I have a recording setup consisting of an iMac running Presonus Studio One Pro, version 3. I use a pair of Firestudio Project interfaces that are daisy-chained. Connected to the last interface in the chain are two firewire external drives. Both drives are bus powered. One is a Glyph Portagig50 and the other is a Mercury SSD firewire drive. The problem started when I daisy chained the interfaces. I noticed drive noise coming through the interface and appearing in all my monitors the most prevalent being the JBL monitor I use during rehearsals. After upgrading to a better firewire cable, which had no effect I searched for any kind of a filter for firewire. I came across Sound Devices XL-1394 Firewire Power conditioning cable. It is specifically designed to reduce electrical noice from bus powered drives. It was hard to find one as they are no longer being manufactured but as luck would have it I found one on E-Bay. I just connected it and the noise is gone.
