Bluetooth

Bluetooth is a protocol allowing low power devices to communicate wireless.

With a nominal bandwidth of 3 Mbit/s (2.1 + EDR) it is not suit for bit perfect audio.

Due to this limitation it is not possible to send CD quality audio (16 bits/44.1 kHz) over Bluetooth without applying lossy compression.

 

A2DP

Most of the time the A2DP (Advanced Audio Distribution Profile) protocol is used for audio.

This profile limits the available maximum bit rate to 320kb/s for mono, and 512kb/s for two-channel modes.

 

It support the following Codecs:

SBC (subband codec) is mandatory.

MPEG-1,2 Audio
MPEG-2,4 AAC
ATRAC (Sony)
In essence high bit rate MP3 but vendors can implement their own protocols.

 

APT-X

A proprietary codec by CSR
As it is not a mandatory part of the standard you need both a sender and a receiver supporting this protocol.

It is a lossy protocol but said to improve sound quality compared with SBC

 

• Compression ratio: 4:1
• Word depth: 16, 20 or 24-bit audio supported
• Data rates: 60 kbps to 576kbps(16-bit 15kHz mono to 24-bit 48kHz stereo)
• Frequency response: 10Hz to 24kHz
• Delay: <1.89ms @ Fs 48KHz
• Dynamic range: 16-bit>92dB, 20-bit>112dB, 24-bit>120dB
• THD+N: -81.1dB (0.008%) (24-bit)
• Sample frequencies: 0-48kHz
• Auxiliary data: Embedded, sample rate dependent up to 1/4 Fs kbps
• AutoSync: Can re-establish connection in 5ms
• Bit error resilience: Up to 1:10,000

1. Bluetooth SIG
2. Bluetooth - Wikipedia
3. Optimally Using the Bluetooth Subband Codec - Christian Hoene and Mansoor Hyder
4. Bluetooth - palowireless
5. APT-X - CSR
6. APT-X - Wikipedia
7. APT-X - Hydrogenaudio