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Old 03-27-2021, 01:53 AM   #1
Registered: Feb 2004
Location: US / EU
Distribution: Fedora 31
Posts: 206

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Seeking bluetooth adapter that transmits audio in and out (more complex than it sounds?)

I'm sure there's terminology for this that I'm missing, so please bear with me as I try to (painfully) describe the situation.

I record certain meetings with my team (everyone knows, everyone is on board with this, we like to keep a log with transcript that we can refer back to).

I am trying to implement a set up that uses some piece of hardware - the CellTap 4C. Link is at

I connect everything as I should (with the exception of the CellTap to computer - they provide a TRS-TRS wire, but I needed to use a TRS-to-TRRS wire so that Fedora recognizes the line-in/microphone. Otherwise pavucontrol says the microphone is unplugged. I've tried using HDAJackRetask and force recognition of the TRS-only wire, but I always get a 'resource is busy' message. So the easier solution is simply this TRS-to-TRRS wire).

Hence, I run a wire from my phone to the CellTap device, run my headphones to the CellTap device, and run a wire from the CellTap device to the computer to record the calls there. Technically, this works. However, everyone I call hears their own voice echoed, so much that this setup is unusable. This isn't anything shocking - whenever I use my wired headphones, I've had this issue where the person I'm calling hears their echo. I'm not sure why, and I've spent weeks researching how to fix this issue, to no avail.

To bypass this issue, I've replaced the wire that runs between the CellTap device and my phone with a bluetooth adapter; that is, I connect the bluetooth device and CellTap with a wire. I then connect the bluetooth adapter to the phone via bluetooth. The result:
  • No echo
  • Caller hears me fine, and I hear the caller fine
  • My computer records the caller's voice
  • However, my computer does not record my voice!

Because the computer has recorded both my voice and the caller's voice when the CellTap was connected to the phone directly by wire, I believe I can narrow down the problem to the bluetooth adapter.

I'm looking to confirm this suspicion, to extent it's possible to diagnose with my description, with someone familiar with how bluetooth works. Is it because the bluetooth adapter operates as either receive or transmit? If so, is there are device I could use that would transmit both sides of the call? Any other solutions anyone can recommend?

I've tried other options, like using a TRRS 1 male / 2 female splitter - male going into the computer, one female connected to the CellTap device, and the other female connected to another earpiece. in order to capture the audio that wasn't transmitted from the phone. Fedora didn't pick that up.

I'm attaching a picture of the device and wiring to provide context.

Thanks for any help!!!
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