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BOOST-CC2564MODA: A2DP Volume Discrepancy based on which device connected to BT (I2S/PCM)

Part Number: BOOST-CC2564MODA

I have the bluetooth setup (BOOST-CC2564MODA + MSP432P401R) connected to an external speaker via a digital amplifier. The amplifier is configured the same way during both tests. When I plug the I2S from my laptop directly into the amplifier without bluetooth, I can play a sine wave and get max output power with no distortion at 100% volume, but would likely distort if I pushed it past that.

However, depending on whether my phone or laptop is connected to the Bluetooth system setup, I seem to be getting different volume outputs causing distortion, pushing the speaker harder than without bluetooth causing distortion. I've checked the I2S on the speaker input using a protocol analyzer and it looks like the offset is correct on both, but the Laptop (connected via bluetooth) seems to send a much hotter signal and will clip/distort my speaker sooner. 

My main question is this: is there something volume related in A2DP that is changing the volume output digitally? I don't fully understand how it's able to push the amplifier so differently based simply on the digital input. 

What should I try next? 

  • As it turns out, I had a discrepancy in the definition of offset. I had my amplifier reading the signal at an offset too far shifted to the right, giving it a much greater power.

    The discrepancy in the volumes between phone and laptop was due to the differences in the outputs of the files I was playing.

    I hope someone finds this helpful. 

    Thanks,

    Jackson

  • Hi Jackson, 

    We need few clarifications - 

    1. Can you try playing the same file through laptop directly connected to digital speaker and through BT connection and check if the volume levels are same? 

    2. the loudness also depends on the default settings in laptop and phone. This can cause the difference in the peak volume o/p

    Regards, 

    Sudharshan K N