ESP32-A2DP as a Bluetooth bridge for YoRadio.

[HighWayManDenmark]

I have this idea to use a second ESP32 as a bridge between YoRadio (First ESP32) and my Bluetooth speaker.
First tried to add some BT-modules to YoRadio - the sound was terrible. When I got one source of noice solved, another took over.

Then I thought about - why not connect another ESP32 to handle the I2C data stream directly to Bluetooth sender. No DAC - no crappy BT modules.

Has anybody been on this path ?

Which version of this lib will be a good starting point ? Arduino or PlatformIO ? Do I need AudioTools ? Will it be a solid solution for hours of use ? Heard that the BT connection is more or less stabile... And most important - is the BT output on level or better than the sound I get from my Windows PC ?

Is there anything I need to address with this solution - buffers/memory/noice/stability...

Any starting info will be very much appresciated.

[pschatzmann]

Some people are struggeling with A2DPSource, so I suggest that you start very simple e.g. by just sending a data file to familiarize yourself with the potential issues.

You need to make quite a few decisions:

• do you plan to transmit pcm data or encoded data (for pcm, I2C is too slow)
• if the source has pcm data you might cosider to use a simple codec to reduce the amount of data: e.g. ADPCM
• is the data source asynchronous and you can just try to keep the receiving buffer filled or synchnonous and you need to implement some respampling to achieve the same thing because of the clock differences between the sender and receiver.
• What mechanism do you use to prevent buffer overflows or underflows: e.g. Seriial flow control

My recommendation would be to look into Serial with hardware flow control and to use a codec if the source only provides PCM data.
Please note, that you might need to resample or change the format, when the provided sample rate does not match the 44100, 2 channels 16 bit format required by A2DP.

I recommend that you always use the latest versions and use the tool that you are most familiar with.

[HighWayManDenmark]

Thanks for your answer.

As a newbe I have trouble understanding that I2C should be to slow...

In my current YoRadio I use I2C to send the stream from ESP to a PCM-module. Why is the same I2C to slow for sending the stream to an ESP acting just like a PCM-module ? When listening to an Internet Radio Stream latency is not an issue.

I'm realy trying to make a very simple setup using A2DP transmit to a well-known Bluetooth speaker. Instead of using a PCM and a crappy KCX-module - I want to use another ESP32 for this task.. I hope to avoid to transform the stream multiple times to have the data straight to the speaker. Will it be possible ?

[pschatzmann]

Not sure what you mean with PCM-module.

I2C supports a max speed of 1 MHz (1,000,000 Hz) = ~100,000 – 110,000 Bytes/s
A sample rate of 44100 stereo 16bit PCM audio data (for the A2DP source) requires (44100 * 2 * 2) 176,400 Bytes/s

I2C is usually only used to configure the codec and the audio data is trasmitted via I2S or SPI.

[HighWayManDenmark]

Ahhh my mistake - when I talked about transfer I wrote I2C but I should have written I2S.... Forgive me i'm just beginning to understand this...

[pschatzmann]

Test I2S-I2S first with two test sketches:

• streams-generator-i2s
• streams-i2s-i2s-2 or streams-i2s-serial

I tried a couple of years ago, but from time to time got some lost samples.
Maybe things have improved...

[HighWayManDenmark]

Thanks again - will test these sketches to verify connection.