allowed error: indices of omittable channels
2.5:  49, 50
5.0:  48, 50, 52
7.5:  15, 34, 35, 48, 49, 50, 51, 53
10.0: 15, 19, 34, 35, 48, 49, 50, 51, 53
12.5: 15, 19, 33, 35, 37, 47, 49, 50, 51, 53
15.0: 14, 16, 19, 33, 35, 37, 47, 48, 49, 50, 52, 53
17.5: 14, 16, 19, 21, 33, 34, 35, 36, 47, 48, 49, 50, 51, 53
20.0: 14, 16, 19, 21, 24, 25, 33, 34, 35, 36, 47, 48, 49, 50, 51, 53
22.5: 14, 15, 19, 20, 24, 25, 31, 33, 34, 35, 36, 47, 48, 49, 50, 51, 53, 54
25.0: 14, 15, 18, 20, 24, 25, 31, 33, 34, 35, 36, 38, 47, 48, 49, 50, 51, 52, 54
27.5: 14, 15, 18, 20, 24, 25, 31, 33, 34, 35, 36, 38, 47, 48, 49, 50, 51, 52, 54
30.0: 13, 14, 15, 18, 20, 24, 25, 31, 33, 34, 35, 36, 38, 47, 48, 49, 50, 51, 52, 54