AP - The Recognized Standard In Audio Test

Every device that bears a Dolby or dts logo is required to go through a compliance test process to insure that it meets Dolby or dts technical requirements. Depending on the specific technology licensed, certifying the compliance of a device can involve hundreds of individual measurements. These measurements verify the correct behavior of a decoder including features such as bass management, dialog normalization, and bit exactness as well as signal to noise ratio, crosstalk, and other fundamental audio performance characteristics.

For both companies, Audio Precision instruments are the preferred choice: AP instruments are referenced throughout the certification manuals and both companies provide AP tests to help with the procedures. The tests are available from Dolby and dts to their licensees.

The normal test routine involves setting up test parameters, playing individual DVD or Blu-ray tracks from discs supplied by Dolby and dts, and recording the results of each test in a Word or Excel document. Even with the Audio Precision test files provided by Dolby and dts, running each test with a disc player as the source is very time-intensive.

"Hands-free" testing Blu-ray & HD audio over HDMI

The 2700 Series OPT-2711 Dolby Digital option allows real-time streaming of encoded audio, but is limited to 16 bit 5.1 Dolby Digital. APx can output a wide array of encoded high-bitrate test streams over HDMI, which makes testing more modern decoder devices such as surround sound receivers far faster and more convenient. With the APx generator stimulating the receiver directly, no DVD is required, so entire sequences of tests can be run without opportunity for human error (wrong track selection etc) or the introduction of compatibility issues with the source disc player.

APx project files are available for testing DVD players, Blu-ray players, AV receivers, and new High Definition AV receivers with HDMI, SPDIF, or multichannel analog in and out. Each project includes a battery of tests that mirror the tests specified by Dolby or dts. Prompts are provided where it is necessary to play a DVD or Blu-ray track (when testing disc players directly) or change a setting on the device under test. After tests are complete, a rich graphical report is generated automatically.

 

Common Challenges

• Certification is very time consuming and is prone to human error due to the large number of steps. For example selecting the wrong DVD track will cause (sometime subtle) erroneous results.
• Using third party devices (such as a DVD player) can skew results: was the error caused by the DVD player or the receiver?
• Not all measurements have published limits. Dolby and dts allow a range, but the acceptable values are confidential
• Running the project tests doesn’t guarantee certification by Dolby or dts—it just provides a high level of confidence.

Tips for Optimum Testing

• If there is a problem area, just run that test rather than going through the entire sequence each time.
• Keep in close communication with Dolby or dts throughout the verification process. They will provide detailed feedback based on your license application.
• Check compliance early and often, so that any necessary changes can be incorporated into the design at the soonest possible stage. Sooner is cheaper.
• Automate as much of the test as possible to ensure repeatability and reduce time and human error.