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In the ComProbe software, the audio data is shown in the A2DP tab in the Frame Display, see Figure 6. The
frame 2839, which is the first audio frame, is identified as being aptX encoded because of the successful
codec negotiation. At this frame, the conventional audio data analysis methods do not show any issues.
Assuming the data is aptX encoded, the AES software passes it to the AES aptX decoder. However, the data
was not decoded.correctly and is marked as a bad aptX frame.On further analysis, the AES software discovers
that the frame is not aptX encoded but is actually SBC encoded. Frame 2839 begins with “0x9C”, and all SBC
audio frames begin with sync word “0x9c” as shown in Figure 6. The AES cannot solely rely on the sync word
to determine if it is a SBC frame. To confirm the suspicion, the AES passed the data through its SBC decoder,
and the data came out cleanly decoded.
The AES software not only showed that there is a problem in the audio data but also made it clear where the
problem is.
The Error that is identified by Event 4, the Severity red circle , is a codec event at Frame 2839 states
"Unable to process AptX data as extracted. It appears that SBC encoded data is being sent over this stream."
Figure 7 - Audio Expert System Error on Frame 2839: Data not aptX.
A.1.4 Conclusions
This case shows the value of Frontline's Audio Expert System. An error in the transmission of an audio stream
compressed using aptX was not easily detected in the protocol analysis using frames. While, in this situation
with audio streaming between a smartphone and a
Bluetooth headset, there was not a significant disruption
of the audio, but in playback using other devices there may have been a more significant interruption of the
audio streaming.
The smartphone manufacturer may wish to find out why aptX compressed audio contained SBC compressed
data in the stream. We can speculate that there may be an underlying problem with clearing stacks or
memory between streaming events. This investigation is beyond the scope of this paper.
If there is interest in the Audio Expert System as an expansion of your ComProbe Bluetooth analyzer contact
the Frontline sales at
sales@fte.com or visit our web site at fte.com .
Author: John Trinkle & Priyanka Gupta
Publish Date:27 February 2015
Appendicies TELEDYNE LECROY
Frontline BPA 600 Hardware & Software User Manual 295