BT receiver and sender over I2C, bad quality

[peruf79]

Hi everyone
I have a small project to receive audio over BT and send it to 2 or more heraing aids. I found the code from Phil to do so. Actually I have two ESP32-DevKitC from Espressif and they are connected with the accordingly wires of I2C. As sender I have a mobile phone, as receiver a BT-speaker. I can receive the sound but very unstable (very poor quality). It is to say, that I have two little external antennas. I also tried to supply the devices with an external poweer supply (5V and up to 2A). The interesting thing: the current rises (mesured for 2 devices) up to about 320mA and falls down to 300 mA. At 320mA I have the sound for abot 10s and then it goes away for another 10 to 20s. I guess it's a hardware issue, but have no idea, what it can be. Can someone help me?
Many thanks, Peter

[pschatzmann]

I am confused: why would you need 2 ESP32.
Are you really intending to send audio via I2C ? This does not provide any flow control!

Test each step separatly to indendify to source of your issue. I suggest that you start with a regular A2DP Sink playing back the audio via I2S or the internal DAc.

You did not specify what OS your mobile phone is using. If it some newer Apple this might maybe be the source of our problem.

[peruf79]

Thank you for your reply. Perhaps I don't know enough about the ESP32, but I think an ESP32 can only connect to one device at a time via BT. That's why I used two ESP 32s. I chose I2C because I believe it's worse to convert the received BT signal to analog and then convert it back again with an analog-to-digital converter in order to send it to the hearing aids. Perhaps a quick word about the project: my two grandchildren each have a hearing aid on the right side and, as of this week, a cochlear implant on the left side. These are from different manufacturers and therefore cannot be connected via a BT connection to a cell phone, for example. That's why I had the idea of building a device that would forward the received cell phone audio to two or even all four devices. I will think again about how this could be solved, but I am very grateful for any tips.

[pschatzmann]

So if I understand you right your flow is Mobile Phone -A2DP-> ESP32 - I2C -> ESP32 -A2DP-> BT Speaker
Here is the challange with your architecture: There is not flow control, so you will automatically run into buffer over and underflows, hence the quality is bound to be bad since you are loosing data.

Alternatively you can try to throttle the sending and use and monitor a buffer on the receiving side which drives a resampler that prevents over and underflows.

In addition the needed bitrate is quite a challange: 44100 * 16 * 2 = 1411200 so you need high speed mode.

[peruf79]

That's right, that's exactly how it works. But is there a smarter solution?