BiffsBizIt's actually very good. Their ER-4PT is rated at 85% accuracy (by themselves, so you know) and their best (the 4S) is rated at 92% accuracy. However, etymotic targets a pretty analytical, cold sound signature. The HF5's are a tuned a tad less aggressive which leads to a less accurate but a bit more of an enjoyable sound. The difference is very subtle though, they are still a tad treble focused and very very detailed.