While the tags are “individual”, the audio fields seem to be interconnected on the morphic plane. The longer an audio field has existed, (I think) it grows more and more and anyone who listens to it experiences the cumulative strength. Also, as more and more users listen, the audio field continues to grow stronger as it is the same field transmitted through various copies of the Mp3 file and hence impacted by collective usage. This does not seem to be true with Dog tags - which are localized to the physical object and the wearer.