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From: telecom@ucbvax.UUCP
Newsgroups: mod.telecom
Subject: Telephone Distortions
Message-ID: <8512261347.AA00137@epiwrl.uucp>
Date: Thu, 26-Dec-85 08:47:25 EST
Article-I.D.: epiwrl.8512261347.AA00137
Posted: Thu Dec 26 08:47:25 1985
Date-Received: Sat, 28-Dec-85 18:13:47 EST
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Approved: telecom@mit-xx.arpa


	I am investigating the electrical characteristics of current 
telephone handsets and speakers.  (It used to be easy, but these 
days you can't count on having a carbon button mike and a ring-armature 
earphone!) I would like to know the following.

1. Which transducers are the major suppliers of telephones  for 
commercial applications (such as AT&T, ITT, GTE, TIE, etc) using in their 
handsets and speaker phones? Also, who are the manufacturers of 
these transducer units?
 
2. What are the advantages and disadvantages of these newer transducers over 
the standard units (carbon button and ring armature)? 

3. What analog signal processing occurs in electronic telephones?

4. Where can I get technical details (such as magnitude and phase response, 
harmonic distortion, and directivity) about these transducers?



	On a different topic, how do PBXs, local loop circuits, and 
long distance circuits affect analog voice channels.  I am particularly
interested in identifying the types of circuit or switching that do 
the following: (1) distort the passband frequency response, (2) distort the 
envelope delay, and (3) add transient phenomena, such as impulse noise 
or dropouts. 


	I would appreciate specific information, references, pointers, etc.  
Thanks for you help.


                                      David Burton
				      Entropic Processing Inc.
	


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