The soundscape, as defined in Wikipedia, is a sound (or combination of sounds) that forms or arises from an immersive environment (http://en.wikipedia.org/wiki/Soundscape). Some dimensions of the soundscape can be quantified, and others cannot. In Chapters 2 and 3, U.S. activities related to noise in quiet areas is described. This appendix describes two international efforts to describe preferences and tranquility in quiet areas.

A recent study was done in Hong Kong of human preferences in countryside soundscapes. Based on questionnaires, interviews, and recordings taken during interviews (Lam et al., 2008), there was a clear preference for countryside sound sources; natural sounds were preferable to man-made sounds. The order of preference was found to be:

• running water

• bird

• wave

• waterfall

• wind

• insect

• other animals

• human

• road traffic

Aircraft noise is not listed, perhaps because the Hong Kong airport is on Lantau Island, not Hong Kong Island.

The sound recordings were also analyzed according to A-weighted levels and sound quality metrics, but no strong correlation between preference and acoustical quantities was found. This does not mean that acoustical quantities are unimportant; it may mean that the appropriate metric for these quantities has not been found. The authors conclude:

In the United Kingdom, the Campaign to Protect Rural England (CPRE) has done extensive work related to tranquility (CPRE, 1995). Tranquility—partly the landscape, partly the soundscape, and partly human experience—is a difficult concept to express in numerical terms. Nevertheless, the CPRE has developed a method based on the results of questionnaires and the identification of factors that contribute to tranquility. Although the algorithm used to determine the numerical value is not given on the Internet site, an attempt was made to assign a tranquility value for every 500 X 500 meter area of England. Maps are given on the Internet site, and sounds may be downloaded.

Based on surveys, the Internet site defines the 10 top factors that contribute and do not contribute to tranquility:

What tranquility is:

1. Seeing a natural landscape

2. Hearing a bird sing

3. Having peace and quiet

4. Seeing natural-looking woodland

5. Seeing the stars at night

6. Seeing streams

7. Seeing the sea

8. Hearing natural sounds

9. Hearing wildlife

10. Hearing running water

What tranquility is not:

1. Hearing constant noise from cars, lorries, and/or motorbikes

2. Seeing lots of people

3. Seeing urban development

4. Seeing overhead light pollution

5. Hearing lots of people

6. Seeing low-flying aircraft

7. Hearing low-flying aircraft

8. Seeing power lines

9. Seeing towns and cities

10. Seeing roads

A physical description of the soundscape is one input to the assessment of the human experience, even though it may be described as an overall good experience, as a preference, or as a tranquil environment. One has to distinguish clearly between man-made sounds and natural sounds in determining their acoustical impact in rural and naturally quiet areas. Amplitude and duration are also important. For example, a bubbling brook and waves crashing into the seacoast may, on average, be equally preferable, even though the amplitude of the latter is much greater than the amplitude of the former.

CPRE, 1995. Tranquility. Campaign to Protect Rural England. Available online at http://www.cpre.org.uk/campaigns/landscape/tranquillity.

Lam, K-C., K-C. Chau, L.M. Marafa, and L. Brown. 2008. Human Preference for Countryside Soundscapes. Presentation at INTER-NOISE 2008, The 2008 International Congress and Exposition on Noise Control Engineering, Shanghai, China, October 26–29. Available online at http://scitation.aip.org/journals/doc/INCEDL-home/cp/.