Notes from the Test Bench
By Bruce Hofer, Chairman & Co-Founder, Audio Precision
After an excellent kickoff at AES London, I’m very happy to report that the APx515 is being extremely well received around the world.
Since its launch, we’ve given one-on-one demos of its capabilities to engineers from over 40 companies. For some (notably a few dyed-in-the-wool System One and System Two users), it’s the first time they’ve seen an APx: The automation and UI improvements we’ve created since APWIN have definitely made an impression. The best report I’ve heard is that people who may not have considered any audio test in the past can see the return on investment when the right instrument with the right features is presented.
Personally, I’m very proud that we have delivered this level of performance within the constraints of such a low price point. It took some time and creativity to squeeze those extra dBs out of less expensive circuitry, but I believe we achieved our objective. Of course, we had the advantage of starting with the most advanced audio measurement platform in the world. The team did an excellent job, and I believe the 515 will be seen as a significant milestone for our industry.
Output: Auxiliary Digital I/O Control
Automation can bring speed and cost benefits to most any audio test application, so it’s essential that an audio test system include extensive automation capabilities. Not only factory production lines, but also R & D departments and service centers can benefit—using an analyzer with a modern, measurement-oriented software interface, it can be easy to automate tests that are repeated even just once, in order to save time and guarantee absolute repeatability.
Automation is an extensive topic, so we’re going to focus on just one aspect in this article: Auxiliary Digital I/O (also known as General Purpose Input/Output, or GPIO).
Both the APx Series and the ATS-2 analyzers have 8 bits of auxiliary input and 8 bits of auxiliary output on the rear panel. The 2700 Series also includes auxiliary I/O capability, but requires the separate DCX-127 accessory for control through the user interface. The DCX-127 has 21-bit I/O, plus an additional 4 banks of 8-bit digital outputs. While all the instruments let you set and read the Aux I/O manually in the user interface, the real power comes through automation.
You can also configure the Aux Output to change state depending on whether a test passes or fails:
At any point in a sequence, you can add an Aux Input or Output control step. The following step pauses the test sequence until a microswitch senses the presence of a module in a test bed.
This Aux Output step sets the DSP on the device under test to its maximum compression mode, needed for the measurements that follow:
Programming Aux I/O
If the provided port count isn’t enough, there are PC based digital I/O cards available from numerous vendors. As long as an interface to .NET is provided (for the APx Series), or Visual Basic (for the 2700 Series and the ATS-2), they can easily be incorporated into an automation scheme. Additionally, if a command line interface is available for setting ports, they can be used with the APx sequencer.
Each Aux Out port can tolerate up to 20 Vdc and can sink up to 250 mA. If you need to sink more current, or need logic inversion or supply and ground isolation, you should add the appropriate components between the APx and the device.
Sound Advice: AP Knowledge Base
Remote Control of Consumer Devices In APx500
Audio tests of playback-only devices like DVD, Blu-ray, and MP3 players can be cumbersome, because a lot of user intervention is required to play each specific test signal track. An excellent solution to this problem is a USB controlled infrared transceiver, which can automatically send remote-control codes to the device under test.
One such item that we’ve tested is the Tira USB IR Transceiver, available online from Home Electronics for about $49 (USD). The company provides a software development kit for programmers who want to create their own programs in C#.NET. However, to use the Tira with APx, all you need is the TiraCMD command line interface, which uses command arguments to control the Tira’s IR transmitter. APx500 has the ability to invoke command line programs from any step in a sequence, so the two are a good fit.
After installing its Windows drivers, you’ll need to train Tira to learn the IR remote codes for the player you wish to control. To begin, go to the Windows Start menu, select Run, and type:
This creates a new virtual remote control called “mydvd”, and puts the program in capture mode. A prompt will ask you to enter the name of a remote key, like “play” for example. Then, you’ll be prompted to hold the player’s remote control up close to the Tira and to press the respective key twice. Following this process, the Tira can learn as many of the player’s IR codes as you need.
Once the program has learned the necessary IR codes, the Tira can be used in an APx500 project. In the following example, we select and start playing track 2 on the AP DVD-1 Test Signals disc, and then make a measurement using the Signal Analyzer.
To set this up, right-click on the desired measurement in the APx navigator, and select Edit Prompts and Properties. Then click the Add Step button and select Program. This displays the Run External Program Step window. The figure below shows the filled-in dialog, including the necessary command line arguments:
These arguments say to transmit “2”, ”Enter”, and “Play”, with a 100 ms delay between each. The Wait for Program Exit checkbox is also checked, so that the APx sequence waits for the command to be completed before continuing.
Test Results: AP News & Events
APx500 v2.5 Service Pack
AP has released a service pack for the current APx software, v2.5. AP strongly recommends that all APx users download the service pack and update their software.
This Service Pack offers a significant speed improvement overall, adds functionality to several measurements (such as accepting DTS audio with invalid NUMBLKS values), and fixes some bugs identified in the software after release. Full details are available in the Readme.txt.
You don’t need the .NET framework version if you are doing an upgrade, and/or the computer running APx500 is connected to the Internet.
International Competition Update
Watching the World Cup is a great reminder of how international Audio Precision is. Our Partners are well represented in South Africa, though some are doing better than others. We’re working on an APx project that will sweep Vuvuzela amplitude vs. frequency of own goals and easy saves missed that should interest Danish and English customers.
Congratulations to Portugal, the Netherlands, Brazil, Slovenia, Switzerland, Denmark, Japan, and Germany. Commiserations to Australia, Spain, South Africa, and Serbia. Good result? Unlucky? South Korea, New Zealand, Greece, France, Italy, England, and of course the USA.
©2010 Audio Precision Inc.