AP - The Recognized Standard In Audio Test

Audio Precision has developed a full-featured LabVIEW driver for its family of APx500 Audio Analyzers. The APx LabVIEW driver is a collection of LabVIEW subprograms that enable users to access the functionality available in the APx500 Application Programming Interface (API) with a minimum number of programming steps, using high level LabVIEW-typical functions. Using the driver, LabVIEW users can quickly and efficiently develop APx applications with clean, concise LabVIEW code.

LabVIEW is a graphical programming language and development environment from National Instruments. It uses icons instead of lines of text to create applications. LabVIEW programs are called virtual instruments, or VIs, because their appearance and operation imitate physical instruments, like oscilloscopes, volt meters, or FFT analyzers. Since it was first introduced in 1986, LabVIEW has grown steadily in popularity, especially for data acquisition, instrument control, and industrial automation. Today, thousands of engineers and scientists around the world rely on LabVIEW for applications in test and measurement, process control, automation, monitoring, and simulation.

Figure 1  Production test block diagram in LabVIEW using APx VIs.

A key reason for LabVIEW’s popularity is the easy connectivity it offers to a vast range of test and measurement instruments. In addition to supporting all the common interface buses (GPIB, RS-232, USB, FireWire, Ethernet, etc.), LabVIEW instrument drivers are available for thousands of test instruments from hundreds of vendors.

LabVIEW and APx in Production Test

The APx500 software has many test automation features built in, including the measurement sequencer, customizable user prompts, lockable projects, and the ability to call external applications. Users that want to go beyond the built-in automation features of APx500 can take advantage of its comprehensive API. The API is built on the Microsoft .NET platform, allowing custom APx programs to be developed in any .NET capable language, including Visual Basic, C#, and LabVIEW. With the driver, LabVIEW users can easily create automated audio test procedures by making simple block diagrams with very little programming (Figure 1). And experienced LabVIEW users will be able to take advantage of LabVIEW’s feature-rich library of front panel controls and indicators to create intuitive and highly customized user interfaces (Figure 2).

Figure 2  Production test user interface (custom LabVIEW VI).

So, if in addition to controlling a high quality audio analyzer, you need to control instruments like programmable power supplies, function generators, video devices, RF generators, mechanical actuators, switches, etc., LabVIEW and APx make a great combination.

LabVIEW and APx in Research and Development

LabVIEW has thousands of mathematical and scientific functions available, including VIs for waveform generation, waveform conditioning (filtering, DSP, etc.) probability, statistics, and much more. It also has extensive graphing capabilities. Combine this with the APx LabVIEW Driver which greatly simplifies acquiring and accessing APx audio test data from LabVIEW, and you have a powerful R&D platform. For example, if you want to make polar plots of a loudspeaker’s directivity response, do custom calculations on the spectral peaks from a multitone FFT, or plot the spectrogram of a chirp signal (Figure 3), LabVIEW and APx are a powerful combination.

Figure 3  Chirp Spectrogram

There’s even a driver VI to get back all FFT points from all channels of the APx signal analyzer measurement. But be careful! The APx supports FFTs up to 1 million points in size, and with channel counts as high as 16 in the APx586, that can end up being a lot of data.