In audio test automation, BBT heavily relies on Audio Precision series 2700 and its development environment. Rich audio processing libraries developed for this environment empower run-time and post-processing analysis of the obtained data, decreasing the role of a tester to minimum.
- Why Audio Precision?
- Analysis of Complex AP Generated Outputs - Stepping Up The Automation
- An Example of a Simple TV Audio Test Scenario
Audio Tests
For verification of devices audio performance, BBT solution uses Audio Precision series 2700 and its development environment. Audio Precision is used both as audio analyzer and signal generator, depending on the test. Being a two channel system, for the full automation of device testing and all inputs/outputs cross-check, additionally, SWR-2755M output switcher, and SWR-2755F input switcher by Audio Precision (AP) are required. Without the switchers, the tests are semi-automatic, prompting a tester to perform the switch manually.
If your testing relies on another AP system, System 2, or ATS - customization is feasible, since we are familiar with interoperability amongst various AP analyzers and development environments.
Below is an example of signal feeds for Digital TV (DTV) testing. Within BBT system, Audio Precision is seen as any other BBT device. If it’s connected to a PC running RT EXECUTOR, its Dynamic Link Library (DLL) is loaded upon start of the test application. Control Interface DLL connects AP device with the corresponding communication interface. For more information on how to make a BBT device driver see the reffering article.
Some of the audio tests require stream to be played from an external medium, usually PC. For this reason, audio streaming cards become part of BBT automated test, as separate BBT devices.
Dolby Digital Converter tests use the Dolby DP564 multichannel audio decoder to obtain the reference results required by DD and DD+ Certification procedures. Hence, control for DP564 is implemented in a dedicated DLL, as a separate BBT device.
AP device, running on Audio Precision 2700 development environment, takes over control upon reception of a buffered string interpreted as a command which needs to be executed. It can be any part of the audio test process which needs to be handled by Audio Precision device, and doesn’t need intervention of the control system – loading the test configuration or setting up the AP system to required state, generating signals, performing measurements, analysis of the obtained data, or update of the test reports. Upon the execution, AP hands the control back to RT- EXECUTOR control software.
Why Audio Precision?
In the audio/video world, it is crucial for result data to be trusted at face value. Audio precision creates technology that is unparallel in audio performance and functionality.
Its powerful equipment and development environment provide:
- Testing of all digital and analog interfaces
- Wide spectrum of measurements of audio signal quality
- Run time and post run analysis
- Various mechanisms for definition of expected results, limits, and areas of interest
- Automatic verification of signal quality based on previously set references and tolerances
- Capability for running, measuring and storing of referent values and outputs which device under testing needs to comply with
- Possibility for simple implementation and integration of libraries for dedicated signal analysis
- Creating graphic user interface (GUI)
- VBA enhances document reporting in Word or Excel documents
Work in Word within Audio Precision development environment is based on single document VBA. Word documents are prepared as templates, more or less complex depending on the way the results need to be presented. It enables reporting in any required form, administration of data on the tested device, environmental conditions, date and time, and the tester. Given this mechanism, any execution of your tests can be ready for certification at a licensing company in the required presentation pattern.
The concept is based on the substitution of the key words from the template by actual numeric results or graphics. Each Word document is usually used for presentation of results of a given feature or module/device under test. In BBT automated solution, a summary document is also created for a quick overview of the overall results and the course of the testing.
See an example of automatically generated test report (doc file).
Analysis of Complex AP Generated Outputs - Stepping Up The Automation
Sometimes the biggest challenge in automation of audio tests is interpretation of the obtained test results, especially graphic data. BBT has stepped up the meaning of automation having developed powerful libraries for graphic and post-run analysis of the obtained test results.
Singular measurement refers to AP measurement that produces one value as a result, like DC component of the signal, THD, SNR, and other values calculated by Analog Precision analyzer. Obtained values can be immediately compared against the expected value given in advance in a form of the reference and allowed areas of tolerance.
