> If you are recording stuff from your iPhone using the 3.5mm jack you are already suboptimal perhaps even to the bluetooth.
This isn't true at all, unless your hardware is legitimately bad. All but the worst cables and amplifier chains can carry a 20 kHz signal (again, we're talking audio here -- that's basically D/C to modern electronics) at better than the ~45dB signal/noise ratio needed by the ADC on the other side.
And bluetooth isn't in general lossless. If the codec sets match, it's theoretically possible to send a music file directly over an A2DP pipe, but in practice I find almost all audio gets re-encoded for the transfer. In my car, I actually get significantly clearer music with the jack than I do over bluetooth.
I've observed a lot of ground loop problems in cars with a smartphone connected to a stereo line input and also to a USB charger. Some of the USB supply return currents pass through the shield of the audio cable and nastiness ensues.
Cars are one of the worst environments for analog electronics due to massive interference from spark plugs (basically wide band RF emitters), along with bad power from the alternator and high currents through the chassis ground.
I don't know about the iPhone, but many portable devices use a class-D amplifier on the headphone output for battery life, and most class-D amplifiers struggle with high-frequency reproduction.
I agree most usages of bluetooth are not going to be good (hence why I said "perhaps"). However I have a Cambridge Audio DAC with a bluetooth adapter that does have aptx and A2DP support. Does it sound better than the straight 3.5mm? I think so but that is probably because I think I like (cringe) upsampling :).
Of course in the car everything sounds like garbage to me. I don't have the speakers nor the attention span nor the multitasking ability to notice it.
That being said interference is always noticeable.
This isn't true at all, unless your hardware is legitimately bad. All but the worst cables and amplifier chains can carry a 20 kHz signal (again, we're talking audio here -- that's basically D/C to modern electronics) at better than the ~45dB signal/noise ratio needed by the ADC on the other side.
And bluetooth isn't in general lossless. If the codec sets match, it's theoretically possible to send a music file directly over an A2DP pipe, but in practice I find almost all audio gets re-encoded for the transfer. In my car, I actually get significantly clearer music with the jack than I do over bluetooth.