Multi microphone setup feedback issue baked into recording

[James35188254icgi]

Hello, 

I did my first oral history interview using 3 microphones run through a Mackie mixer output to a Zoom H5 recorder. I used two SM-58 and a SENNHEISER MKE 600 SHOTGUN using the phantom power switch of the mixer. I will say that I am not a professional sound engineer but have had some experience in the past. I tested all the gear out ahead of time as well but did not expect to get feedback. I am also just learning Audition. My hunch is that the feedback might have been caused by the reflective surfaces but that is all it is at this point. No speakers were setup so that can be ruled out as culprit. 

The interviewee was captured on the left channel (Sennheiser) and the two interviewers (SM-58s) were captured on the right channel. We recorded it in a library with no sound dampening. The microphones were set on a wood table with their windscreens. I set the gain on the Zoom recorder to 8 to achieve about a -12 db level. The output of the mixer was set to 0 and the microphones at near 0. The feedback crept in a three occasions. I have tried to determine which microphone was feeding back but haven't been able to. I did mute one of the SM-58's when the person wasn't asking questions. 

I have listened back through the recordings and used the Spectral frequency display to identify where the feedback occurs. I'm afraid the feedback might be baked into the recording and I will not be able to either remove or lessen the impact. It happens during questions being asked. 

Questions for the group: 

Has anyone experienced something like this?

Is there a work around to reduce/eliminate the feedback in Audition? 

Advice on work arounds for future recordings?

Many thanks, 
Jim DaMico 

[emmrecs]

Is this really Feedback, which creates a "howling" sound, ir is it actually Crosstalk where one (more distant) mic picks up the same audio as another (intended to pick up the person speaking), often with a delay so causing an "echo" effect?

[SteveG_AudioMasters_]

We could perhaps be a little more specific about this if you could provide us with a sample of the results...

[James35188254icgi]

Thanks everyone! It sounds more like a howling than echo.

SteveG, I made clips of  the first "Feedback" on both channels.

These were the settings on the Mackie (phantom power on, levels set to Unity)

Mic 1: Pan Left, Gain = -20db, Low cut filter on

Mic 2: Pan Right, Gain = 30

Mic 3: Pan Right, Mic Gain = 30 

Main mix = Unity

The interviewee is isolated on channel 01 and the interviewers are on the channel 02. I did keep the microphones open throughout to ensure I captured the dialogue between the three people. 

I hope this information and clips helps to troubleshoot this issue. 

Many thanks, 

Jim

[SteveG_AudioMasters_]

How were you monitoring this recording? There's definitely something that sounds like feedback there, certainly, but it sounds very local to the mic. You weren't by any chance using a headset, were you?

[James35188254icgi]

Hi Steve, I was using standard headphones. What I think happened is a combination of a few things with the context that even though I tested the setup on multiple occasions, I am still in the learning stages of using the above combination:

• The gain was too hot on the all the microphones. 
• I used the phantom power on the mixing board instead of opearting off a battery
• The shotgun mic stand was bumped or a loud throat clearing may have caused the feedback
• The interviewee did occassionaly hit the table while making a point

Not being an audio engineer, I am not entirely sure how these factor into causing feedback. I did another run through with the board and microphones and now have standard recording levels to use and a better understanding of the controls. Going forward, I plan to add additional boom microphone stands and eliminate the table. 

Thanks to everyone for sharing their knowledge. 

Jim

[SteveG_AudioMasters_]

If you have a mic with the gain turned up near a 'normal' pair of headphones, then even if they are fully on your ears you can have a feedback path from the mic through the rear of them - quite easily! The last two points in your list wouldn't cause feedback, they'd just make clonking noises. Phantom power from the board wouldn't affect this in the slightest.

[James35188254icgi]

Thanks Steve! Very helpful.