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Old May 2nd, 2013, 02:11 PM   #1
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AT 875r Characteristics?

Hi All,
Id like to ask a couple of questions about my recordings of railroad locomotives. I like to catch them as they slowly struggle up hills, focusing on the locomotives themselves. I like to pan around, following the locomotives as they pass, as opposed to leaving the camera still and letting the train pass by.
I am using a Canon xf100, with either my AT875r or the internal mics.
I have read great reviews of the 875r. But in my case it seems the audio it records is dominated by a deep throbbing coming from the locos. This throbbing seems to drown out the rest of the sound somewhat, and on playback through systems with subwoofers or large speakers it spoils the whole clip ( I feel). When I record from the 875r into one channel and record from the internal mic on the other the internal seems to be a lot better balanced, although much duller than the 875r. I'm using a WindTech windmuff . The 875r is mounted on the cold shoe with a Pearstone shock mount. Im filming from around 75ft from the subject at the closest point.
Id like to ask if anyone has experienced this problem, and if anyone has a suggestion on what to do about it. If it was simply the characteristics of this particular mic then Id also like to ask if anyone knows of a mic that might be better suited. Or, if it ends up being simply the difficulties of recording large engines working hard then maybe some suggestions to counter the noise. Id be happy to add links for samples.
Scott
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Old May 2nd, 2013, 08:38 PM   #2
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Re: AT 875r Characteristics?

If that's what the steam engine actually sounds like from your shooting location, find out whether the bass sound is being amplified by something
eg: the hard ground between you and the loco. If you have a boom, raise it up vertically as high as you can, and see if you can pan it with the camera.

Then try different locations, record samples at each spot to analyse later. Number and note each sample.

Next, you'll have to reduce the bass level in the recording. The 875r doesn't have a bass cut (high pass) filter, so you'll need another mic
eg: Rode NTG-2 ..

Rode NTG-2 Battery or Phantom Powered Condenser Shotgun B&H


You might find these helpful .. Steamsounds AU

Railwaysounds pages. Steam and diesel railway sound recordings from the UK

Cheers.
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Old May 2nd, 2013, 08:49 PM   #3
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Re: AT 875r Characteristics?

Thanks Allan. It's actually diesel locomotives, the same kind you see every day on trains in the U.S. I'll go ahead and try the Rode. Thanks for the advice, I hadn't even considered the hard ground reflecting the sound.
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Old May 2nd, 2013, 08:57 PM   #4
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Re: AT 875r Characteristics?

Ah yes diesels. Me, I'd have to find out what's happening at the location first, it might be simple as moving a short distance. And record samples and keep notes. Just use your 875r first.

Cheers.
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Old May 2nd, 2013, 09:19 PM   #5
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Re: AT 875r Characteristics?

Allan, your recordings of that ALCO diesel are truly superb.I would love to get close to that. Here is what I am getting. The mic is camera mounted, and I pan to follow the locomotives.
https://www.dropbox.com/s/22xphm05qk...r%20dvinfo.wav
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Old May 2nd, 2013, 10:16 PM   #6
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Re: AT 875r Characteristics?

Thinking you could EQ a lot of that bass to a better balance, I played with it superficially in Soundbooth and got some more pleasing result.

I'm a volunteer machinist at the Gold Coast Railroad Museum here in Miami, where we run an EMD GP7 road switcher and an Alco Rs1---the predominant sound you hear on them is the 16 cylinder Diesels and, on the Alco, a 3300-pound air compressor that's driven directly by the engine, making a very loud rhythmic pulse. There's very little to them in mid-range or high frequencies, unless braking or venting air or ringing the warning bell or something.

Inside the cab, you feel the bass in your chest, it smothers everything. So what you are getting is pretty much the sound of the locomotive itself, which pretty much covers up any other sound. Perhaps you need to pick up more ambient sound---reflected sound from the area around train itself, rather than direct sound of the engine, and blend them? Maybe point a cardioid off-axis, just a thought as I haven't tried this myself......

