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Entry  Thu Jul 9 19:05:32 2009, Clara, Update, PEM, more mic position changes; mics not picking up high frequencies 6x
    Reply  Thu Jul 9 19:24:50 2009, rana, Update, PEM, more mic position changes; mics not picking up high frequencies 
Message ID: 1728     Entry time: Thu Jul 9 19:05:32 2009     Reply to this: 1729
Author: Clara 
Type: Update 
Category: PEM 
Subject: more mic position changes; mics not picking up high frequencies 

Bonnie has been strung up on bungees in the PSL so that her position/orientation can be adjusted however we like. She is now hanging pretty low over the table, rather than being attached to the hanging equipment shelf thing. Butch Cassidy has been hung over the AS table.

Moving Bonnie increased the coherence for the PMC_ERR_F signal, but not the MC_L. Butch Cassidy doesn't have much coherence with either.

I noticed that the coherence would drop off very sharply just after 10 kHz - there would be no further spikes or anything of the sort. I used my computer to play a swept sine wave (sweeping from 20Hz to 10kHz) next to Butch Cassidy to see if the same drop-off occurred in the microphone signal itself. Sure enough, the power spectrum showed a sharp drop around 10kHz. Thinking that the issue was that the voltage dividers had too high impedance, I remade one of them with two 280 Ohm and one 10 Ohm resistor, but that didn't make any difference. So, I'm not sure what's happening exactly. I didn't redo the other voltage divider, so Bonnie is currently not operating.

 

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