[icon-discuss] Re: olympus mikes; last word
- From: Joe Giovanelli <joegio1@xxxxxxxxxxxxx>
- To: icon-discuss@xxxxxxxxxxxxx
- Date: Sun, 25 May 2008 22:35:24 -0400
Hello, Steve,
I noticed that under some circumstances the vibrator would kick in and not
stop. I originally
believed that there was an electrical problem in the PDA. Another party (who I
won't
identify) ran some tests and could not duplicate the runaway problem.
I made tests of my own, as outlined in my message which I think you have quoted
here.
Only the Olympus mike exhibited the problem, which I am sure is attributable
to acoustic pickup between the vibrating PDA and the mike.
At full speed the vibrator produces an audible tone of 250 Hz. This falls
within
a serious response peak of the Olympus mike.
I found that I could run the record level down to between 15 and 20 and I could
make the
system oscillate as described.
It was a bit more difficult to get the oscillation going at these low recording
levels, but it
was possible.
The internal mike never created this same oscillation, but I thought it might.
I got it just
on the edge of positive feedback but I could not actually get the system to go
into sustained
feedback.
This is not to say that the Olympus mike cannot be used with our units. It can
if the mike is
not directly plugged into the mike jack. Olympus thoughtfully provides a cable
which
permits the use of the mike as a lapel mike.
If you use the cable, you'll never have the problem we've been talking about.
I had been fooled for a time to be sure, but finally got to the heart of the
matter. It comes
down to basic physics I guess.
Just to be sure to cover all bases, the Olympus mike has a much higher output
level
than our internal mikes. It would be a project to actually measure the output
of that
mike, and, of course, there's no way to measure the output voltage of the
internal mike.
We'd need a sound source of known SPL and we'd that same SPL for both mikes.
I'll gladly leave that to others.
I believe that we can be absolutely certain that the runaway vibrator can be
explained as
I have outlined.
If we want to be very scientific (and I don't), anyone who has one of the
Olympus
mikes can easily duplicate my tests.
I'm not at all sure that conducting these experiments might eventually damage
our units because
we're doubtless saturating the whole recording chain and we don't know how
delicate the
system is when subjected to this kind of stress.
Joe G.
On Sun, 25 May 2008 21:39:06 -0400, Steve Dresser wrote:
>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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