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--- a/1000-hours/sounds-of-american-english/2.1.4-e.md
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@@ -1,6 +1,6 @@
# 2.1.4. `e`/`æ`
-有些词典，针对美式发音，常常会用 `ɛ` 标注 `e` 这个音。
+有些词典，针对美式发音，常常会用 `ɛ` 标注 `e` 这个音[^1]。
Some dictionaries often use `ɛ` to annotate the American English sound of `e`.
@@ -27,3 +27,5 @@ There are two key points to pronouncing `æ`:
其中，第一个要点相对更为重要。你可以多试试这两个词，*apple* `/ˈæpəl/`，*banana* `/bəˈnænə/`，并刻意把其中的 `æ` 拉得更长一点。
The first point is relatively more important. Try saying these two words: *apple* `/ˈæpəl/` and *banana* `/bəˈnænə/`, and try intentionally stretching the `æ` a little longer.
+
+[^1]: In IPA, `e` is actually pronounced more like `eɪ`, a front, closed, unrounded vowel, while `e` in CEPD is equivalent to `ɛ` in IPA, a front, open-mid, unrounded vowel.
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