Audio.TST February 2008 P1 calibration & Best Practices for APx coding

Created 02 Feb 2008

Notes from the Test Bench

By Bruce Hofer, Chairman & Co-Founder, Audio Precision

2008 is proceeding quickly. NAB is already on the horizon, and our product development team is hard at work on the next release cycle of APx. We also have a team of engineers in Asia listening to customers about new test techniques and discussing possible new features for APx.

Here at the Factory, I'm pleased to announce that our Calibration lab has finished the work required to launch calibration services for the ATS-1 and later versions of the P1. Our Tech Support group is also

continuing to release new resources for APx API developers. It is always rewarding to me to see the completion of a significant technical effort.

Finally, I want to congratulate our fine network of distributors and representatives who work so hard to provide the highest level of service to all AP customers. I consider these people to be critically important extensions of our AP body, and wish to recognize their many helpful contributions besides the generation of sales. However, speaking of sales, I would be remiss in not also recognizing our fine team for setting yet another all-time record high in 2007.

Bruce

Output: Tech tips and new applications from AP

Accredited Calibration for ATS-1 and Portable One now available

AP is pleased to announce that accredited calibration is now available for ATS-1 and Portable One. Calibration for the 2700 Series, APx Series and ATS-2 has been available since January 2007.

Calibration provides documented and traceable verification that instruments meet or exceed all of their published specifications. Accredited calibration adds a further degree of rigor to the testing process, incorporating review and accepted Quality System Documentation as well as an On-Site Assessment including Measurement Audit and a Corrective Actions Cycle.

The Audio Precision Factory is accredited by the American Association for Laboratory Accreditation under ISO/IEC 17025:2005 for equipment calibration at our main factory in the USA.With its 17025 accreditation, the AP Factory meets the highest standard of calibration performance.

New instrument calibration

• All new ATS-1 and P1 instruments bought after February 15, 2008 are calibrated before shipping at no extra charge to the customer.
• A Calibration Report and Calibration Certificate are included with each instrument.

Calibrating Instruments already in the field

• All ATS-1 and most P1 analyzers in the field can be sent to the AP Factory or the European Service Center for calibration.
• Please contact your local Sales Partner for pricing. As with all service requests, please contact us BEFORE shipping your unit.
• We are sorry to report that some older P1’s cannot be calibrated. If you have a P1 with a serial number lower than 40,000 please check with AP Service for availability.

For more information, please visit the AP Calibration Services webpage at

http://ap.com/service/cal.htm

Sound Advice: Audio Test Q&A

Getting started with API Programming for the APx

Applications Engineer Eric Schultheis looks at the best practices for setting up an APx API programming environment.

This month we’ll offer some tips on writing automation scripts for the Audio Precision APx Series audio analyzers using Microsoft Visual Basic .NET. While APx500 Measurement Software has the most advanced audio measurement user interface in the world, sometimes the Operator needs a simplified interface (for example quality testing on the production line), or application-to-application automation is required. For these cases, APx has an comprehensive API (Application Programming Interface).

The basic idea here is to do as much as possible in the APx UI, save an APx project file, then use a VB.NET application and the API to open and run the APx project file, if necessary sending additional commands to the analyzer such as repeating measurements, skipping measurements (branching), or changing measurement settings.

Creating the APx Project File

Your first step is to create your test sequence inside the APx UI.

1. Open APx and create a New Project (File > New Project).
2. A default project has one signal path. To add more, go to Project > Add Signal Path, then use the Signal Path Setup view to define all the signal paths you’ll need for your DUT (Device Under Test.) In our example I have three: unbalanced analog, balanced analog and digital.
   • Best Practice: Give each signal path a unique name so it can be identified easily through the API.

Fig 1: The APX UI. Click to view full size

The second step is to add the necessary measurements to each signal path and configure them. Measurements cannot be added to a signal path through the API, so this work must be done in the UI. In my example, I have three measurements in each path: THD+N, Frequency Response and Crosstalk.

1. A default signal path has the Big 6 audio measurements. To add a measurement, right click on the Signal Path name and select the desired measurement from the dropdown menu. Note: It’s perfectly reasonable to have more than one instance of the same measurement, for example if you want to test THD+N at different frequencies.
   • Best Practice: Configure each measurement while you’re in the UI as it’s easier to set initial settings here than from the API. Unless directed otherwise, the API will always use each measurement’s settings as they were left when the project file was saved.
   • Best Practice: Like Signal Path, any time you’re working with more than one instance of a measurement, you should assign unique names: If the project file contains three measurements named “Frequency Response” within a signal path, any API call would only recognize the first instance of the measurement and would ignore the rest.
   • Best Practice: To simplify your workspace, delete any unused measurements from each signal path by right clicking on the measurement and selecting “Delete Measurement”. Keep in mind measurements can’t be added through the API, so only delete measurements you’re sure you will not need to access.
   • Best Practice: To minimize CPU overhead, turn off the signal monitors and click a non-updating measurement (such as a sweep) to select it. Signal monitors and constantly-updating measurements like Level require significant CPU resources, turning them off will free up those resources for other applications on your PC.  