I'm attaching a file I made with a low-cut eq in Audacity, and a screen grab of the eq curve, for what it's worth. I'm sure it can be improved, but maybe this is a step in the right direction....
Attached Thumbnails
AT 875r Characteristics?-capture.jpg  
Attached Files
File Type: wav audio for dvinfo with low cut.wav (6.49 MB, 53 views)
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Old May 2nd, 2013, 10:38 PM   #7
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Re: AT 875r Characteristics?

That's a great idea Battle and I will try that also. I will need to get a hold of a cardioid mic but that's do-able. I also think that when there are 4 or so locomotives the sounds are all interfering with each other until its a bit of a mess. Thanks for your help. I will post back with results.
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Old May 3rd, 2013, 01:39 AM   #8
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Re: AT 875r Characteristics?

The AT 875R has a built in high pass filter of around 80hz but I would agree that for machines such as a train you need to be rolling it off at more like 150-200 hz.

I suspect your camera mic may have a high pass filter inserted and hence the difference, also make sure your levels are OK and that you are not overloading the mic input or using auto gain!

I see in the manual that the XF100 has some menu LC settings (Low Cut) it may be that LC2 is more suitable for the recording with the 875R if it is available on the XLR inputs, try them and listen to what effect they have:

OFF: For recording audio under usual conditions.
LC1: For recording mainly people's voices.
LC2: For reducing the background sound of wind when recording outdoors in windy surroundings (for example, on a beach or close to buildings). Note that when you use this setting some low-frequency sounds may be suppressed along with the sound of wind.

2. Select [Audio Setup] -> [Audio Input] -> [Int. Mic Low Cut] in that order.
Push the <joystick> up/down to select the desired submenu, and then press <SET> button.

Note I am not fully conversant with the XF100 and it may be that those LC settings are only available for the internal mic but on my camera you can also select LF filters for XLR inputs.
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Old May 4th, 2013, 04:36 PM   #9
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Re: AT 875r Characteristics?

Hi Gary,
Sadly the xf100 only allows the Low Cut options on the internal mic.
Yesterday I went up and re-took some video from the same spots, taking notes and trying different options. The first thing I noticed was what Battle mentioned; that the locomotives do pound out some serious low rumble. In fact listening to them go by without focusing on what the camera was doing let me listen to the real world, and there it was; the deep rumble I was complaining about. However I did try my mic without any cover whatsoever, and it seems my windmuff contributed significantly to the problem. I don't think it emphasized the rumble. It just reduced everything else.
I still want to try a cardioid. Even if I use it for one channel and keep my 875 camera-mounted I can choose later which sounds better. So: Can anyone suggest a good cardioid which is suitable for outdoors and good for these types of recording? Thank you all for helping out. Sincerely appreciated.
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Old May 4th, 2013, 09:19 PM   #10
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Re: AT 875r Characteristics?

Unless it's an extremely still day, any mic will need protection from the breeze.

I would suggest an AT8031 (or the older version ATM-31a). It's a cardioid condenser mic that can run on phantom or AA battery. It has a moderately powerful output, so it will be less sensitive than the AT875 in loud situations but still produces a useful signal output versus a dynamic cardioid. It also has some built-in wind filtering since it's designed to be a vocal mic and the large grill can have additional furry filtering added.
It's the same body diameter as the AT875, so any of the same clips or shockmounts will fit either mic.
It also has a bass roll-off switch. They are about $170 online.
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Old May 4th, 2013, 09:40 PM   #11
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Re: AT 875r Characteristics?

Thank you Jay. I have one ordered. I will post back with results. Thanks again
Scott
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Old May 4th, 2013, 10:10 PM   #12
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Re: AT 875r Characteristics?

You're welcome! Hopefully you also caught one of the Cinco de Mayo sales, that's worth $20 off this weekend at some sites I've seen.

At any rate, I've had good results in the past with this model when used outdoors and I think it will be a more natural representation than any type of shotgun (even though I also like my AT875 and it's generally well behaved off-axis).

Also have you experimented with rotating the AT875 90-degrees around its long axis? Mics that have their openings down the sides versus all around do have a difference in response when the openings face up and down versus left and right.
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