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beehive_iteration_2015 [2015/04/27 14:19]
ami [Sensors for Vibrations]
beehive_iteration_2015 [2016/01/13 18:48] (current)
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 {{gallery>::​beehive2015:​final-set_up }} {{gallery>::​beehive2015:​final-set_up }}
-After analysis (by Guy De Bièvre) of the recorded soundfiles (2014 project), the conclusion is that there is a bad electrical hum (50Hz and the first harmonic 100Hz) dominating. This probably caused by a power supply somewhere along the line (can be in the hive, but could also be inside near the mixing desk). Best would be to get rid of it physically (finding the guilty source and moving it away from the microphone cables). Another solution (even better if you can combine it with removing the source of the problem) is to shorten the microphone cables by adding a preamp near/in the hive and to start from there on line level, preferably symmetric...simplest way to do that is to get a small mixing desk and set it up near/in the hive and leave from there with a balanced output (a balanced/​symmetric output protects from outside interferences). 
-If you cannot solve this issue physically you should add a 50Hz comb filter patch to the software setup (a 50Hz comb filter will radically/​steeply cut out 50Hz and all of its harmonics (100, 150, 200, 250, etc...))...although,​ when I run the files through a spectrum analyzer I only see the first harmonic (100Hz) clearly, then a much weaker 3rd (150Hz) and a slightly stronger 4th (200Hz), so it should suffice to kill 50, 100, 150 and 200, no need to go above that. (this strongly reduces it, but does not get rid of it altogether, except for the weaker 150 and 200.) 
-I will add screen dumps (to the upload) of the spectrum analyzer, before and after filtering...the hum are those continuous equidistant lines. I ran the  the 4 files you gave me through a FFT 50Hz removal (most software has 50Hz removal presets, because it is such a common issue, though US software will have a, for us useless, 60Hz filter), getting rid of most of the hum and a hi-pass reducing everything below 70Hz, to get rid of the "​city"​ (on one of the samples there is a sound that most likely comes from a car stereo, which is harder to get rid of.) 
-{{:​beehive2015:​50_100_150_200hz_beforrefiltering.jpg|}} {{:​beehive2015:​50_100hz.jpg|}} 
-//​soundfiles before and after filtering// 
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beehive_iteration_2015.txt · Last modified: 2016/01/13 18:48 (external edit)