Fedora, Linux

Better Bluetooth sound quality on Linux

Over a year ago I got my first serious Bluetooth headphones. They worked with Fedora well, they paired, connected, sound was directed to them. Just the sound quality was not overwhelming. I learnt that because of limited bandwidth of Bluetooth a codec with audio compression has to be used. There are quite a few of them to pick from: AAC (very widely supported because it’s the only one iPhone supports, partly freely available), AptX (also very widely supported, but proprietary), AptX-HD (enhanced AptX with a higher bitrate, also proprietary), LDAC (probably the best codec available, highest bitrate, available in Android, supported mostly by Sony devices), MP3 (also possible, but supported by virtually no devices). And also SBC which is a native Bluetooth, first generation compression codec with rather bad sound quality.

My headphones supported SBC, AAC, AptX, AptX-HD, LDAC, so all the advanced codecs. Sadly on Linux it fallbacked to the basic SBC because no other was available for Bluetooth, and headphones for €200 produced rather underwhelming sound. I mostly listen to music on Spotify. Listening to it on my headphones meant transcoding OGG 320 kbps to SBC and losing a lot of sound quality.

Then I recalled that Sony released LDAC as open source in the Android Open Source Project. And they really did because you can find libldac released under Apache 2.0 License there. So it could possibly be made available on Linux, too. Bluez was also able to negotiate LDAC with the end device. What was missing was a plugin for PulseAudio that would utilize the codec and encode the stream into LDAC before sending it over Bluetooth to the headphones.

Today I learnt that such a plugin had been finally created.  And besides LDAC it also supports AAC, AptX, and AptX-HD. Those are patent-protected codecs and the plugin relies on ffmpeg to support them, so it’s not likely they will be available in Fedora any time soon. But libldac is already in Fedora package review and is waiting for the final legal approval. The plugin currently depends on ffmpeg, but if it were made optional, we could at least ship LDAC support by default in Fedora Workstation.

I thought we could also support AAC because its decoder/encoder is already available in Fedora, but I learnt that it only supported the original AAC format while what devices support these days is HE-AAC which is still protected by patents.

Anyway, someone already built packages of both the plugin and libldac and I installed them to test it. And it worked on Fedora 29 Workstation, LDAC was used for Bluetooth stream encoding:

ldac

I don’t have bat ears, but I could recognize a difference in sound quality immediately.

If I’m not mistaken it makes Linux the first desktop system to support LDAC. And with support for other codecs it will make it the OS with the best Bluetooth sound quality support because all other systems support only a subset of the list, hence fewer headphones/speakers at their best sound quality.