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Use case: I have an Audio Technica turntable that can send a digital signal out over bluetooth. I want to be able to sample and/or digitize records, over bluetooth.

When the turntable is in pairing mode, it doesn't show up as an available device to pair with on Ubuntu (or on my phone). I'm able to pair with other devices without issue,

The bluetooth audio stack (on ubuntu at least) appears to be set up as an audio transmitter, but not as a receiver.

As well as the UI tools (built in KDE ui around bluetoothd, and also blueman), I tried running bt-adapter -d, and then putting the turntable into discovery mode. In none of these cases is it even detected.

Are there lower level tools that can get at the negotiation, or is this restricted at the hardware level?

user717847
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  • Not sure what you are trying to do. You want to record audio from the turntable, but you are not able to connect to it? – ibuprofen Aug 22 '21 at 03:12
  • Personally I use `bluetoothctl` to connect and disconnect Sony BT headphones as the standard controls are very buggy and often do not manage to connect. In short I have a script where connect is `printf %s\n quit\n "$mac"` and disconnect is `printf 'disconnect %s\n quit\n' "$mac"` where `$mac` is the mac-address of the headset. I used to have to disconnect before connect, but tweaked some configuration files and now it connect normally. Beyond that the headset has various profiles: audio only, and two way audio mic - the latter gives useless sound. But not sure if any of this helps you. – ibuprofen Aug 22 '21 at 03:19
  • On first run one have to pair the devices. This can also be done by `bluetoothctl` – ibuprofen Aug 22 '21 at 03:20
  • @ibuprofen bluetoothctl is handy, thanks for that. But it doesn't show the turntable either. – user717847 Aug 23 '21 at 11:59
  • Sorry for being slow :P, but if I gather what you are saying correctly the issue is to discover and pair the turntable? Or are you able to pair but not connect? – ibuprofen Aug 23 '21 at 23:21
  • @ibuprofen no problem, I'm probably doing a bad job explaining -- yeah, it doesn't show up as a pairable device on my computer (or my phone). I made the assumption that it's looking specifically for a "receiver"/sink along the lines of a bluetooth speaker, which is why it isn't working. I don't know much about the bluetooth protocol or whether that's a thing though, so maybe there's something else going on. – user717847 Aug 25 '21 at 02:00
  • Yay. OK. Then I follow. Had a look at https://www.audio-technica.com/en-us/at-lp60xbt and it say it uses `aptX`. Then for `aptX` one are (partially) in trouble because it is proprietary. From some looking around you could read this https://askubuntu.com/a/1173550/828184 , https://ostechnix.com/turn-your-linux-pc-into-bluetooth-speakers-for-your-phone/ , etc. Perhaps you get something from it. – ibuprofen Aug 25 '21 at 02:57
  • Another option to test is Pipe-Wire. Have not tested it myself. https://wiki.archlinux.org/title/bluetooth_headset#Headset_via_Pipewire / https://wiki.debian.org/BluetoothUser/a2dp#AptX.2C_LDAC.2C_and_AAC_codecs_are_not_available_with_PulseAudio – ibuprofen Aug 25 '21 at 02:57
  • BT and audio in general is a nightmare lol. It's easy to mess up things, and often end up testing various things - so good to keep notes as one go. BT is not a protocol as much as a list of protocols i.e. https://en.wikipedia.org/wiki/List_of_Bluetooth_protocols and of course https://en.wikipedia.org/wiki/Bluetooth which can be an interesting read to at lest skim. – ibuprofen Aug 25 '21 at 03:08
  • Progress, I think. Following your links in your first answer, I was able to get the computer to show up as an audio sink for my phone, and to start audio from my phone and have it play over my computer headphones, using aptX. (It was mono only but other than that, so far so good.) Secondly, I was able to pair the turntable with a Beats bluetooth speaker (it happens more or less instantly) and verify that I could play audio over that link. However, I still can't pair the computer and the turntable; running bluetoothctl, the turntable doesn't appear as a device when scanning. – user717847 Aug 29 '21 at 19:56
  • One interesting thing is that I can't connect to both my phone and the bluetooth speaker at the same time from my computer - which seems weird, given that the phone is a source and the speaker is a sink. But whatever - that's not important to this use case. – user717847 Aug 29 '21 at 20:02

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