I'm pretty close to my wit's end and would welcome any suggestions -- no matter how absurd or even repetitive -- from anyone who might have a clue about how to eliminate the interference. I know it's possible, 'cause I did record some good sample recordings with this exact equipment and set-up over the weekend. The big difference was that over the weekend, I was located in a fairly remote house on a river in a rural location, while now I'm located in a townhouse in a semi-urban location.
My setup: Microphone (MXL 990 Cardioid Condenser Mic) -> 3' mic cable -> mixer (Behringer Eurorack UB802 Mixer) -> tape-out cable (RCA -> stereo mini-jack) -> Griffin iMic -> USB -> Macintosh iBook SE (recording software: Audacity)
Downstairs, I wasn't terribly surprised to get the interference. The basement is a pit of potentially RF-emitting devices: everything related to my computer (printer, external hard drive, external cd burner, etc.), tv, stereo (and speakers), DVR, VCR, etc. I tried all sorts of settings on the knobs of my mixer and levels on Audacity. Listening to the signal through the headphones on the mixer, things sound fine. Listening to a recording, it sounds annoying.
I moved upstairs (3rd story) with only my mic, my mixer, my computer, and the necessary cables. I turned off my cell phone. I turned off the wireless card in my computer. I turned off the wireless router (located in the basement). I even turned off all the lights in the room (none of which was florescent). I pressed record, listened to the playback and heard the "dit-dit-dit-dit..." still there.
I'm going to try again, this time from the dining room and/or living room. Other than that I've run out of locations in my home. I'm really beginning to fear that there's RFI from my neighbors that's causing the problem. I hope that's not the case, 'cause I won't be able to do much about that. Otherwise, I might be able to find the offending source and eliminate or limit it.
Like I said, any suggestions are welcome. If anyone wants to hear samples of what I'm talking about (even if it's just out of curiosity), comment and I'll put some MP3s online later tonight or tomorrow.
[Update: More information about this problem and sample MP3s are included in another blog entry.]
[Update: More information: it's probably not the mixer.]