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Topic: the situation is worse than you thought
Replies: 10   Last Post: May 4, 2013 11:58 AM

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Jeff Liebermann

Posts: 13
Registered: 9/13/07
Re: the situation is worse than you thought
Posted: May 2, 2013 1:10 AM
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On Thu, 02 May 2013 02:53:01 GMT, benj <benj@iwaynet.net> wrote:

>My favorite whine has to do with electret mics. Time was (time for old-
>timers reminisce magazine review) when AT&T spent a LOT of effort
>perfecting telephones. Heavy. Indestructible. Totally sonically tweaked
>for intelligibility. You couldn't kill one and you actually could
>understand the person on the other end...pretty much no matter what.


You have a short memory. The old AT&T (Western Electric) were solidly
built, but could still be killed. The dials required lubrication
every few years. The carbon mics would "pack". I had to pound them
on the table before talking. It was standard practice for carbon
dispatch microphone to be banged on the table before transmitting.
Some also sucked enough current that they got warm. The old telco
handsets were made from bakelite, which is durable, but also
expensive. If I tried to manufacture a WE model 500 phone today, it
would probably need to sell for over $200, mostly due to the high
labor content.

>Then all of a sudden all of what I call "real phones" disappeared and
>cheap plastic versions with electret mics appeared. Now you'd THINK that
>a nice wide band electret mic would sound better. And at first it does.
>But soon they all seem to develop a severe case of overload distortion
>and it makes conversations all guesswork.


It's not overload distortion, whatever that means. Some electret mic
capsules simply lose their charge. Basically, an electret mic is a
condenser (capacitor) microphone, without the external power supply to
charge the condenser. If the charge partially leaks away, the mic
will sound awful. I don't think you can proclaim all such electret
mics to be defective. Of the huge number of electret microphones I've
seen in numerous radios, headsets, computer mics, and cell phones,
I've identified maybe a half dozen as defective and easily replaced
them. There may be a problem with some electret mics, but it's
nowhere as bad as you make it seem.

>Oddly nobody seems to notice this problem!

True. That's because there is no problem.

>And it's not just my kitchen phone that looks like a banana
>that does this, it's lots of large business systems. So you try to place
>an order and all you get is mush. My doctor's phone is like that. I swear
>I'm going to have to buy him a new phone so I can talk to him!


You might try cleaning out the wind screen in front of the electret
capsule before buying a new phone. Saliva and dirt do a wonderful job
of blocking the audio path.

>I remember even as a kid when my ears still worked well, the cop would
>get a call on the police radio and all I'd hear is:
>Razzafrazzasbuzzarumblebuzz, but the cop would somehow understand it all
>perfectly and respond: "You bet! I'll be there in 15 minutes!" I'd be
>amazed! "How does he DO that," I'd wonder?


That's different. Your hear needs to become accustomed to decoding
the voice in the presence of noise. Anyone who uses a radio initially
has the same problem. Actually, anyone who visits a foreign country
also has a similar problem. Everything initially sounds like noise or
garble. Extracting intelligence from the noise is difficult.
Eventually, the human ear (and brain) adjusts, and the intelligence
becomes much easier to extract. I had this problem when I switched
from designing FM marine radios to HF SSB radios. I couldn't
understand anyone talking on the HF radios. After a few weeks of
listening to HF SSB, I couldn't understand anyone on the FM radios. Oh
well. If you listen on the scanner long enough, you should eventually
be able to extract the speech from the noise.



--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558



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