Outdoor Soundscapes and Stereo Recording

I'm interested in techniques for capturing the ambient sounds of places and environments. This kind of recording is something of a neglected stepchild in the commercial audio world, which is overwhelmingly focused on music, film soundtracks, and similarly "professional" applications. But field recording -- documenting the sounds of the world around us -- has a long and interesting history of its own, from the late Tony Schwartz's magnetic wire recordings of New York city street life in the the 40's and 50's to the stunning natural biophonies hunted down across the world by Bernie Krause. And the Internet has brought together small but often quite vibrant communities of wonderfully fanatic nature recordists and sound hunters. But we're definitely on the margins of the audio world here, specialized nerds even by the already very geeky standards of the AV club.

We tend to take the unique sounds of places for granted, and we may not even notice when familiar soundscapes radically change or disappear out from under (or around) us. And in spite of the fact that high quality digital audio equipment is cheaper and more versatile than ever, hardly anyone thinks to use a recorder the way they might a digital camera. Ambient sound is, for most purposes, as ephemeral as it ever was. I commented last year in my blog on the strange dearth of available recordings of David Byrne's Playing the Building audio installation; Flickr is loaded with photos of the space, but hardly any visitors thought to capture what it actually sounded like. And now, like so many other sounds, it's gone.

Anyway, I've found that making good quality stereo field recordings carries its own challenges besides the obvious ones of finding interesting sounds and getting the right equipment to where they are. In particular, most research on, and commercial equipment for, stereo recording is focused (naturally enough) on serving the needs of the music industry. There the aim is to get a pleasing reproduction of a particular subject -- a musician, an orchestra, whatever -- that's located in a relatively small or at least identifiable space, usually indoors. "Ambience" in music recording has to do mainly with capturing the effect of the subject against the space. Any sounds originating from the local environment are usually considered nothing more than unwelcome noise, blemishes to be eliminated or masked from the finished product.

But the kind of field recording I'm interested in takes the opposite approach -- the environment is the subject. Most of the standard, well-studied stereo microphone configurations aren't optimized for capturing this. Instead, they're usually aiming to limit the "recording angle" to the slice where the music is coming from and to reduce the effects of everything else. There are some standard microphone arrangements that can work well for widely dispersed subjects, but most of the literature discusses them in the context of indoor music recording. It's hard to predict, without actually trying it, how a given technique can be expected to perform in a particular outdoor environment. If experience is the best teacher, it's pretty much the only one available here.

Compounding the difficulty of learning how different microphone configurations perform outdoors is the surprising paucity of controlled examples of different techniques. There are plenty of terrific nature recordings available online, but people tend to distribute only their best results, and keep to themselves the duds recorded along the way. For the listener, that's surely for the best, of course, but it means that there are lamentably few examples of the same sources recorded simultaneously with different (and documented) techniques from which to learn and compare.

And so I've slowly been experimenting with different stereo techniques and making my own simultaneous recordings in different outdoor environments. In doing this, I can see why similar examples aren't more common; making them involves hauling around more equipment, taking more notes, and spending more time in post-production than if the goal were simply to get a single best final cut. But the effort is paying off well for me, and perhaps others can benefit from my failures (and occasional successes). So I'm posting a few examples here, and will try to update this page with new recordings from time to time. Most of the clips are decidedly unspectacular, intended primarily to expose the similarities and differences of the images produced by different mic configurations when used outdoors. Mainly though, I'd like to encourage others to do the same; my individual effort is really quite pale in the grand scheme of things, limited as it is by my talent, equipment, and carrying capacity.

So far I've only processed and posted a few clips. But one of the most interesting things you might notice even from these few examples is that in some cases the differences between the clips recorded with different configurations are very subtle, only noticeable if you're listening deliberately and critically, while in others, the images are quite dramatically different. And listening on headphones will usually yield a very different psychoacoustic image than with speakers.

The clips here are all in 48KHz MP3 format unless otherwise indicated. Full resolution (generally 96KHz/24 bit) PCM BWF (.wav) versions of most of these clips can be found on www.freesound.org.

• Institute Woods Soundscape

  A small forrest, teeming with various birds and other exurban animal life, with a little running stream about 30 feet (10 meters) to the front. Airplanes, cars, and other human sounds are occasionally faintly audible, but it's a surprisingly quiet location given its proximity to encroaching suburban sprawl. Recorded 4 July 2009 at about 6pm in the Institute for Advanced Studies woods in Princeton, NJ (as pictured above). 2'08".

