そうだ・といわれている: the difference
そうだN3
Meaning
I heard that, It is said that
Past papers
Tested 4 times in past papers
Example
美味しいそうだから、たくさん買った。
I heard they taste good, so I bought a bunch.
といわれているN4
Meaning
It is said that, Is known as
Past papers
Example
危ないと言われているので、しないほうがいいよ。
Because it is said that it is dangerous, you shouldn't do it.
How to tell them apart
Unlike hearsay 「〜そうだ」: 「そうだ」 usually comes from a specific source, such as 「今朝のニュースによると」 or 「田中さんが言っていた」. 「といわれている」 has no particular source; it is something that has long circulated in society.
Forms: after a な-adjective or a noun the plain form often keeps 「だ」: 「安全だと言われている」.