Referenced Mode
In Referenced Mode, the system operates in a “pseudo closed loop” test scenario where the user plays a specific Reference Audio file on the Source DUT. The Source DUT negotiates with the Sink DUT to determine the appropriate codec and audio parameters to use and will then process the Reference Audio file accordingly before transmitting the resulting audio via Bluetooth. The Reference Audio is a pre-recorded audio test file provided in the Frontline software installer.
The Sink DUT receives the encoded audio, decodes it, and processes it for playback. In parallel, the Frontline analyzer unit snoops the over-the-air signal between the Source DUT and Sink DUT and emulates the RF reception and decoding done inside the Sink DUT. The Audio Expert System™ automatically detects that a Reference Audio file is being received and then analyzes the resulting audio for deviations from expected parameters.
Referenced Audio files are protocol specific.
The following events are reported whenever the system is operating in the Referenced mode.
- Test ID Found
- Test Script Not Found
- Invalid Test Script
- Synchronization Lost
- Unexpected Frequency
- Unexpected Level
- Unexpected Duration
- Amplitude Fluctuation
- Unexpected Phase Change
- Clipping
- Excess Noise
- CVSD HF Level Too High
- End of Test
Reference Audio Test Files
The Reference Audio files are specific audio files that exercise the system so that audio impairments can more efficiently and accurately be identified and reported. The Reference Audio files are composed of a series of back-to-back and relatively short duration tones of changing amplitude, frequency, and duration.
The test files are stored on the users computer In the directory "\Frontline <version #>\Development Tools\Audio Expert Test Files\". For example,
Test_1.03_48kHz_16Bit_3Loops_2Ch.wav
Note: Reference test files are periodically updated. Shown here is an example. Files delivered with your latest Frontline software version may have changed. Contact Frontline Technical Support for information on the latest reference file versions.
The test files have a set of tones forming a unique Test ID that lets the ComProbe analyzer know that it is capturing a test file instead of an arbitrary audio stream. There is no need for special configuration of the ComProbe analyzer. The Test ID will have the identifier notation N.vv, where N = the file number and vv = a two digit version, for example 1.02.
Using the Test Files
The analysis of the received audio results in a series of Audio Events being reported by comparing changes in the received audio to expected changes of the Reference Audio, and reporting deviation events when they occur.
The system starts up in Non-Referenced mode, and is continuously looking for a valid Reference Audio file by measuring frequency and amplitude of the received over-the-air audio. Transitioning to Referenced mode requires the successful detection of a Test ID tone sequence of proper frequency, duration, and value.
Once the Referenced Mode state is achieved, the expectation is that all tones encountered will conform to the script identified by the Collected Digits (the “Test ID”). The system remains in the Referenced Mode state until either the end of test is reached, or a loss of synchronization occurs.
The synchronization of the received audio (from the Reference Audio files) versus the internal Test Script is achieved based on changes in frequency of the tones in the Reference Audio file. Frequency changes are used because this parameter is relatively immune to the configuration of the network.
For a comparison of reference mode detectable problems to unreferenced detectable problems see the table in the audio event type table.
The Test Script
The Reference Audio used for Referenced Mode testing is generated from scripts that define a series of audio segments. Each segment provides an audio tone parameters including frequency, amplitude, duration, fade in and fade out durations, and start time. The script is an XML file delivered with the Frontline software. This file is used during Referenced mode testing for comparison to the "sniffed" Reference Audio parameters of frequency, amplitude, duration, etc.
Below is a sample script table and the resulting sample Reference Audio .wav file. The generated .wav file begins with a Test ID that is used to identify the "sniffed" audio as a Reference Audio file, and the Audio Expert System™ automatically switches from Non-Referenced mode to Referenced mode.
