bob prohaska  wrote:
> Has anybody noticed a material difference in audio quality between
> the headphone jack and what comes out of the HDMI port?
>
> Obviously, a display with a poor audio circuit can corrupt a good
> signal, but assuming the display is "good enough" does it matter
> which is used?

1. It's NOT a headphone plug because the output level is too low for
headphones. It's a "3.5 mm line output". You would need a headphone
amplifier.
2. The Pi has no audio chip (DAC). It uses a simple(*) filter circuit
controlled by PWM. Sort of a manual 1-bit digital to analogue conversion by
the CPU.
3. The analogue out sounds horrible. But, they improved the circuitry for
the Pi3 and greatly improved the driver at some point. With that, it sounds
pretty good. I don't know if the improved driver is now standard, I guess
it might by. To be sure, add "audio_pwm_mode=2" to /boot/config.txt
4. HDMI output is digital. Quality of the sound on that end depends on
where you plug it in.
5. You might (I do) still get some noise/hiss/beep even when using the
hdmi. Annoying when quiet, not noticeable by me even at low music level, so
I put up with it. Not sure of the source. Maybe the whole setup is not
grounded well, maybe the power adapter of the Pi sucks, maybe the lcd
display+control board I plugged on top adds noise.
6. I get perfect quality from a Pi Zero with IQaudIO DACzero board and a
good old cinch cable.

* Relatively simple. Discussion:
https://hackaday.com/2018/07/13/behind-the-pin-how-the-raspberry-pi-gets-its-au
dio/

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