Experience of using HTC One hands free bluetooth calls.
The phone pairs properly, transfers the phone book and call history to the car bluetooth system. When I use my car stereo to place phone calls, I can hear very well, but the people on the other side complain about the sound quality. Like there is some additional noise as well as the sound is distorted. As a side note, I didn't have this issue with iPhone 4 or Nexus 4.
When I switch to the phone speaker and microphone, the people on the line say the sound has improved dramatically.
Now, one friend suggested that it might be the noise canceling microphone. I am guessing, when I use the car stereo for making calls, I am using the microphones in my car and the phone is been used only to transmit cell data received via bluetooth. When I switch to phone speaker, then I am using the microphones built in the phone, and the noise canceling function works fine.
My 2 cents, what about if the noise canceling microphone doesn't turn off in car stereo mode, or any bluetooth mode. I think it should be disabled if the bluetooth function is used. In my case this would mean that there will be interference between my car microphones and the noise canceling microphone in the phone.
Is there a way to check it with further tests?