10-02-2020, 08:08 AM
It turns out there's a bug in Lollypop affecting the frequency response. Please disregard the above ones and look at these instead (with hopefully more useful axis scales).
Massive distortion starts at about 8.5k and is clearly audible.
-24dB on the headphone amplifier doesn't make much of a difference (adjusted levels).
-24dB on the headphone amplifier in addition to -3dB on DA0 and DAC makes a huge difference.
Separate testing (earlier measurement so levels are slightly different) points to DA0 being the culprit. -3dB on DA0 alone makes the frequency response pretty much flat aside from the very high range above 15k and even then it's off by less than 1dB.
I think -3dB on DA0 is an acceptable workaround for the current hardware when used as a line out. I have yet to test this under any significant load so the dynamics with actual headphones attached are still unknown.
Massive distortion starts at about 8.5k and is clearly audible.
-24dB on the headphone amplifier doesn't make much of a difference (adjusted levels).
-24dB on the headphone amplifier in addition to -3dB on DA0 and DAC makes a huge difference.
Separate testing (earlier measurement so levels are slightly different) points to DA0 being the culprit. -3dB on DA0 alone makes the frequency response pretty much flat aside from the very high range above 15k and even then it's off by less than 1dB.
I think -3dB on DA0 is an acceptable workaround for the current hardware when used as a line out. I have yet to test this under any significant load so the dynamics with actual headphones attached are still unknown.
