Can people testify based on recognizing someone's voice without seeing them (tevias eina dikala)?
See Chullin 95b-96a Rava says ...now I know Tevias Ayin is greater than a siman, for if not, how could a blind man be allowed to his wife (maybe it is not his wife, but he cannot see her), and how can any man be allowed to his wife at night [when he cannot see her, maybe it is not his wife], the answer is teviyas ayin of [recognizing their] voice.
Ketzos 81:13 from Chullin, (the continuation is:
אמר רב יצחק בריה דרב משרשיא: תדע, דאילו אתו בתרי, ואמרי: פלניא דהאי סימניה והאי סימניה, קטל נפשא - לא קטלינן ליה, ואילו אמרי: אית לן טביעות עינא בגויה - קטלינן ליה
However, he brings Rashi Sanhedrin 67a - if eidim are hidden and they hear someone being meisis others to avodah zarah, he is not put to death if they only identified the meisis through his voice. You need a light so the eidim can see the person's face (even though he doesn't see the eidim). Therefore Ketzos says tvias eina of kol does not work for dinei nefashos, and if ti doesn't work for dineo nefashos, it doesn't work for dinei mamonos either. Then he quotes Shiltei Giborim Sanhedrin Ch 3 (8a in Rif) that tevias eina of kol only works for issurim - to recognize your wife, for example - not for mamonos or nefashos.
Nesivos 81:7 argues and says for mamonos, tevias eina dikala does work because Bava Metzia 20 regarding Simanim, isur is stricter than mamon, so if it is accepted for isur it is accepted for mamon, but dinei nefashos needs re'iah and yediah. (It is pretty clear that recognizing someone through their voice is yediah but not reiyah.)
Meshoveiev Nesivos rejects this because if so, umdena should work - but it doesn't from the case where Shimon ben Shetach saw someone chase aperson into a deserted building and Shimon ben Shetach followed them in and found one man dead and the other brandishing a bloody knife and no one else in the building. Shimon ben Shetach knew the guy killed the other guy, but said "al pi shnei eidim yumas hameis" prevented him from killing him (what about the fact that there only would have been one witness - Shimon be Shetach himself; it does not say anyone was with him?). This is on Sanhedrin 37b. (Regarding umdena see Rav Elchanan koveitz shiurim 2:38) but, conludes the Ketzos in Meshoveiv Nesivos, we see we need re'iah mamash.
Now I'm not sure this Ketzos is right. In an umdena, we didn't actually see the murder or event take place in front of our eyes, we can only infer it. But in our case, the Nesivos is talking about where they hear it happening as it happens. That very well might be yedia without rei'ah, but it is much stronger than an umdena!
One very surprising nafka mina comes up according to this Nesivos in a case where we have yediah and it is sufficient for dinei mamonos but not for dinei nefashos. Haghos Ashri, Bava Kama chapter 4 says if Ruvein kills Shimon, even though he's put to death, he is chayav to pay his (probably Shimon's, but it probably depends on the machlokes on Makos 2b if kofer is dmei mazik or dmei nizak) value to Shimon's heirs, but because of Kam Lei bidiraba minei, Beis Din cannot force him to pay it. If Shimon's heirs grabbed the money from him we don't take it away from them. But in this case, where we are sure Ruvein killed Shimon because we hear Ruvein in the room with Shimon saying I'm going to kill you and we hear an attack and Shimon crying out and later we find Shimon's corpse, we have yedia, more than umdena! - that Ruvein did kill Shimon. But without actually seeing it, we cannot put Ruvein to death. So, Beis Din should obligate Ruvein to pay Shimon's heirs, because the yedia eidus is good enough for dinei mamonos, according to the Nesivos.