Hey, I'm a big fan of cheap cable, as long as it does its job properly. The Radio Shack Gold Series cable that I use is reasonably transparent. It doesn't do too much harm to the signal.
The dock's performance got a bit better when I disconnected it from the computer. The headphone out also improved: docked and undocked performance is now the same with the dock unplugged. The dock's line out works without getting power from the computer, so I didn't think that a dock to RCA cable would do better. I thought that the universal dock could be such an adapter itself.
The dock cable that I want has the video connector. I haven't found a cheap one in stores so I borrowed a dock-to-RCA cable that has just audio. It's a cheapie Nyko Stereo Link
. The manufacturer claims that it's a distortion free alternative to the headphone jack. Its distortion level wasn't bad to begin with. Naturally, I wanted to verify their claim, especially with the new version of RMAA that was released just two days ago.
This time I set the volume level for the headphone out to two notches below maximum, so that 0 dBFS doesn't clip, even if the test doesn't at max volume. The volume control on the iPod doesn't change the signal level on the dock-to-RCA cable. So it already behaves differently from the universal dock, where the volume control does affect line out. A full-scale tone produces about 0.9 Vrms output, so it's not as hot as the headphone jack at maximum volume. It does not clip a full-scale signal. Here are the results:iPod headphone output vs. Dock to RCA adapter
Overall, it's pretty good. It does
have lower THD than the headphone out, but not by much. But look at the stereo crosstalk! It's still not shabby. The conductors on the iPod dock connector are very closely spaced. Even though we're not dealing with untwisting in CAT5 cable, or the high frequencies where near-end crosstalk would be more of a problem, maybe the cable can still make stereo crosstalk worse and a better cable could help. Or maybe the problem is the iPod itself. Either way, I doubt that you could tell them apart when listening to music normally. I didn't hear any big differences.