当半音不属于该调，并且无调号时需要加变音记号。

They are needed when chromatic notes foreign to the key and not indicated in the key-signature occur.

youdao

当半音不属于该调，并且无调号时需要加变音记号。

They are needed when chromatic notes foreign to the key and not indicated in the key-signature occur.

youdao