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Old May 31st, 2004, 12:39 PM   #1
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A-T 835ST - When to use the roll off?

OK, this is a sample of 1, but I think I have found the best time to use the low-frequency roll-off switch on my mic. I have been having a problem I have been trying to figure out. When I am recording a drum corps, I will have my 835-ST on a mic stand with a 25' 5-pin cable into my A-T supplied 5 to 2-3pin XLR into my DXA-8 Beachtec. The mini-jack is into my Sony VX2100. I check and recheck my levels to the pit, drumline, and Doctor Beat (the pit is all of the non-marching percussion including 'bells'). I have the audio on manual at 20-25% on camera. Limiters are on. I do not get any redline indication in the on camera audio levels. New, fresh battery.

The moment the high brass, aka trumpets, start to wail, I pickup a slight crackle. It was baffling. I thought I had a static ground out. I tape the connectors even.

As a last resort last night (after I had already shot what I really wanted to record), I tried the roll off switch to on (a 'bent' line). It seems to have disappeared.

Was I just lucky in this one instance or could the roll-off switch be the fix? I thought it being low-freq roll-off, it would be something like the bass drums (and however you spell timbani, err kettle drums) that would affect it. What am I missing?
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Old June 1st, 2004, 10:23 AM   #2
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Your DXA-8 may be overloading the input on the camera due to the total energy of the loud passages, including extra bass energy. This can occur before the level controls and metering, so it would only be noticeable while listening to the loud passages and it may be most easily noticeable in the high end.
Engaging the bass roll-off is probably robbing enough energy from the signal to eliminate this overload. It's also possible that this low-end energy isn't even audible on your camera, so you may be able to get away with it with no ill effect on your audio.
You'll have to do some further experimentation with the DXA-8 levels, the limiters if they are adjustable, etc. to find the best combination.
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Old June 1st, 2004, 05:17 PM   #3
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Thanks Jay. It might be. I think I am safely inside the range of the mic.

I will leave the roll-off on for awhile and see if that has cleared it up.
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Old June 1st, 2004, 05:43 PM   #4
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Sub sonic frequencies and extreme lows can overload a microphone very easily. There is also a paragraph that addresses this issue in the PDF from Audio - Technica. This could also be the reason they included the bass roll off. An outdoor drum corps is a difficult subject at the best of times.

http://www.audio-technica.com/prodpro/addinfo/AT835ST_english.pdf
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Old June 4th, 2004, 11:19 AM   #5
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I am in post now and I think I may have found the contributing factor, wind. It was breezy. I has a Mike's Muff on, but the gusts were probably over 10mph but closer to 15. So, the wind noise may have help.
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Old July 11th, 2004, 01:03 PM   #6
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A post-mortum. I think I have isolated this to the mic. The field is just too loud for it. If I am about 20-50ft away, the elements in the mic are the culprit. I found this out when my battery was low in my DXA-8 this weekend at Portland Head Lighthouse. I got the clicking static when I moved the camera. The Beachtec was not rejecting the noise and had low phantom voltage because of the almost dead battery. I could tap the mic gently to reproduce it. Pulled the Mike's Muff and foam cover off (man, do they reject noise!) and could physically see the elements rattling in time with the noise.

I guess my best bet is to figure out a way to dampen the volume to the mic to reduce its sensitivity. Otherwise, I need to make sure my mic has a little more distance from the source. In the event environment, it may be best to figure out how to dampen the input.
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Old July 11th, 2004, 03:13 PM   #7
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Buy an in line pad (attenuator)
AT adjustable pad

UniMute

B&H cheapy

For the two AT products browse the same section of B&H as the link takes you.
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Old July 11th, 2004, 03:17 PM   #8
 
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Stick in a -50dB attenuator, that should clear you up. Not expensive at all.

[edit] oops, Bryan was posting the same thing/same time. Great minds and all that...:-)
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Old July 12th, 2004, 12:23 PM   #9
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DSE, -50? I did not see such a critter at B&H. Do you think I should pursue it?

Thanks guys. Otherwise, I will try the A-T solution. I will need two and I think the A-T may be the best bet with the selectable -10/-20/-30.
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Old July 12th, 2004, 05:19 PM   #10
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Bring on the corps...

Just a slight mid-stream adjustment. I found Shure 50dB attenuators locally. So I will play with them tonight and try them Thursday. I will let you know.
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Old July 12th, 2004, 06:27 PM   #11
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No joy. With the 50dB attenuators inline, I get 0 audio. Full gain everywhere and 0 noise except a camera hiss.
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Old July 13th, 2004, 10:51 AM   #12
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Ok, Update... lost count.

The attenuators are back at the store. Beachtek responded too. I do not know a way of using them now. Harry at Beachtek said that 20dB would be about right, but I lose my phantom voltage through the pad. Bad, as the 835st does not have a battery. Those A-T pads support phantom, so I guess I will order 2 and try it. But he also says I may want to switch to a dynamic mic as I may just be too sensitive ;) .
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Old July 13th, 2004, 11:35 AM   #13
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Yes, 50db is way too much. The AT -10,-20,-30 switchable pads will support phantom power and are very useful to have on hand for a variety of situations. I'd order a pair to test out at -10.
However, if the mic elements themselves are being totally overdriven, then these attenuators won't help. The distortion will be occuring before the attenuation.
If the distortion is occuring downstream from the mic, then the attenuators may help. It will depend on exactly where and how the distortion is occuring.
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Old July 13th, 2004, 12:00 PM   #14
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Thanks Jay. If they arrive in time, I might be able to get some time before Spirit performs to do a level check. Usually, the groups before the top 12 corps are just not as loud, so it is always a guess until the blast comes. I may take a dish towel and hang it over the mic while on the mic stand and see if that helps as a last resort. The budget just does not include getting a new set of mics yet. I have to buy some other hardware for field reproduction first. sigh.
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Old July 14th, 2004, 09:38 PM   #15
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Got the AT8202s today. They work. Live fire test tomorrow night.
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