Finally, we’ll save this APx project file as “My_APx_ Project.approj”

Running the Project with Visual Basic .NET

My objective is to create a simple application that opens the APx control software and has buttons to show or hide the APx GUI, open a specific APx Project file, and run the APx measurement sequence defined in the project.

AP provides a VB Express project template installer which gives you a starting point for a new APx VB project. The template creates a VB project with the APx class defined and a blank form. We’ll take this blank form and add the functionality we need by assigning API commands to buttons on the form.

Note: You can follow along by opening this tutorial's Visual Basic solution file

1. First, I’ll open Microsoft Visual Basic 2005 Express Edition and launch the AP API project template by clicking File>New Project> Installed Templates> APx500 Application. (Instructions how to install the AP template into your VB Express template library are here:  http://ap.com/products/apx_programming.htm#3)
2. Once the template has loaded, double click “APxMainForm.vb” in the Solution Explorer tree control to launch the Design View. You should see a blank Windows form. Double click on the form to enter the code editor for the form.
3. Use the VB interface to add three buttons to the form. You can do this in the code view or in  the design view. Please refer to the screen shot below or the tutorial sample project for syntax. 

• Button 1 toggles the APx software visibility using the APx API command APx.Visible
• Button 2 loads the APx project file using the APx command APx.OpenProject
• Button 3 runs the measurement sequence and generates the report using the command APx.Sequence.Run

• • Best Practice: Add a try-catch statement for each event in the code. Adding a try-catch statement will stop the application you’re building from crashing if it encounters an error. The Try-catch consists of a try block followed by one or more catch clauses, which specify handlers for different exceptions (errors).

Fig 2. Code syntax. Click to view full size

Fig 3: The end result: a simple APx Interface

When you've finished coding, publish the project.

You now have a simple application with buttons to toggle APx visibility, open the My_APx_ Project file and run the sequence. For more functionality, simply build on this foundation with more API calls. The APx Resource disc contains several examples, download the APx Resources Disc and browse to the Sample Files directory.

Related Downloads

• Sample APx project file and VB.NET project corresponding to this tutorial http://ap.com/ap/download/apx_programming_tutorial.zip
• The APx Resource Disc contains API Help and the API Browser http://ap.com/ap/download/APx_Resources_4th_Edition.zip
• API Training PowerPoint slides by AP Engineer Ken Ostrin http://ap.com/ap/download/API_training.pdf
• APx500 v2.1 control software (demo mode available) http://ap.com/software/apx_software.htm
• VBExpress “New APx Project” template installer for APx API developers http://ap.com/ap/download/APxVBExpressSetup.zip
• Visual Express 2005 -- Download from Microsoft http://www.microsoft.com/express/2005

Test Results: AP News & Events

AP Sales Partners of the Year

Every year, AP highlights one of our American, Asian and European Sales Partners as Sales Partner of the Year. As Dave Schmoldt noted last month, 2007 was another record year for Audio Precision, and every one of our Partners across the world worked tirelessly to help our customers, however the Partners below each went the extra mile.

Sales Partner of the Year is not just about sales volume, but also takes into consideration the investment each Partner makes to guarantee high quality service to our customers.

With all that in mind, we are pleased to present the 2007 Sales Partners of the Year:

• USA – WAVNet, Inc WAVNet, owned by Greg Groeper, is the AP representative for the Midwest/ Great Lakes region. Greg has been AP’s rep since 1985, and in that time has been instrumental in providing audio solutions to customers from Madison to Chicago. He is also great at tradeshows.
• Asia -- AP Technology AP Technology, owned by Man Li, is AP’s exclusive distributor in China, one of our biggest markets. Man Li has a very talented team of applications engineers who support AP users writing custom programs, translating manuals, and coming up with creative solutions to the toughest audio test problems.
• Europe – RTW GmbH & Co.KG RTW is AP’s distributor in Germany. RTW’s presence in the audio test market has grown significantly in the past year, seeing particular success with the APx586 16 channel analyzer while investing heavily in service. AP is also happy to welcome RTW’s new manager Andreas Tweitmann to AP, and we are very happy to see he is continuing the tradition of strong & knowledgeable service started by Renate and Rudolf Twelker.

 

UPCOMING EVENTS

NAB Show 2008 | Las Vegas

April 14-17

Visit the show websiteAES Europe 2008 | Amsterdam

May 17-20

Visit the show website

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