  Urban sound has a huge influence over how we perceive places. Yet, city
planning is concerned mainly with noise, simply because annoying sounds come to
the attention of city officials in the form of complaints, while general urban
sounds do not come to the attention as they cannot be easily captured at city
scale. To capture both unpleasant and pleasant sounds, we applied a new
methodology that relies on tagging information of geo-referenced pictures to
the cities of London and Barcelona. To begin with, we compiled the first urban
sound dictionary and compared it to the one produced by collating insights from
the literature: ours was experimentally more valid (if correlated with official
noise pollution levels) and offered a wider geographic coverage. From picture
tags, we then studied the relationship between soundscapes and emotions. We
learned that streets with music sounds were associated with strong emotions of
joy or sadness, while those with human sounds were associated with joy or
surprise. Finally, we studied the relationship between soundscapes and people's
perceptions and, in so doing, we were able to map which areas are chaotic,
monotonous, calm, and exciting.Those insights promise to inform the creation of
restorative experiences in our increasingly urbanized world.
