[icon-discuss] Re: olympus mikes; last word

Joe,
There are a couple of contributing factors here. First, if the output of the Olympus mic is higher than that of the internal mic, you'll have to reduce the level more before the vibrator will stop. Second, the Olympus mic may have a peak in its response curve that corresponds to the frequency of the vibrator. In order to determine what's really going on here, you'd have to start with a source whose frequency response you had already measured. You'd also have to consider acoustic factors like the response of your room, and heaven knows what else. In essence, you're trying to answer a question for which you don't have the proper equipment to make useful measurements. Besides, you don't even have a good way to determine the exact threshold where the vibrator kicks in and out. 

Steve
----- Original Message ----- From: "Joe Giovanelli" <joegio1@xxxxxxxxxxxxx> 
To: <icon-discuss@xxxxxxxxxxxxx>
Sent: Wednesday, May 21, 2008 19:10
Subject: [icon-discuss] olympus mikes; last word


Hello Listers,

I could have chosen a different subject for this message.
We have discussed using the Olympus mikes with our PDA'S. Yes, it's convenient to plug it right in, and we can start recording. Without equalization we will not get really great 
recordings.  That's just the first negative!
I sent a message about a situation in which, if the signal level was too high, that the vibrator would come on and not stop without intervention. That can be true, but not in all cases.
I ran some pretty exhaustive tests to try to bring about this same problem. I set the recording level to 63, and the unit was set to record from the internal mike. If I held the unit near my mouth, the slightest sound would begin to excite the vibrator. I tapped the case and the vibrator really got going. It stumbled around, but eventually settled down. I yelled into the mike, with the the same result, except that the vibrator ran even 
longer before calming down.

If I used the Olympus mike, I could reduce the level to perhaps 40.  If I
tapped the case again, the vibrator ran full tilt and would not stop till I either paused 
or stopped the recording.

Why is this?  The Olympus mike has absolutely no shock absorption!  When the
vibrator gets going, it obviously makes the unit vibrate. This vibration is passed to the mike, and this adds to the original signal and the vibrator runs even faster. This 
regenerative action continues till the vibrator runs full bore!
The internal mike tries to do the same thing, but not as severely as is true of the Olympus 
mike.

External mikes won't cause this condition.
This proves there's no problem with our units. It's the Olympus mike which is the problem.
Conclusion: When using the Olympus mike, be careful not to jar your PDA or you might start this self-oscillation. You must be sure to keep the level low enough so that the vibrator does not come into play. For really loud music, I find that 20 or 15 is good for recording. I use the internal mike for meetings. If I'm close to the speaker, I set the level 
to about 40.
I don't really like recording above this because the preamp noise floor gets too high. 

Joe G.


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