A2DP

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A2DP ( Advanced Audio Distribution Profile ) is a Bluetooth profile and a multi-vendor technology, which allows stereo - audio signals wirelessly via Bluetooth to send to a corresponding receiver. One distinguishes between:

  • Sources (Sender) ( A2DP-SRC: Advanced Audio Distribution Source) and
  • Sink (receiver) ( A2DP-SNK: Advanced Audio Distribution Sink).

A source can be, for example, a Bluetooth mobile phone that sends audio signals to a Bluetooth headset or to a car radio (receiver).

The permitted transmission format of the audio files is defined in the A2DP specification. It is imperative that A2DP defines the so-called SBC codec for the transmission of audio data. MP3 is an optionally supported codec, as is AAC and aptX . For this reason, devices usually transport the data in SBC format.

This profile is often used in conjunction with AVRCP in order to be able to control the source remotely.

Operating system support (source only, not sink)

  • The A2DP protocol is natively supported from Windows 8 and newer.
  • On the Mac, A2DP has been natively supported since Mac OS X Leopard . In addition to SBC, AAC and aptX are also possible for transmission.
  • Android supports A2DP since version 1.5.
  • iPhone and iPad support from operating system version iOS 3.0 A2DP. SBC and AAC are supported.
  • Also, Windows Phone 7 supports Advanced Audio Distribution Profile A2DP + AVRCP 1.2 1.3.
  • Nokia also supports the A2DP connection standard in many of its devices with its own Symbian operating system .

Quality of the audio transmission

According to the standard, A2DP sources only need to support lossy SBC coding , which can be used without a license. Therefore, many device manufacturers shy away from the additional support of alternative encoders such as MP3, AAC or aptX. If both devices do not support the same alternative format, the user's music, which is usually stored in compressed form on the sending device, must first be decompressed and then compressed again with the SBC algorithm for the Bluetooth transmission. In theory, this can result in a loss of sound quality ( generation loss ). The possible bit rate of the SBC coding is, however, very high at up to 345 kBit / s, so that the loss for devices that also use them is in the inaudible range. If the AptX codec is used, which is not supported by all devices, the quality is on par with the CD manufacturer.

More recent developments for codecs with higher bit rates and potentially better sound quality are

  • AptX-HD (24 bit, 48 kHz, 576 kbit / s),
  • LDAC (24 bit, 96 kHz, 330/660/990 kbit / s) and
  • LHDC (24 bit, 96 kHz, 900 kbit / s)
  • UAT (24 bit, 192 kHz, 1200 kbit / s)

Finding suitable pairs of devices for the transmitter and receiver is quite difficult, as only a few manufacturers support more than one of the further developed codecs.

Individual evidence

  1. ↑ iPhone A2DP - Is the technology available on the iPhone? May 7, 2018, accessed February 23, 2019 .
  2. ↑ Bluetooth Accessory Design Guidelines for Apple Products (PDF; 279 kB)
  3. ↑ Bluetooth profiles supported by Windows Phone. microsoft.com Article ID: 2449475 October 4, 2011
  4. ↑ SoundExpert - Results Encoders 320+ kbit / s. Retrieved June 8, 2013 .
  5. ↑ AptX product page of the manufacturer. Retrieved February 8, 2015 .
  6. ↑ Qualcomm® aptX ™ HD Audio. Retrieved April 23, 2019 .
  7. ↑ New Bluetooth® technology for wireless high-resolution music - Sony UK. Retrieved April 23, 2019 .
  8. ↑ What is LHDC - hwa audio. Retrieved April 23, 2019 .
  9. ↑ HiBy W5 - 192KHz Bluetooth audio breakthrough. Retrieved March 9, 2020 .