Complex measurement refers to all tests that produce output which is indented to be post analyzed either by a tester who approves the correct behavior of the DUT during test performance, or automatically by dedicated procedures. Results of these tests are usually presented in form of graphs. BBT automated solution implements various mechanisms for verification of graphic results decreasing the role of a tester to minimum.
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In case of complex measurements, where it is required to post analyze mainly graphic output, pass/fail criterion can be defined in different ways depending on what needs to be verified. There are a few categories of these analyses
- Analysis which require verification of all singular values to be within certain range - typical example THD measurement during frequency sweep where all singular values need to be below previously defined level, or FFT analysis which needs to isolate frequencies of expected strength, and the other parts of the spectra need to be below defined level.
- Analysis which require calculation of certain parameters from the captured graph - typical example Dolby Pro Logic II tests, steering time constants and crosstalk.
- Analysis of various waveforms compared against a referent waveform. For this purpose, dedicated procedures are put into force depending on the shape of the waveform.
Following examples describe some of the problems and techniques to automate the verification process.
Example 1
In this example, during transition period around t0 point, it is allowed that signal varies in its amplitude, while it is more important that after a transition period, measured signal behaves very close to the reference. For these purposes, a slope verification procedure which modifies the defined tolerance L to Lcomp according to an angle enclosed by a tangent on the slope in the given point and x axis, is implemented.
Example 2
In the above example, verification of the graph output can be performed by comparison of the two envelopes, of the captured and referent graph. The envelopes are obtained by filtering of the absolute values of the captured signals.
Simple TV Audio Test Scenario
In the following example, maximum output power test of a TV is performed with RF and FAV inputs, and Automatic Volume Leveling (AVL) toggled on/off.
The system contains of:
- PC station running RT EXECUTOR performing the test
- FLUKE signal generator used in FM GERMAN STEREO modulation, BG sound standard, video pattern COLOR BAR
- RC emulator
- Audio Precision (AP) device, used for maximum output power analysis, and signal generator during external input (FAV) test
- TV as Device Under Testing (DUT)
Active BBT devices during the test performance are:
- StringManager, the device used for communication with Audio Precision development environment
- AudioPrecision, implementing control for the AP device
- Fluke, as FLUKE54200 control device
- UART, control for the tested TV, or DUT
- Compare device, used for the overall pass/fail test evaluation
Test scenario
- StringManager buffers data for the AP device. The system first addresses the AP device with MacroRun command to initiate the reporting by launching a Word document with the test results. The document is filled with basic information, like model of a TV under test.
- StringManager buffers data to prepare initial setting of the AP device. In this step, the AP loads test configuration, and performs initial set ups, usually input impedance, and other DUT specific settings.
- Next commands address Fluke device to set the generator to the desired configuration – video pattern, and modulation.
- Initialization of the TV under test – power on, settings for volume, equalizer, balance, sound mode, spdif, AVL off, setting source to tuner. The TV under test tunes to required frequency. This group of tests ends with setting of loudspeaker volume to maximum for the required maximum output power measurement.
- The AP device performs measurement with RF input, FM GERMAN STEREO modulation and AVL off, and fills the test report document with the result data.
- The system addresses the TV to turn AVL on.
- The AP device performs the measurement with RF input, FM GERMAN STEREO modulation and AVL on, and fills the test report document with the result data.
- The system addresses the TV to turn AVL off.
- The system addresses Fluke and UART device to prepare the generator and the TV for an external input measurement on FAV input
- The AP device generates signals for FAV TV input, performs the measurement with AVL off, and fills the test report document with the result data.
- The system addresses the TV to turn AVL on.
- The AP device performs the measurement for FAV TV input, and AVL on, and fills the test report document with the result data.
- The system addresses the TV to turn AVL off.
- The AP device finishes by evaluating summary result of the testing, for all the tested scenarios.
- The AP sends the summary result to the system
- Compare device evaluates summary PASS/FAIL test result.
- The AP device sends the link of the obtained Word document with the test results for data-base administration.
- The system turns off the TV under test via UART device.
The detailed course of the testing, seen from RT-EXECUTOR control software perspective, is described in the following table:
