AP - The Recognized Standard In Audio Test


PC audio systems span a broad range, from basic stereo soundcards found on $400 laptops, to external FireWire or USB 2.0 high quality 24 bit 8 channel surround sound systems. PC audio systems are in many ways similar to portable digital audio recorders in function and testing requirements, but sometimes present special challenges that require an audio analyzer of the highest quality, speed, and versatility.

One challenge often faced is optimizing the levels in the signal path. Many times there are separate level controls for recording and monitoring, making it difficult to find the right combination of settings. The new continuous sweep feature on the APx instruments is invaluable because it can measure 14 different parameters in less than 7 seconds. This makes it possible to quickly identify the best performance settings, as well as to see any anomalies, like poor response at certain fader settings. Other testing challenges include inaccurate metering, controls with coarse steps, non-standard operating levels, limiting or clipping before full digital level, and driver quirks.

It is important to test both the playback and the recording chains separately. Some PC audio systems have digital I/O, making access to the signals simple. For systems without digital inputs, it's easy to generate high quality wave file test tones with Audio Precision's Waveform Generation Utility. For systems without digital outputs, the recorded wave file can be played back on another PC with digital outputs. It's always best to put the test platform and the PC audio system on two different PCs, to eliminate any possible performance issues or software and driver conflicts.

Audio Precision's 2700 Series, APx585, and APx525 are all well suited for testing PC audio. In fact, Microsoft has exclusively chosen the Audio Precision 2722A analyzer for its Windows Vista Logo Program Audio Fidelity Test.

The APx585 features an easy-to-use interface and 8 channels of audio in and out. This is a distinct advantage for rapid testing of newer consumer PCs which can have 6 and 8 channel surround sound systems. The APx525 is a two channel APx with higher performance than the APx585 at a lower price.

The 2700 Series features state-of-the-art performance, can directly analyze wave files, and has the ability to analyze the electrical characteristics of digital outputs. With the addition of the SWR-2755 switcher, the 2700 Series can be automated to test multichannel devices.

Both the APx Series and the 2700 Series offer highly flexible programming for automated testing. In addition, the APx Series measurement software makes it easy to create automated testing procedures directly from the user interface, without writing any code.

Common Challenges

  • Professional audio interfaces and better consumer PC audio systems have digital inputs and outputs. Audio Precision's dual domain 2722, APx585/586, and APx525 can all generate and analyze digital audio signals. In addition, the 2722 can analyze the electrical characteristics of digital signals, to investigate, for example, the failure of a card to connect to another or to transmit over a long cable length.
  • Pro audio computer interfaces boast studio-quality mic preamps, and should be tested to the same standards. Consumer PC audio systems often have mic preamps with poor performance. On all AP analyzers, you can set the output impedance of the generator to present the proper source impedance for valid measurements.

Tips for Optimum Testing

  • Features like spatial processing, artificial surround, and equalization will significantly affect test results. These features should be disabled before testing.
  • The positions of the software mixer volume controls can have a big effect on audio quality. Optimal settings need to be determined before running tests to avoid noise and distortion problems.

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