Background

In Bluetooth technology, Audio/Video Distribution Transport Protocol (AVDTP) uses Advanced Audio Distribution Profile (A2DP) for streaming audio in stereo. The A2DP encompasses compression techniques to reduce the amount of radio frequency bandwidth required to transmit audio. In addition to A2DP, Audio/Video Remote Control Profile (AVRCP) controls certain functions of the sending device such as pause, play, next track, etc.

All Bluetooth products using A2DP are required to implement audio encoding and decoding using low complexity Sub Band Coding (SBC) that supports up to 345 kb per second bit rate for stereo audio. The SBC codec has some issues though. SBC coding and decoding produces some undesirable artifacts in the audio signal. In addition, the SBC encoding and decoding cycle introduces a time lag in the audio. To improve on SBC's artifacts and time lag issues, a CSR proprietary codec that is called aptX® is implemented on some Bluetooth products.

During the negotiation phase, both Bluetooth devices handshake and they automatically discover the best codec and the highest bit rate to use for audio. If both devices support aptX, it is used rather than the default SBC.

The AES software helps identify audio issues in Bluetooth protocol by highlighting information, warnings, and errors related to audio data, codec used, and Bluetooth protocol implementation. They are collectively called “events” in AES.The AES window shows audio data plotted as PCM samples versus time in the Wave Panel. The audio data, codec, and protocol events are also graphically displayed in the Wave Panel, and with a single click on an event, engineers and testers are brought directly to the exact packets or frames related to the event in the Bluetooth protocol trace in the Frame Display. This helps users find issues quickly and easily. The events are shown time aligned with both the actual audio waveform and bit rate variances graph in the Wave Panel. The bit rate variance graph shows the average or actual amount of Bluetooth audio data sent over a period of time.

AES can operate in two modes: 1) referenced mode, and 2) non-referenced mode. In referenced mode a Frontline provided audio test file is streamed between the Devices Under Test (DUTs). The test file content and parameters are known to the AES software that performs a comparison for deviations. This process helps the software accurately detect anomalies created by the streaming process. In non-referenced mode DUTs stream audio of unknown content, limiting the types of detectable events. The software automatically determines the operation mode with no user input required.