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Gear / Technical Help => Microphones & Setup => Topic started by: greenmtnsrider on September 07, 2016, 11:10:41 PM
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I've had my 414 XLII's for a couple weeks. Ran them outdoors in hyper and all ran fine. Great sound. Ran them indoors onstage for an acoustic gig in omni and I noticed my pre (fp24) was flashing red. No clipping transferred over to my recording but I basically had to pad the mics down to -6 and run the pre just a tad over the lowest level. Any help would be great. Thanks!
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Which LED was flashing red? Was it the one over on the right by the headphone socket, or one or both of the ones over on the left, above the gain knobs? If it was over on the right, don't worry unless you're listening over headphones (risk of hearing loss).
Your microphones, with their 23 mV/Pa sensitivity, could definitely drive a Shure FP24 (a/k/a Sound Devices MixPre) into clipping--though if I've done my calculations correctly, the SPL at the microphone would have to be ca. 121 dB, which is very loud. Still, at close range in front of certain instruments, amplifiers or voices, that's entirely possible. I've recorded opera singers who reached about 122-123 dB SPL at about a 1-foot miking distance, and if you go even closer, the SPL rises rapidly.
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Both of the LEDs above the gain knobs. I wasn't extremely close, but close enough. I'd say probably between 2-3ft away from the guitar at about abdomen height where the guitar would sit if one was standing up. There is a single monitor underneath, but I've never had a problem with that before.
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Hmm. Did you hear any low-frequency disturbance in the recording, like air currents from room air conditioning? (At this point I'm just guessing along with you.)
BTW, you probably know this, but the LEDs go red when there's still about 3 dB of headroom left in the circuitry. So if they only flicker occasionally, any actual clipping is pretty unlikely.
The Sound Devices preamps, which are admirable in so many ways, are designed mainly for film and video sound--basically dialog and effects recording. The input transformers step up the incoming signal voltages, and the preamp circuit has more gain than would be ideal for high-output condenser microphones on program material that is loud continuously; later models pad the inputs even further (15 or 20 dB instead of 10) when the powering for condenser microphones is switched on. Plus your particular microphones, at 23 mV/Pa, put out about twice the voltage that the majority of studio condenser microphones put out for a given SPL. So this combination of equipment is somewhat prone to this type of concern from time to time.
You might want to carry a pair of in-line resistive pads in your kit bag, and have them ready to plug in at the inputs of your FP24. They don't interfere with phantom powering and unlike the pad switch on the microphones, they don't inherently compromise the signal-to-noise ratio of the recording.
--best regards
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fp24/MixPre inputs are HOT.
I think it's common with many mikes (depending how hot the mikes are) that the gain knobs NEED to be nearly turned all the way down... and if I remember correctly, I think that they can be turned all the way down and still pass a signal. It's been a long time since I've ran one, so I might be incorrect on that though.
Great pre amp, but yeah... be prepared with some sort of attenuation pads if needed.
As noted above, it probably had to due with the low end frequencies.. the omni setting will give you more "thump" than the hyper setting.