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DAP with the best sound quality using Rockbox and IEMs?

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Llorean:
Are you asking anything? I've already said you won't hear it with those.

Christine Tham:
If you are truly interested in choosing based on objective sound quality rather than perceptions (unfortunately our ears cannot be easily trusted since they are quite adaptive), I second the recommendation to conduct RMAA tests. They are relatively easy to do, but require a PC with a reasonably good sound card, preferably a pro-audio sound card (but reasonably good ones start at around US$100).

However, RMAA doesn't tell the whole story. In my experience, jitter is a significant influencer in overall sound quality.

Unfortunately:
1. Jitter is not easy to measure. Some commercial test units are based on the J-test methodology proposed by the (late) Julian Dunn. Since the J-test does not actually measure jitter but artefacts potentially caused by jitter on a specific test waveform, some skeptics say it is not a true measure of jitter.
2. I suspect most portable players have poor jitter. I don't know if one player is better than another. John Atkinson has measured the jitter level on the original Ipod using a Miller test unit, and the results weren't that good (as I recall, several times higher than a good cd player).

My recommendation is to choose the top 3 players based on RMAA, then conduct extended listening tests to determine which one your ears prefer. Perceptually, the influence of jitter is on the "pace, rhythm and timing" of the music (PRaT). Have you ever wondered why some players sound more exciting and aggressive, others tend to sound laidback and relaxed ...? On some players, the drummer sounds precise and tight, on others a bit wooly? Even though the actual tempo is the same, our ears pick up other clues to determine our emotional response to music.

Llorean:
I hate to be pedantic here, but while trying to describe an objective issue, you've been very subjective in what jitter results in. As well. jitter in CD reading is often an issue with the actual reading. What phase are you particularly concerned with jitter in, communication with the DAC?

All you've done is basically said "jitter makes it sound bad." Where, exactly, would jitter occur on an MP3 player, and how much, exactly, is the maximum it could reasonably be expected to affect output in hard terms?

Febs:
Do we really want to get into discussions here about whether jitter is audible?

Llorean:
I was looking more for some math. Average percentage of lost and/or repeated samples, for example.

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