level ok, but sound distorted
 

Hi,


I ran into this problem recording audio.
I'm mostly recording hand-drums.
I use 1 lavalier mic which goes through a channel strip into my Sony EX-1, and one Neumann km184 that goes directly into the camera. The Neumann is standing behind the drum. Those drums are nut super loud, but bassy.
Although the levels are far from red, the bass sound gets distorted in the recording, mostly from the mic behind the drum.
I usually think as long as the level is ok, the sound is gonna be ok, but apparently that's not always the case.
Any idea why this happens and how to prevent it?


thanks,

David

The Drum could be overloading the mic element even though you are recording the level within limits. Try moving it farther from the source or point it slightly away from the sound. Low frequencies can also be easily over recorded as the meters don't always reflect the spectrum equally. The more sensitive the mic the more likely it will overload on loud or strong frequency sources. A dynamic mic can probably handle the drum sound in very close proximity while the Nuemann might sound better from farther away. HTH

If your camera level indicators are like mine (Canon XHa1) , they read the output from your preamps. So the input level can be overloading the preamps and maxing out your waveform, and even if you turn down the camera audio level, you're just making a lower level output of a distorted waveform....your channel strip, if it has a level meter, should intercept that, but the mike going direct into the camera may be maxing out. If you have mike attenuation on your camera, try that and see if it helps...also, brief transients (drum hits) don't meter accurately at best as the meters take time to respond..../Battle Vaughan/miamiherald.com video team

Mics have a rated SPL limit on them. Most SDCs like the Km184 can't handle too high of SPLs (I don't know the specific model, but check it), and they will distort if too close to a loud sound. A dynamic mic is great choice for this as they have great SPL handling.

David, hello from a fellow framedrummer - I've seen your youtube videos and visited the new website. Great work!

Distortion can occur at various stages, for example, your mixer preamp can overload, then, that distorted signal can be lowered... but of course it still sounds bad. Or, as pointed out, even the diaphram of a small condensor can be overloaded.

The solution is to monitor and adjust at each stage - a good pair of headphones to help with mic positioning and volume adjustments will really shorten the cycles of trial-and-error. If you're hearing distortion you'll need to look at every stage where volume can be adjusted.

Also, be aware that auto-gain may work *very* poorly for percussion instruments - manual is best. Meters may understate the peaks by quite a bit with percussion, so peaking the camcorder meters at no more than about -20db is a good start.

Finally, microphone positioning is pretty critical for close-micing frame drum. Mostly I mic in front of the rim, perhaps a little bit in from the rim, at a distance of perhaps 15cm. Micing towards the center can get very boomy.

I've used a Shure Beta57 quite a bit on stage as well as recording, it's done well when positioned to the rim as above. (this is a very different mic than the SM57). Occasionally, I've recorded with a small diaphram condensor similar to the KM184, best results at about 30cm.

thanks for all your replies.
Seth, that's a nice surprice, who says frame drumming is such a niche thing...:)
When recording video, I have the Neumann behind the drum, for image reasons. With a bit af sound tweaking the sound is really good as long as the original signal is not distorted. I moved the mic further away which took care of the problem 99%.
I could also go through a pre-amp and then into the camera with line levels, as far as I understand that might also solve the issue, right?

by the way, if it's not the mic itself, would the mic gain setting in the menu affect this?

David, moving the mic away will help but it might change the quality of your recording.

I would keep the mic placement close and try two things:

1) look in your camera's audio menu and see if there is a mic attenuation setting. This will look like -40, -50 or -60. This setting will have the most impact on the signal is it goes to the pream in the camera. -40 giving the most protection fpr high SPL.

2) look on your mic and see if it has a switch to change the SPL. This will look like 0, -10, -20. This will limit how the mic responds to high SPL.

If you do not have either 1 or 2, then change mics as this mic is not suited for this task.

Good luck

That's SPL handling. I am quite positive about that (unless you were clipping, which you should know to avoid...)

SPL = ?

Could someone define this bit of jargon please. It sounds the level that the mic can handle before it distorts?

Safe playing level?

Sound Pressure Level

Sound pressure - Wikipedia, the free encyclopedia

OP:

The KM-184 is a pretty high output mic. It can put out +10 dbu (6 db hotter than LINE level). It can handle 138 SPL levels (permanent hearing loss: 120 db, threshold of pain: 130 db)

Doubtful you are overloading the mic.

What you are overloading is Sony's not so well designed preamp.

I would try, in order:

1. If the Sony actually has a preamp gain control (in a menu, as mentioned above), reduce it as much as possible.

2. If that doesn't work, use an inline pad.

3. Back off the mic. I also agree with Seth about the mic placemnt - you will get better definition on these drums with more of an edge placement. And 'enough low end' is usually not a problem - plus it's easier to add a little low end later than to fix distortion...

You would be far better off using an external mixer or preamp for this sort of thing.

Unfortunately the KM-184 has neither a built in pad nor low cut filter. The older KM-84's have a 10 db pad which I always use when close micing drums.

It is quite likely what is causing the overload is subsonic, so an external low cut filter could fix the problem with no audible effect.

Recording Drum Audio
 

Last year I recorded various Native Americans drumming and singing at an outdoor powwow celebration. My set up was a Rycote zepplin covering a Sennheiser shotgun attached to 3 channel mixer and linked to a digital audio recorder.

My audio input was peaking as the drummers hit the drums and I had to adjust my mixer level so I could avoid "Clipping". After running some tests and making final level adjustments I was set to record.

You must be able to monitor the audio and adjust the levels. For loud sounds Shotgun mics for me worked allot better than lavalieres that have to be closer to the sound source.

Maybe, but if you are overloading the preamp it should be obvious because you should read that it is clipping. If you need a pad, this guy sells inline attenuators cheap and he's a really great one-man show:

Naiant Studio Store - Clever Devices

Just get a -12 db if that's what you need, though he has all sorts of models.



Though I don't think you need an external pad... you said you were using a channel strip already. Almost every channel strip I've dealt with has a pad and a low cut. Just engage them and see what happens

I use 1 lavalier mic which goes through a channel strip into my Sony EX-1, and one Neumann km184 that goes directly into the camera.

Channel strip was used on the lav only. He might have better luck with that reversed, feed the less peaky lav direct into the camera and use the channel strip for the difficult drum.

Something else I remember about Sony cameras is that the level indicators on some just do not show fast peaks well.