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Old January 25th, 2011, 10:44 AM   #1
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How do I cleanly record a very quiet sound source?

I'm working on a project at the moment, which consists of a series of internal shots of a decommissioned airport terminal. So the building is totally empty and devoid of activity. However, the subjective experience of being there for any length of time reveals a multitude of sounds that aren't immediately apparent. These background noises come into the foreground: air conditioning, the buzz of fluorescent lighting, the wind outside, nearby aircraft taking off and landing, the general room tone.

I want to foreground these background noises, recording them with a clean enough signal that I can present them at quite a high volume in the final edit.

I'm a bit of a sound noob, and the only equipment I own is a Zoom H4n. I would like to ask you guys what is the best way to achieve my goal, and what equipment would I ideally need?

For example, should I consider looking for a particular type of microphone?

Do I need some way to cleanly boost the signal before it goes into the Zoom?

Many thanks in advance.
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Old January 25th, 2011, 11:24 AM   #2
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You need microphones with a very low self-noise and a good output level. Personally, I would use a recorder with very quiet mic pres. as well.

The good output level of the mics means that the mic. pre. gain can be low so you minimise noise from there.

My personal choice would probably be a pair of MKH 8020 in a Jecklin or Schneider Disk to capture the atmosphere of the place.

Alternatively an ORTF pair of MKH 8040.

An MS set of MKH 30/40 may also be OK.

I hope this helps.
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Old January 25th, 2011, 11:39 AM   #3
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you could also try to get closer to the sounds physically. Go right up to the buzzing light, or a/c unit record enough of it so you can loop it and add it in after.
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Old January 25th, 2011, 11:57 AM   #4
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John,
thanks for that info. I hadn't even considered that I would need a pair of mics for stereo sounds. Thanks for your recommendations for suggested mics. They are all out of my budget. Perhaps I will try to find a sound recordist who has similar gear and hire them to do the job.

In general, would I be correct in saying that I'm looking for a matched pair of condenser mics that have low self-noise and a good output?


Sacha,
thanks for your suggestion. I can certainly do that for the AC and lights and anything else that makes noise inside the building.
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Old January 25th, 2011, 12:57 PM   #5
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The Rode NT-1A has extremely low self noise. It also works well as a voiceover or vocal mic. It's not directional though. (Cardioid.) That's good for recording natural spaces, but not good for isolating single sources.

Getting closer to the sources and mixing in post is spot on.

Quieter recorders are nice, but expensive. The Fostex FR-2LE is great for the money. It can be modded to have quieter amps still.

Noise reduction is generally used for super quiet sounds. It needs to be used sparingly to keep from mucking up the desired signal. Music sample libraries generally employ NR when recording pianissimo notes since the source is so darn quiet.

I'd start with the H4n and try some things out. If it's still too noisy, then consider spending money on purchases and rentals. With close recording and NR, the H4n might just do the trick.
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Old January 25th, 2011, 01:43 PM   #6
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Surely the point is to record the ambience of the place? So moving in close destroys the very effect you want to achieve. As John says, decent low noise condensers and a recorder with well designed preamps are the key feature. The zooms are nice machines, but they are optimised for recording sound sources from average to loud - at the low end, you will hear them hissing gently.

Experimenting with what you have to hand is worthwhile. If you don't have to move around, you can always experiment with a pair of modest condensers and try separation and careful angling to produce a decent sound field.
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Old January 25th, 2011, 03:13 PM   #7
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Good point about making close recordings of stuff that belongs in a larger space. This approach can work, but it takes a bit of effort.

Of course, you would mix the close mic'd sound effect lower. You would also add reverb, possibly convolution reverb of a similar space to the one in your scene.

Back in the day, people would record a dry source, then play it back over nice speakers in a large space and record that. You can then mix the dry and wet sounds to taste.

Another trick was to play back the sound at high speed and record the echo at high speed as well. Playing back at normal speed preserves the pitch, but the apparent size of the space will grow. If you doubled the speed, you would double the size of the room.

One quote I love about sound design is that "we don't want the sound to be as it really is. We want the sound as we would imagine it to be." - some guy on a forum.
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Old January 26th, 2011, 11:28 AM   #8
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At a lower budget level I would suggest a pair of AT4021 cardioids (80db S/N with high output and flat response) in a traditional stereo positioning, paired with a clean preamp or small mixer and feeding an appropriate level signal into the H4n's 1/4-inch connectors.

The only way I'd try the H4n without a preamp is to test the onboard stereo mics. That wouldn't cost you anything but time to record and listen if that's satisfactory.

Also remember that airport locations can be loaded with strong sources of interference like radar and radio transmissions. Listen carefully for this with good headphones and use the best shielded cables and modern (RF resistant) mics you can.
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Old January 26th, 2011, 06:42 PM   #9
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Thanks for all the great suggestions from everybody!
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