Reference for Rosh Hashanah 51:12

והא תנא מפני שהוא קרן קאמר חדא ועוד קאמר חדא דאין קטיגור נעשה סניגור ועוד מפני שהוא קרן

one reason is because the accuser cannot act as defender, and the other is because it is keren. What says R'Jose to this? - His answer is: Your statement that the accuser cannot act as defender applies only to the inner precincts, and this shofar is [used] in the outer precincts. And as for your statement that this shofar is keren, all shofars are likewise called keren.

Jastrow