Hi slegroux, guitarded. We are always working to improve our analysis algorithms, so you may see changes to date now and then. If you look at the detailed analysis (pointed to by the analysis_url in the audio_summary), you'll find a metadata block that includes the analysis version:
"meta": {
"analyzer_version": "3.1.1",
"detailed_status": "OK",
"filename": "/mnt/mp3/025545615.mp3",
"artist": "",
"album": "",
"title": "",
"genre": "",
"bitrate": 208,
"sample_rate": 44100,
"seconds": 207,
"status_code": 0,
"timestamp": 1341602264,
"analysis_time": 33.09159
},
You can use the analysis version to learn if and when the analysis has changed. We will also post to announcement forum on any future analysis updates with details on the changes so you won't be surprised if/when values change.