularly useful for distortion measurements. See Help for details. in v2.38, the relative test level for measuring PA gain is adjustable.
Now using faster memory manager (credits to Pierre Le Riche for FastMM, on Soundforge, for this terrific manager).
Bug fixed in Measurement Guides that sometimes prevented it from opening or caused error messages on shutdown.
Combined Frequency Response and Harmonic Distortion measurement (using Chirp[Async] stimulus) modified to show "sine equivalent" levels. Be sure to use sufficiently long (3sec or more) chirps for this.
* Fixed problem where acquisition would fail if computer is left on more than 49 days.
* Fixed timing related problem with synch mode when using newest M-Audio Transit driver for XP. This fix may also help improve synch with some other cards.
Print full screen option added to Plot forms
Plot forms have new option to allow keeping color scheme of the Primary form and using it for all later opened data files.
Includes new "Easy SNR and THD" script.
* Workaround for bug in "Audigy2 ZS Notebook" soundcard which records one channel delayed by 1/96000th of a second.
* Modified "Start/Stop" button operation to prevent accidental restarting of acquition when it is auto-stopping.
* Improved recovery from Hibernate and Standby (however, it is still recommended that you DISABLE those power modes when running PRAXIS!).
* Fixed printing bug with "Color Fill" when used without bitmap backgrounds.
* Fixed occaisional problem causing phase errors in impedance measurements.
* Bug causing Windows Mixer restore problems in some XP machines has been repaired.
Default directory for data file saving and loading can now be specified. See "Config" menu of Main Form.
New Input sources: "Virtual Out1" and "Virtual Out2", for use as a reference when Digital Output or Digital Input is used. (These are not yet documented, however).
Digital input and output can now be used for measurements (see Levels Form menu "Setup-D/A&A/D, Digital IO Matching" and related items).
What if you could listen to a loudspeaker's distortion by itself? PRAXIS now has a Distortion Isolation option for synchronous FFT and Time Domain acquisition, which provides a novel and audible way to separate the "linear" from the "nonlinear" in component or loudspeaker sound. Includes a new script, "Distortion Iso (Time Domain)", usable with your own WAV file sources, that automates this complex and very informative test. (How does PRAXIS do that?)
Download an example WAV file of a small two-way cone/dome loudspeaker playing blues rock at moderately high level. The left channel is the "linear" part with the effects of frequency and room response, and the right channel is the distortion part alone. Use any WAV player, or better yet, PRAXIS to load the WAV file into a Plot and the use the plot's "Listen" menu to listen to channels individually or together.
(The track is a portion of "Take Me With You", by the Jayhawks, from their CD "Hollywood Town Hall")
More Distortion Isolation WAV files, made on two different kinds of loudspeakers, using a portion of "Jacksons, Monk, and Rowe" by Elvis Constello and the Brodsky Quartet, highpass filtered to remove energy below 200Hz (to accomodate testing of a Monsoon dipole panel):
Cone DI of JMR.WAV : made with a cone type 2-way bookshelf loudspeaker.
Monsoon DI of JMR.WAV : made with a Monsoon MM1000 panel (which has weak output below 1kHz)
Updated manuals and Help files.
Multiple "Hold" curves now supported. Just press the [Ctrl] key when using the Hold menu.
New Polar Plotting script, including support for the Outline ET1 and ET2 turntables for very convenient, automated Polar response measurements.
Maximum Output Level Capability measurement (see our AES 117th Convention paper, #6267). The facility has been refined and documented, and there is now an updated script ("Maximum Loudspeaker System Output"). Use this to measure the short term output capability of loudspeakers and sound systems.
Revised Schroeder Curve and STI calculation (thanks to Pat Brown of SynAudCon for his assistance on this).
Plots can be grouped into "Plot Sets", which allow a number of plots to use the same screen area and be easily selected from a row of push buttons - greatly reduces screen clutter!
Time domain file sample rate conversion and data file appending.
"Listen" menu in the Plot Forms (under "File") for time domain data -- allows you to listen to a data plot's contents, using any soundcard in your system. Play in stereo, mono summed, or each channel alone.
New Acquisition types: "Impulse Resp Asynch" (1 and 2 channels). Intended for measuring room responses (without a cal or reference input channel). The 2 channel version can measure binaural IRs of rooms. Useful for Room Sound Convolution (part of the new "Time Domain Math" Postprocess option).
How can PRAXIS separate linear signals from nonlinear distorted signals?!!?!
No smoke or mirrors. Here's a brief explanation:
1) Praxis first measures the frequency response (and impulse response) of the loudspeaker in the room. Because this is done using a Chirp stimulus and at a moderate level, the impulse response that PRAXIS gets this way does not include distortions produced by the system -- it measures essentially with one frequency at a time and ignores harmonic multiples of that frequency or tones generated at other frequencies; characterizing only what happens at the one applied frequency.
2) Praxis next plays your "clean" program material (such as a music WAV file) through the system and records the acoustical output. That recording will, as always, contain frequency response effects of the system (including the room, in the case of speakers) plus any distortion generated by the system being measured.
3) Praxis then takes your "clean" original signal and convolves it with the clean impulse response, calculating the recording that the speaker/room should have produced IF if the system generated no nonlinear distortion -- that is, a signal that is still clean, but which does contain all the frequency response and room effects.
4) Then, for the last step, PRAXIS subtracts the clean "speaker response plus room sound" recording from the actual "played from the speaker in the room" recording. What is left is: the distortion created by the system, in the form of a time record which can be heard.
So, what does that get you?
You can evaluate whether the subjective sound of a speaker is mostly due to nonlinearities, or whether it is linear-response or room-effect related. If the isolated distortion is essentially inaudible, you can concentrate on response or directivity of your design. If the isolated distortion is noticeable or annoying, you can concentrate on linearizing the system.
You can hear what those nonlinear components sound like, by themselves, and evaluate how bothersome they really are (or aren't).
You can verify or debunk claims of novel distortion-reducing (or novel-distortion reducing!) methods with your own ears, getting the distortions isolated where they can be clearly investigated and their actual effects experienced.