  • IAS_Woods_MS.mp3. "Mid-Side" stereo: a pair of Sennheiser MKH-800 multi-pattern microphones, set to wide-cardioid and figure-8, mounted with capsules nearly coincident inside a Rycote blimp windscreen (rightmost on the bracket in the photo above). Mixed to conventional L-R. Captured on a Nagra VI digital recorder.
  • IAS_Woods_Jecklin.mp3. "Jecklin disk": A factory-matched pair of Sennheiser MKH-8020 omnidirectional microphones (with Rycote "ball gag" windscreens) spaced on either side of a 30cm disk barrier (center on the bracket in the photo above). Captured on a Nagra VI digital recorder.
  • IAS_Woods_2260.mp3. "Spaced cardiod": A pair of Audio-Technica AE-5100 cardioid microphones (with Rycote "ball gags"), positioned with the capsules 22cm apart at an angle of 60 degrees (leftmost on the bracket in the photo above). Captured on a Nagra VI digital recorder with a Sound Devices MixPre preamp.

  Comment: The stereo images produced by these recordings are fairly similar to one another. The prominence of the running water to the front and the relative volume of some of the bird calls to the sides are the main variables in the images. I think the 8020 Jecklin clip is the most natural and gentle sounding of the three, although I suspect that's probably due more to the good quality omni capsules in these mics than to the imaging properties of the Jecklin disk itself, which makes the water a bit more prominent than I'd like. Note that there's very little movement of sound sources in these clips; the sound comes from all directions, but mostly everything stays put throughout the recording.

• Freight Train

  A long freight train (with a helicopter flying overhead) passing approximately 10 feet (3 meters) in front of the microphones (from left to right). The dynamic range of these clips is quite large; the train goes from the lower limits of audibility to near the 0 db point. Recorded 17 September, 2006 in Berkeley, CA. 5'34".

  • train-ms.mp3. "Mid-Side" stereo: a pair of Sennheiser MKH-800 multi-pattern microphones, set to wide-cardioid and figure-8, mounted with capsules nearly coincident inside a Rycote blimp windscreen. Mixed to conventional L-R. Captured on a Sound Devices 744T digital recorder.
  • train-jecklin.mp3. "Jecklin disk": A pair of Audio Technica AT-3032 omnidirectional microphones (with Rycote "ball gag" windscreens) spaced on either side of a 30cm disk barrier. Captured on a Sound Devices 744T digital recorder with a SD 302 preamplifier.
  • train-xy.mp3. "XY" Stereo: A Rode NT-4 stereo microphone, consisting of two near-coincident cardioid capsules at a 90 degree angle. Captured on a Marantz PMD-671 digital recorder.

  Comment: A passing train is such a cliche for stereo recording that it hardly seems worth bothering. But what I find interesting here is how the different recording techniques handle the wide amplitude range and provide different clues for when it is about to pass in front.

• San Francisco Bay

  Small, choppy waves breaking against the rocky shore of the San Francisco Bay. The microphones were positioned approximately 6 feet (2 meters) from the Bay's edge, oriented toward the water. A small airplane flying overhead becomes audible at about one minute into the recording. Recorded 1 October 2006 at Cesar Chavez Park in Berkeley, CA. 2'28".

  • water-ms.mp3. "Mid-Side" stereo: a pair of Sennheiser MKH-800 multi-pattern microphones, set to cardioid and figure-8, mounted with capsules nearly coincident inside a Rycote blimp windscreen. Mixed to conventional L-R. Captured on a Sound Devices 744T digital recorder.
  • water-jecklin.mp3. "Jecklin Disk": A pair of Audio Technica AT-3032 omnidirectional microphones (with Rycote "ball gag" windscreens) spaced on either side of a 30cm disk barrier. Captured on a Sound Devices 744T digital recorder with a SD 302 preamplifier.
  • water-sass.mp3. "SASS": Crown "SASS" quasi-binural stereo microphone, with standard electret PZM boundary capsules. Captured on a Marantz PMD-671 digital recorder.

  Comment: The images here are more different than they are similar to my ear; the only clue that they are even simultaneous recordings is the sound of the airplane. I like the image of the SASS mic best, especially on headphones, although the capsules and the recorder preamps I used for this clip have considerably higher self-noise than either of the other two clips in this example. The MKH800 MS recording has a great deal of LF rumble; you can EQ it out for a very different listening experience.