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Topic: Quality of SBC (SubBand Coding) in Bluetooth' A2DP (Read 22184 times) previous topic - next topic
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Quality of SBC (SubBand Coding) in Bluetooth' A2DP

Hi,

does anyone know about the quality of the SBC (SubBand Coding) codec which is used as mandatory codec in A2DP besides the optional mp3, AAC and ATRAC?

A2DP (Advanced Audio Distribution Profile) is part of the Bluetooth protocol suite. It is used to connect listening units such as headphones or active speakers to audio playback devices like mp3, CD players or music servers.

SBC is specified here in annex B. Test bitstreams as well as a binary reference implementation of decoder/encoder can be found here. It's stated that this codec is band on a proposal presented to 98th AES convention by de Bont, Groenewegen and Oomen in 1995. Does anyone know further details?

Regards, GW

Quality of SBC (SubBand Coding) in Bluetooth' A2DP

Reply #1 –
I'm not sure, but -- looking at the specification -- it looks worse than MPEG Audio Layer 1 (in terms of coding efficiency). Its quality may be acceptable if at least 50% of the max bluetooth bandwidth (max=768 kbps) for a 44 kHz stereo signal is used. (just a guess!)

The bit allocation (two options available) is backward-adaptive (directly derived from the scale factors) and does not follow any psychoacoustic principles. So there's not much room for optimization (at the encoder side).

The bit allocation routine named "SNR" (first option) is IMHO ridiculus. I'd rather prefer an LPC-like codec without any subband transforms. (Wavpack lossy for example)

just my 2 cents,
SebastianG

Quality of SBC (SubBand Coding) in Bluetooth' A2DP

Reply #2 –
Quote
I'm not sure, but -- looking at the specification -- it looks worse than MPEG Audio Layer 1 (in terms of coding efficiency). Its quality may be acceptable if at least 50% of the max bluetooth bandwidth (max=768 kbps) for a 44 kHz stereo signal is used. (just a guess!)
[a href="index.php?act=findpost&pid=285189"][{POST_SNAPBACK}][/a]



Well, this codec seems to be optimizied for low delay and computational complexity.

Regards, GW

Quality of SBC (SubBand Coding) in Bluetooth' A2DP

Reply #3 –
Quote
...does anyone know about the quality of the SBC (SubBand Coding) codec which is used as mandatory codec in A2DP besides the optional mp3, AAC and ATRAC?[{POST_SNAPBACK}][/a]

Going to add SBC codec to SoundExpert testing system. Pretest discussion is [a href="http://www.hydrogenaudio.org/forums/index.php?showtopic=41118]here[/url].
keeping audio clear together - soundexpert.org