AF100 crackling audio when recording high volumes

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Phil1076

Well-known member
So I shot a wedding a few weeks ago (my first with the AF100) and they had a live band playing very loud. It was a lot of fun but when the drum hits hard, the AF100 inserts static into the track. All my levels were were low...nothing was peaking into the red....at one point I even turned the gains all the way down....every time the drum hits, there is a crackle/static.

Is there a way to get this fixed? I know there is another person on here who had this issue but I can't find the thread.
 
What mic? Microphones are capable at certain levels and maybe you exceeded the maximum spl for that mic. For instance, the Audix SCX1/HC has a maximum spl of 130dB, which is why it's used as drum set mic. It's also a pretty good Hyper cardioid dialog mic. Just speculation, mind
 
Exactly. Some mics are made to handle really loud noise levels (spl = sound pressure levels) but aren't very good at low sound levels, some mics are great at low sound levels but will overload in high spl environments.
 
Steve Kahn said:
Yep. You need a mic pad for virtually every mic out there to play well with the AF100
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A mic pad won't help if you're dealing with a low-sound-pressure-level mic in a high-sound-pressure-level environment. It's the mic itself that's distorting the sound, not the camera. If the mic is too sensitive and it's getting hit with massive sound waves, it'll distort. Doesn't matter if it's plugged into an AF100 or a SD744T, the mic itself will distort the sound because its tiny pressure-sensitive elements are getting blown around by those super-high sound pressure levels.

The solution is to use the right mic for the job. There's a reason people use dynamic mics to record explosions and gunshots instead of using a super-sensitive condenser mic.
 
It depends on where the pad is applied. If the pad is applied after the microphone circuitry, it will do basically nothing
to keep the microphone from saturating. However, if the condenser mic provides a pad/bias switch ( usually -20db or more), then
the plate bias is adjusted down to reduce the microphones sensitivity. It won't hear the quiet things as well .. but it will be
much more difficult to saturate at higher SPL's.

Everybody's right that dynamic mics tend to handle high SPL's better than condensers .. and it's a pure matter of physics. Dynamic
mics move a coil of wire over a magnet as an inductive transducer. When that coil of wires travels as far as it can, it can no longer
induce any more current into the mic. A condenser, on the other hand will continue to pass current as long as the two plates
are very near one another. So, the effect of saturating a condenser mic results in a much harsher and noticeable "white noisy"
type sound.

So if you know you have a large dynamic range .. reach for a dynamic mic. Or switch mics .. condenser for ceremony, dynamic for party.

As to whether it can be fixed, there are some audio tools (like iZotope's RX) that I use to repair clips and saturation. While it can't completely
repair the clipped transient, it uses some fancy algorithms to approximate what it thinks should be there. The results are never perfect .. but
it can make an unusable audio track tolerable. Shoot me a PM if you want me to try and fix it up for you.

jeff
 
I had what sounds like the same issue while using my Sennheiser ME66. Mine was making strange, electronic sounding chirping noises at very low input levels. I noticed the noise both while recording a rock concert as well as in high wind situations. Turinig off the Automatic Limiter Control (mic ALC) in the recordings menu stopped the issue completely.
 
I had a few audio recorders going and I'm not talking about distortion here, it's a crackle -- like an electro-static crackle. The source in question here is the on-board mic of the AF100. If I turned the gains all the way down to zero (so that volume levels weren't even moving), it still crackles.
 
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I also wanted to mention that I had an HMC150 as a B-cam and the audio from that is perfectly fine. I have one channel using the internal mic and a R0DE NTG-2 on the second channel....both fine.
 
Phil1076 said:
The source in question here is the on-board mic of the AF100.
Click to expand...

I'm going to channel the late/great Henny Youngman on this one ..

My recommendation is to forget that there's an on-board mic on the AF100. It is not suitable
for anything beyond YouTube quality audio.

I never use the AF100 Mic-Pre's either. I use external MicPres (preferably) or an external field
recorder (most preferable).

jeff
 
Phil1076 said:
The source in question here is the on-board mic of the AF100. If I turned the gains all the way down to zero (so that volume levels weren't even moving), it still crackles.
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Yes -- because the mic itself is being overloaded. You can't use that onboard mic in such a high sound-pressure-level environment.
 
Phil1076 said:
I also wanted to mention that I had an HMC150 as a B-cam and the audio from that is perfectly fine.
Click to expand...
See, that's almost funny because when the HMC150 came out we had a thread exactly like this, of people recording live rock bands and complaining that the mic on the HMC150 was crackling, whereas the one on their DVX100B was perfectly fine...
 
Any way you look at it and any way you try to explain it, if it wasn't for the audio from the HMC then I'd be screwed. This was a live band in a run and gun situation...no time for preamps or anything like that. It wasn't about the quality of the audio -- it was about just capturing the audio as the band members walked amongst the crowd and played their instruments.

When a mic is overloaded the audio distorts...this is normal. I've never heard of a mic introducing extremely high pitched static; at least not in a $4000+ camera.

I guess it's just another limitation of the AF100 to work around...

On a separate note I will say, though, that the image quality and low light performance of the AF100 with the Oly 14-35 was amazing.
 
I think it is really dependent on the microphone used and the situation in question. In a previous life I used to record concerts and it really depended on where we were that dictated which microphones we used. Were they transformer mics or tranformerless, very sensitive or not so sensitive. Logging another "limitation" of the AF100 is very frustrating to me as the AF100 is no more limited than any of its competitors in a similar scenario. However when it is logged as a limitation, here on the internet, it will be here long after you have sold your AF100. And others will read this thinking that it must be true and thus will shy away from using it because it has this "limitaion." Gentlefolks, the point is that you need to understand how the microphone works, what its output level is, make sure that it is matched to the input and then setting input levels that optimize performance. Failure to do so will get you blech! And this is true whether you are using a 7" reel to reel running at 30 ips or a camcorder.

I have had a radio station come in on a recording because we used the wrong mics for the location, transformer mics instead of transformerless. Don't blame the camera for the lack of fully understanding the system. Learn the dynamics of the system and where the system will fall down. Yes, all that info is in the little spec sheet that comes with the mic. If you are going into an environment that will test the upper limits of the SPL of a given mic, get a different mic. A pad is not going to be of much value, the capsule will be overloaded and the pad will just make it a lower volume distorted audio. Knowledge is power and will always get you the call-back.

Thanks,

Jan
 
Like I said...I'm glad the HMC's mic has a supersonic transformerless flux capacitor rectifier and was not overloaded, as it saved me.
 
I'm using multiple mic's, two (lav-> radio) into a Tascam field recorder and a couple of shotguns into the camera (sometimes one and camera mic in other channel). I always figure I can throw away extra tracks. So to show my ignorance on the AF100, is there any reason to run the ALC beyond crazy out of the blue loud disturbances? This isn't really a run and gun camera, and handheld I still have a short shotgun mounted. What's the consensus on the camera's ALC? Is it full level control (including auto-gain) or a limiter type control. The manual doesn't make this clear to me.

EDIT:
Whoops- the ALC question is answered clearly and concisely in this thread:

http://www.dvxuser.com/V6/showthread.php?277645-Audio-Limiter-within-the-AG-AF100

Sorry
 
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Barry_Green said:
See, that's almost funny because when the HMC150 came out we had a thread exactly like this, of people recording live rock bands and complaining that the mic on the HMC150 was crackling, whereas the one on their DVX100B was perfectly fine...
Click to expand...

My DVX-100 and HVX-200 handled concert sound fine. My HVX-200a however cracked and popped like a mother.
 
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