Posted by: recordingsofnature | July 4, 2016

Acoustics of Nature recordings

In continuation of the post on Road noise and weather factors, I’d like to share a few more  thoughts and views on the topic of outdoor acoustics in audio field recordings, and attempt to give my guidelines on factors to consider when recording in the field. E.g. in terms of choosing the exact location of the microphones and planning with respect to weather etc.

05_IMG_6796_gron lovskov

The dense canopy of a beech forest in summer will often create hall-like reverberation

In all, I think this is a very interesting topic which I am really just slowly starting to get a grasp of. There is no right or wrong recordings. When opening your ears to these acoustic effects it opens another dimension when listening to field recordings, like an ability to sense the surroundings, the environment and weather in a new way.

Acoustics conditions of nature recordings

In my view, all outdoor sounds are deeply controlled by a variety of different acoustic conditions. It may not be very noticeable out in the field, as everything there just sound normal as always. It is only when listening to the captured sounds at home, in living room conditions, it becomes surprisingly (and frustratingly) clear how much the whole soundscape is formed by the local acoustics of the surroundings.

In the same time, it is also clear that nature sounds; birds, animals, rustling leaves, rain, insects, streams, etc. need interaction with their natural environment in order to sound natural and to be complete. It could be gull cries echoing between cliffs, the little wren’s powerful voice from the forest bed, or rain falling on the leaves or ground. Sometimes the surroundings act almost as an instrument or resonance chamber which give the voices their fullness, depth and other well-known characteristics.

So, these are some of the fundamental conditions of field recordings. In order to start to get hold of the these acoustic factors, I think the most important factors to consider are:

  1. Local acoustics conditions, look for sound reflecting and absorbing elements
  2. Wind conditions

1. Local acoustics of a place

It is clear that some places, for some reason, have more appealing acoustics than others. Those are typical places with a natural pronounced reverberation, ie. where all sounds are supplemented by the reflections of the surroundings, and thereby getting depth and perspective into the stereo image.

Other locations may completely lack these reflections and here the sounds can be much drier and attenuate faster over distance, almost comparable to an anechoic chamber.

To evaluate the acoustics of a location it is a matter of looking out for sound absorbing, sound reflecting or transparent elements in the surroundings.

  • Open land produces few sound reflections – the sky is one big absorber. Recordings here, will typically be very clean and dry, with rapid attenuation over distance. The wind direction is extra important to consider here.
  • High grass, low vegetation and bushes are normally also highly absorbing and will tend to damp the sounds and their reflections. Bushes with dense and thick/wet leafs may start to have more sound reflecting properties.
  • Taller trees, tree groups or woodland edges will normally start to produce sound reflections. Mountain walls, cliffs, buildings etc. are of course even better
  • Being inside/under tree or bush vegetation will create a local room with special acoustic conditions. It may also shield the outside sounds.
  • Forests can have very special acoustics. Especially tall beech forests, in summer can produce an almost hall-like reverberation. I believe this is mainly caused by the canopy where all leaves are competing to capture the light, therefore forming an effectively reflecting ceiling.  The acoustics will vary with the tree species; pine woods seems to be much duller and absorbing.
  • The acoustics of a  location will change through the seasons, especially with regards to leaves and vegetation. In winter, when it is mainly bare tree trunks and branches the acoustic conditions becomes rather transparent and open often with few reflections.
  • In general it is beneficial to have a direct line of sight to the sound sources that are most important. Good viewpoints may therefore often be places where you hear sounds well.

2. Wind

Wind is a very important factor for outdoor recording – more important than the other ‘invisible’ weather factors relating to temperature and humidity. Stronger winds are usually very disturbing for field recordings, but even for lighter winds, there are many aspects to consider. The wind is especially important for sounds that travel over longer distances. The wind always tends to bend and guide the sound in the direction of the wind, and even for light winds, the prevailing wind direction will strongly amplify sounds upwind and dampen sounds downwind.
  • In many cases I think it is good to have the wind coming from the front, as most sounds automatically will come from this direction. It gives symmetry in the stereo image.  It also helps to capture distant sounds in front of the microphones.
  • Upwind conditions will also help to capture delicate reflected sounds and reverberations, which are sounds that travels over longer distances. Hereby improve the sense the room and depth in the recording. Wind from behind will typically reduce these reverberations and result in a more dry sound.
  • The wind direction is also important regarding far distance background noise, especially road noise. An unfortunate wind direction can easily bring noise from distant motorways, while on the other hand, a favourable direction can be used to shield the noise from more a nearby one.
  • Calm weather gives the best opportunity to capture the special acoustics of a place, free of any wind rustling noise or other disturbances in the stereo perspective. This is when one can really start to notice faint sounds and sense delicate echoes from all around.

Reference sounds, fix points

I final point I believe will help the listener to better understand the different acoustic conditions is to include reference sounds or fix points in the field recording. This could be any familiar sound with a familiar sound volume, such as the sound of footsteps, talking, or even an aircraft passing the sky. Apart from helping the listener to adjust the sound volume to a natural level, this will also help to relate to the acoustics and give sense distances and perspective.

The above list of guidelines is just an attempt to compile my own experiences and views on how acoustics influence outdoor recordings. In that way there could easily be areas where I have misunderstood some things. Feel free to comment and share your views and experiences.
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Responses

  1. Well done – a good summary!

    Just one point, the pine forest; I find they tend to amplify and clarify sounds; hard to describe, it has its own signature, more like being in an empty room or under a brick arch with a very short reverberation. The human voice travels well in a coniferous forest. As with all forms of acoustics, our observations and perceptions will vary depending upon the frequency of the source and the sensitivity and selectivity of our receivers (hearing!).

    I enjoy listening to your recordings, although I sometimes have to limit my time listening to them, especially the long duration ones 🙂

    Like

    • Thank you for the feedback and details on the frequency element of det forest acoustics, -and learning new words (coniferous) 🙂

      Like

  2. Interesting observations about the deciduous and coniferous forest acoustics. The make up of the two types of tree are so different that it inevitably produces a notably different sound environment. We have a forest near us which switches from the one type to the other in different areas and the sound of the wind as it sweeps through the broad leaved trees and then the pine needles of the confers is fascinating. Aside from the differences produced in different seasons, the broad leaved trees produce a higher pitch of sound with more reflection whereas the conifers and their needles have a more dampening or muffling effect which considering their construction, is exactly what you would expect.
    One thing is for sure (it seems to me) is that the moment I hit the record button an airplane will fly overhead!

    Liked by 1 person


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