AP - The Recognized Standard In Audio Test


If it's not being broadcast or streamed over the internet, content today is usually distributed on optical disc. Though various formats have come and gone, the three standards today are CD, DVD and Blu-ray.

Blu-ray is the latest optical disc format to be released since the CD debuted in the early 1980s and features support for a multitude of high definition multi-channel audio formats. Most Blu-ray Disc players rely on the HDMI digital audio/video connector to connect to TVs and receivers, though some of the higher end players also have analog audio and video.

The HDMI connector and the new formats require special capabilities in an audio analyzer. The Audio Precision APx585 with HDMI is the world's only Blu-ray and HDMI-capable audio analyzer. The HDMI option can accept all Blu-ray audio formats, including linear as well as Dolby and dts encoded audio, with up to 8 channels, 24 bits, and a 192 kHz sample rate. Additionally, linear and encoded files can be directly uploaded into the APx's generator.

The fundamental challenge to testing disc players is the lack of an input for the analyzer's test signals. The solution is to put test tones on disc. The analyzer must have the intelligence to recognize the tones and adjust to them automatically. Audio Precision's companion test signal discs for DVD and CD provide a complete collection of suitable test signals. The companion Blu-ray Test Signal disc contains a wide range of audio test stimulus signals in linear, Dolby, and dts formats.

Testing DVD players, which typically support six discrete audio channels, is also well served by the multi-channel APx585. CD player testing, or stereo testing of multi-format players, can be done with any of Audio Precision's APx Series or 2700 Series or ATS-2 analyzers.

If the SPDIF or TOSLINK stereo digital output is being tested, then an analyzer with a digital connection is required: the APx525, APx585, APx586, 2722 or ATS-2 are all appropriate.

Common Challenges

  • Not all Blu-ray players can play all audio formats. Some early players can't play formats that they claim to, or can't play them well.
  • A Blu-ray player that encounters a high definition encoded format it can't handle will revert to the core audio format (basic Dolby Digital or dts Digital Audio). Many players don't indicate when they are reverting to the core audio format.
  • High frequency distortion is missed with traditional THD+N and SMPTE IMD tests. The twin-tone (DFD) IMD test, available on the APx and 2700 Series, will reveal high frequency distortion missed by the other tests.

Tips for Optimum Testing

  • Standard CD and DVD test discs, published by a number of companies and standards organizations, can also be used. Use these in addition to the test signal discs published by AP.

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