| Segment | OpCode | Frequency | Level | Cycles | Duration | Fade in | Fade Out | Start Time |
|---|---|---|---|---|---|---|---|---|
| 1 | F | 200 | 0 | 5 | 0.025 | 0 | 0 | 0.000 |
| 2 | F | 1000 | 0 | 25 | 0.025 | 0 | 0 | 0.025 |
| 3 | F | 300 | -12 | 15 | 0.050 | 0 | 0 | 0.050 |
| 4 | F | 600 | 0 | 30 | 0.050 | 0 | 0 | 0.100 |
| 5 | F+ | 880 | -6 | 44 | 0.050 | 0 | 0 | 0.150 |
| 6 | F+ | 240 | -6 | 12 | 0.050 | 0 | 0 | 0.150 |
| 7 | F | 600 | -95 | 30 | 0.050 | 0 | 0 | 0.200 |
| 8 | F | 600 | 0 | 30 | 0.050 | 0 | 10 | 0.200 |
Referenced Mode Testing Processes
In the Referenced mode, the devices under test use a specific audio file (called reference file or test file) provided by Frontline whose contents are already known to the Frontline software. The software compares the parameters of the received audio data against its parameters and presents analysis for the user. Commonly, in Bluetooth technology the music sent via A2DP and speech sent via HFP. There are a few ways users can conduct referenced mode testing depending upon what profile they are using. The figure 17 shows the source of the audio and the medium through which it can be accessed by Source device to send to sink device via Bluetooth.
| Audio Source | Process to Send Using A2DP | Process to Send Using HFP |
|---|---|---|
| A file stored on the device’s local memory | Play the locally stored file on the audio source device | Play using the third party App that transmits music data on HFP. |
| Streaming audio over a cellular network |
Play the test in a browser on the audio source device |
Make a call to 434-964-1407 or 434-964-1304 through a cellular network. The phone number receiving the call playbacks recorded test signal. |
| Streaming audio over a Wi-Fi network |
Play the test in a browser on the audio source device |
Make a call to 434-964-1407 or 434-964-1304 through a VoIP provider such as Skype. The phone number receiving the call playbacks recorded test signal. Potential problem: The VoIP provider might use custom codecs and cause undesirable behavior. |
A2DP
Playing the test file locally
The simplest way to perform music data testing is to directly play the reference file from DUT1 to DUT2. To do that, save the reference file provided with the Frontline software on the Source device. Then connect the Bluetooth enabled devices and play the music file from one device to the other. The software will automatically detect the mode and present analysis for the user.
Playing the test file via Internet
If the user is testing a scenario where they need to analyze audio played through the internet (either using Wi-Fi or cellular data plan), they may access the reference file on YouTube provided by Frontline - https://youtu.be/rmirDbikrtM. Note that the software is only analyzing the Bluetooth link between the two DUTs. Any abnormalities at the Wi-Fi and cellular network level will affect the audio quality that may not be Bluetooth protocol related and the software will not be able to detect that.
HFP
Playing the test file by calling a phone number
Frontline provides the following phone numbers - 434-964-1407 and 434-964-1304 that users can call, to conduct speech audio data analysis over Bluetooth. The calls can be made using the cellular network (most common method) or VoIP. Again, the VoIP provider might use custom codecs and cause undesirable behavior which cannot be detected by Audio Expert System™ software.
Playing the test file using Third party Apps
Bluetooth Audio Expert System™ Reference mode testing can be accomplished using third party apps on Android, iOS, and Windows phones. The following apps are available from their respective App stores:
Note: When selecting and using these apps, thoroughly review all the vendor documentation. While Teledyne LeCroy has conducted testing of these apps, Teledyne LeCroy has not completed full interoperability testing with our library of Bluetooth devices and does not warrant the use of these apps with every device when using the following procedures. Teledyne LeCroy does not provide support or maintenance for third party apps. Any issues or questions should be directed to the app developer.
- In the following steps Device Under Test 1 (DUT1) is the device sending the reference test file to DUT2.
- Download the third party app to DUT1 and follow the app vendor's instructions for installation and use.
-
Load the Audio Expert System reference test file
"Test_1.02_64.1kHz_16Bit.wav"
on DUT1.The test file is stored on the users computer In the directory "\Frontline <version #>\Development Tools\Audio Expert Test Files\".
Note: Reference test files are periodically updated. Shown here is an example. Files delivered with your latest Frontline software version may have changed. Contact Teledyne LeCroy Technical Support for information on the latest reference file versions.
- With the
- Launch Audio Expert System by clicking on the Control window
. - Turn on Bluetooth on your DUTs, DUT1 and DUT2. Turn on the third party Bluetooth app for routing the reference file over A2DP or HFP by following the vendor's directions.
- Send the reference test file from DUT1 to DUT2 via the third party app.
-
Observe the events in the Audio Expert System™Events Table. Look for an event Description:
“TestIDFound : REF: Test ID 1.02, Channel Gain = -11.8 dB TermFreq=400.0”.
Note: This is an example. The display may vary with the reference file version.
The Frontline analyzer has successfully detected the reference test signal and the system is locked into reference mode.
Test Cases for Referenced Mode Testing
