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Old 09-03-2015, 05:17 PM
Trevor B. Trevor B. is offline
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Default Weird Science.

I'm getting a strange crackling noise on specific frequencies when I record with my Gefell M300 mikes. The noise is similar to a clipping spike. It has taken me a while to figure this out but today I got the issue narrowed down to 185 Hz (F#,4th string) and even more noticeably 190Hz (G, 3rd open, or at V of the 4th string). There is less crackling but still some at the octaves both above and below these frequencies. The issue is present on different guitars, at different buffer sizes and occurs regardless of mic placement etc.. This afternoon I switched out the Gefells for a pair of AKG 451s (the old ones) and the crackling was gone. Then I set up my Sennheiser MKH 800 P48. No crackling with this mic either. For sonic clarity, presence, range etc. the Gefells are my first choice for recording acoustic guitar but the noise issue is definitely putting a damper into the recording experience. Is this an issue any one else has had to contend with and if so, what did you do to remedy the situation.

Thanks (again),
Trevor
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Old 09-03-2015, 05:24 PM
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rick-slo rick-slo is offline
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Some times it is from moisture on the mike diaphragm. Try drying the mike (A little warmth from a lightbulb - 30 minutes or so perhaps).
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Old 09-03-2015, 05:41 PM
sdelsolray sdelsolray is offline
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Quote:
Originally Posted by Trevor B. View Post
I'm getting a strange crackling noise on specific frequencies when I record with my Gefell M300 mikes. The noise is similar to a clipping spike. It has taken me a while to figure this out but today I got the issue narrowed down to 185 Hz (F#,4th string) and even more noticeably 190Hz (G, 3rd open, or at V of the 4th string). There is less crackling but still some at the octaves both above and below these frequencies. The issue is present on different guitars, at different buffer sizes and occurs regardless of mic placement etc.. This afternoon I switched out the Gefells for a pair of AKG 451s (the old ones) and the crackling was gone. Then I set up my Sennheiser MKH 800 P48. No crackling with this mic either. For sonic clarity, presence, range etc. the Gefells are my first choice for recording acoustic guitar but the noise issue is definitely putting a damper into the recording experience. Is this an issue any one else has had to contend with and if so, what did you do to remedy the situation.

Thanks (again),
Trevor
Trevor,

Was this the same strange noise I removed from your recording last week?

Derek's light bulb drying method is a good suggestion. Just place the mics in their mounts on the stands and keep them about 18" above a 60 watt bulb for some time (I've done it overnight). I don't know what you humidity is like in your studio, but if too high, or if it changes often, that can do some weird science on mic diaphragms.
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Old 09-03-2015, 06:28 PM
Trevor B. Trevor B. is offline
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Originally Posted by rick-slo View Post
Some times it is from moisture on the mike diaphragm. Try drying the mike (A little warmth from a lightbulb - 30 minutes or so perhaps).
I'll give this a shot tomorrow.


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Originally Posted by sdelsolray View Post
Trevor,
Was this the same strange noise I removed from your recording last week?
Derek's light bulb drying method is a good suggestion. Just place the mics in their mounts on the stands and keep them about 18" above a 60 watt bulb for some time (I've done it overnight). I don't know what you humidity is like in your studio, but if too high, or if it changes often, that can do some weird science on mic diaphragms.
Yes, it's the same noise. This morning I played the very excerpt you tweaked in the Seeking Recording Advise thread and recorded it again several times. The noise was there in every take. Then I record enabled the tracks but didn't record, just played into the mikes as I would to set input levels and get my headphones to a comfortable volume. The noises were still there in the same places. That's when I identified the notes (and therefore the frequencies). By inserting the channel EQ (I was recording on a single stereo track today) I was able to greatly reduce the noise every time it occurred but would rather get clean takes and use the EQ to fill out the sound rather than fix what sounds like clipping (even though my levels never got above green). I'll definitely try drying the mikes with a lamp tomorrow. My recording space is in our basement and and it gets pretty humid down here.
BTW - Despite the noise issue the Gefells really do sound much fuller and sparklier than the AKGs, although they sound pretty good too.
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Old 09-03-2015, 07:06 PM
sdelsolray sdelsolray is offline
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Originally Posted by Trevor B. View Post
I'll give this a shot tomorrow.




Yes, it's the same noise. This morning I played the very excerpt you tweaked in the Seeking Recording Advise thread and recorded it again several times. The noise was there in every take. Then I record enabled the tracks but didn't record, just played into the mikes as I would to set input levels and get my headphones to a comfortable volume. The noises were still there in the same places. That's when I identified the notes (and therefore the frequencies). By inserting the channel EQ (I was recording on a single stereo track today) I was able to greatly reduce the noise every time it occurred but would rather get clean takes and use the EQ to fill out the sound rather than fix what sounds like clipping (even though my levels never got above green). I'll definitely try drying the mikes with a lamp tomorrow. My recording space is in our basement and and it gets pretty humid down here.
BTW - Despite the noise issue the Gefells really do sound much fuller and sparklier than the AKGs, although they sound pretty good too.
My recording space changes humidity twice each year - summer (higher) and winter (lower). It varies on average from about 65% (summer) to about 40% (winter). That's not a big swing, but several of the mics I have had over the years have occasionally acted up when things change from one season to the next. My Gefell M295 mics are particularly sensitive. I started to store the mics with silica gel packets and that has pretty much solved things. Again, the light bulb trick certainly works, IF the issue is H2O condensation on the capsules. But that sound in your recordings is not like the sounds I get from damp capsules. One minor point...in your recording that I tweaked there was a second naughty noise/burp at about 10 or 12 seconds into the recording. I did not repair that one. However, it only seemed to be in one mic and not the other, whereas the first noise/burp was definitely in both mics equally.

Your observation that the noise/burp only happens at certain frequencies, with any guitar, and only with the M300 mics, leads me to think it might be a mechanical resonance quirk and not something electronic at all (i.e., neither analog or digital). On the other hand, having two mics with the same mechanical resonance issue would be very very very unlikely. Weird science indeed.
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  #6  
Old 09-04-2015, 07:48 AM
Trevor B. Trevor B. is offline
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Thanks for the input, Steve. I'm "drying" the Gefells this morning and in the meantime will call a a local mic technician who has done some repair work for me in the past. Your comment about mechanical resonance is leading me to wonder if there's some bizarre confluence of room reflections that the acoustic baffles aren't dispersing and the mikes are amplifying. Later today I'm going to rearrange my recording setup and see if that helps if drying the mikes doesn't.
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  #7  
Old 09-05-2015, 08:16 AM
Trevor B. Trevor B. is offline
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Rearranging my recording setup made no difference. Spoke to a microphone technician in my area and his advise is to try using an external phantom power supply for the Gefells. I had one but have misplaced it so it will be a few days until i know if this will be a fix.
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