Ok folks, this is going to be a bit of a novel, because there's a bit of detail to go into.
Short story is: I'm getting a lot of cell phone interference on about half of my recordings and I'd like to stop it, cos its ruining otherwise perfectly good recordings and driving me crazy. Any help would be appreciated.
I've read all the threads on this subject on this board, and almost revived an old thread but decided to create this one because the old thread hasn't seen a post for 6 months.
I suspect this is more of an issue for me than most of you lot because most of the cell phones in Australia are on a GSM network...I believe that's not the case in the US (pls correct me if I'm wrong).
First point to make is that the interference is not caused by my phone, which is off at all times during recording. The interference is from those lovely people around me. I've tested at home and am picking up cell phone interference from up to 10 meters away (I haven't tested any further than that).
I've run hundreds of tests using the following equipment in different combinations:
Mics: at943 bodies with at853 caps (mini xlr ends)...I believe the cable is standard (it has 'audio technica' written on it), but they're only 4 feet long.
Power: homemade 3 wire battery box (as per Grame Cogger's schematics) and Church Audio 3 wire bb / preamp
ADC / pre: AD20
Recorder: iriver H120 * 3 (yeah, I've tested on all three of 'em)
The tests werent terribly scientific, but I tried to be as consistant as possible...I basically recorded silence with different combos, placed a phone nearby, made lots of calls, and noted the levels in Asobe Audition before and during the resultant interference.
I won't post all the data, unless someone wants it, but what I've found most enlightening from these results is that a particular mic into a particular channel sees more interference than when the mics are switched around.
So for example, with this config:
Mic 1 (R), Mic 2 (L) > Church audio bb/pre > H120 (with 20dB gain both channels): Base Levels: -57dB (L), -60dB (R). Levels w/ interference: -36dB, -58dB
...whereas if I switch the mics around:
Mic 2 (R), Mic 1 (L): Base Levels: -58dB (L), -60dB (R). Levels w/ interference: -48dB, -40dB
The same bears out with all other combinations - ie if I apply the 20dB gain using the Church audio Pre, or replace the pre with my homemade bb, or add the AD20 after either of the bb's.
I can't figure out why this would be the case, so would appreciate any advice.
One other thing to throw into the mix, which i'm not sure is pertinent...one of the lead Rockbox developers (LinusN) has mentioned that some iriver units are not grounded correctly, though he was talking with regards to tiking introduced to recording by plugging in the remote: "...the problem is that the analog and digital ground are connected on the ticking units...most likely a mistake, since there is still a resistance.".
If you've gotten this far, thanks for reading.