Bluetooth headphone audio quality

Factual Questions
1

I’m assuming (haha, I know) the following takes place in Bluetooth connected devices. Let’s say a Smart Phone and Bluetooth headphones.

  • The phone knows it is bluetooth connected, so the DAC conversion to its speakers is disabled.
  • The phone sends the digital audio to the headphones through Bluetooth (lossless)
  • The DAC in the headphone does the conversion that ends up coming out the headphone’s speakers.

If this is true, it is not the Bluetooth protocol that can introduction degradation, but only the quality of the DAC in the connected device.

2

That would be the flaw in the assumptions. Bluetooth audio isn’t lossless. Depending upon the exact stack in use you can get a variety of compression and bandwidths. But even the best current implementations do compress.

3

To add, there are lots of possibilities in Bluetooth audio. Almost all compress. The actual Bluetooth protocol itself allows for a wide range of audio to be carried. And in principle a lossless channel could be used. aptX Lossless, or AAC SLC for instance. The default mandatory codec is the SBC which is nothing special at all.

A prime part of the choice of codec is low computational complexity. That is the compression is easy and fast on a low power processor, and very easy to decompress or a very low power processor (ie inside you headphones.) This naturally results in compromises against more complex and thorough codecs when the same bandwidth link to the headphone is used. Also resilience against transmission loss is useful.

4

Thanks Francis. I had forgotten about the complexity of codecs, etc.