the response from The Echo Nest's demo song search, but with the audio_summary bucket (also, I prettified it for readability) - fetched from http://developer.echonest.com/api/v4/song/search?api_key=N6E4NIOVYMTHNDM8J&format=json&results=1&artist=radiohead&

karmapolice.json

{"response": 
  {"status": 
    {"version": "4.2", 
     "code": 0, 
     "message": "Success"}, 
   "songs": [
     {"audio_summary": 
       {"key": 7, 
        "mode": 1,  
        "time_signature": 4, 
        "duration": 264.05986000000001, 
        "loudness": -9.8900000000000006, 
        "energy": 0.27011595863752474, 
        "tempo": 74.932000000000002, 
        "audio_md5": "e83e23ecdcff45e68fa1bd086346eea1", 
        "analysis_url": "https://echonest-analysis.s3.amazonaws.com/TR/e1DqxQFjPF9zYBPll8rbzjeFqw5DwMAckXQvAH/3/full.json?Signature=rZse8QKKrnMrnKG1Zy3YMaResOY%3D&Expires=1340982900&AWSAccessKeyId=AKIAJRDFEY23UEVW42BQ", 
        "danceability": 0.4243152022634028}, 
      "artist_id": "ARH6W4X1187B99274F", 
      "id": "SOHJOLH12A6310DFE5", 
      "artist_name": "Radiohead", 
      "title": "Karma Police"}]
  }
}