Sunday, September 8, 2013

Audio-Technica BP4025 Stereo Mic - In A Field Of Its Own

Audio-Technica BP4025
You don't think about it much, but good stereo ambi - ambient sound - can add a lot to the feeling of a video sound track. But how do you capture it? There are many stereo mics and the cost range varies significantly; from several hundred to several thousand dollars. 

The Audio Technica BP4025 is a relative newcomer. B&H lists it for $649. It's a professional X/Y patterned mic and requires phantom power. It has a five-pin XLR output connector, 10 dB pad and low frequency roll-off. The BP4025 comes with a five-pin to dual three-pin XLR Y-cable that plugs into any professional mic input. 

A simple foam pop filter is included, but for serious outdoor work, you'll need something more wind resistant. The significant difference between the BP4025 and other stereo mics is that the BP4025 has relatively large diaphragms; about an inch in diameter. These larger diaphragms grab sound with less selfnoise than mics with smaller diaphragms. Selfnoise exhibits as high frequency hiss and can really spoil the sound. 
Audio-Technica BP4025 Grille Removed

My first test with the BP4025 was a simple walk around the backyard. I plugged the BP4025 into my Sound Devices 744T audio recorder grabbed my headphones and headed out. It was a great Spring day with birds tweeting everywhere. 

Using the headphones to help me find a good spot. I held the mic in my hand and hit RECORD. The BP4025 is so quiet that the selfnoise was well below the noise floor of my quiet suburban neighborhood. I heard absolutely no hiss. 

As I stood listening to nature in stereo, I spotted one of my neighbors walking her dog. She was about 150 feet away from me. As I watched her approach, I head a sharp clack. She's used to seeing me with audio gear hanging off me and as she got closer, she stopped to see what I was up to...THIS TIME. 

When she got within comfortable conversation range I noticed she was chewing gum. I asked her if she had clacked her gum as she was walking. Yup. That was the clack I had heard from about 150 feet away. 

The recording proved very useful a few months later when I was posting "Hot Flash", a double award-winning indie short I produced last year. There was a backyard scene in which Diana Sowle, wearing an electric dog collar, walks aimlessly across the lawn, only to be stopped by an invisible electric pet fence. The boom mic was obviously not in stereo, nor did it hear much ambience. It was not a nice Spring morning and there were no birds chirping. In fact, there was a rather noisy air conditioner across the street.

"Comes With" Accessories
The stereo ambi track fit perfectly. I chose a particular section so the scene opens with a particularly nice bird tweet. No one has ever questioned me about the sound. No one knows, until now, that the ambi was from a different neighborhood on a different day. 

You can hear for yourself at the HotFlashMovie web site. I've always felt the most important quality of great sound is that is doesn't draw attention to itself. Since then I have continued to record stereo ambi and have created a small but growing archive of great sounding stereo ambi tracks; all done with the AudioTechnica BP4025.

If you can't afford the BP4025, there's always the lesser AT8022.

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