In reading Bell System histories, it appears that they purposely narrowed the bandwidth provided for voice long distance calls so as to increase the capacity of circuits. During the war, the phone system was under extremely heavy use.
Would anyone know more about this and when it was concluded? Apparently it remained after the war because new DDD signalling efforts caused a problem.
IIRC, the normal bandwidth for telephone voice is about 4 KHz. I'm not sure how much the narrowed it or what part of the bandwidth they took off (I think it was the upper end), so perhaps the bandwidth was
2.5 KHz.I wonder how much it affected clarity.
There was a definite noticeable difference in voice quality between the 1938 302 set and prior sets. Indeed, the 202 "French" telephone and "candle stick" telephone were retrofit with 300 components--the French telephone got an "F" handset and the candlestick got new 300 type transmitter and receiver. (There is a slight change in appearance of the transmitter external cup when so modified, it is wider and much flatter.)
However, when war broke out the 302 was pretty new and likely the vast majority of subscribers had older telephones. Accordingly, clarity wasn't so great to begin with.
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On 1/21/43 the Bell System lowered long distance rates. The initial period of 3 minutes remained the same. However, overtime per minute rate went down from 1/3 to 1/4 the cost of the initial period. So if the initial period is $1.20, overtime was 40c and became 30c. I believe this protocol remained in place until 1 minute periods were introduced in the 1970s.
During the war the Bell System had a major ad campaign asking people NOT to use the phone, especially long distance. If one had to use it, limit the call to five minutes.
[TELECOM Digest Editor's Note: About the same time, the federal government nationalized Western Electric and diverted WECO entirely into wartime production of its own equipment needs. AT&T also asked subscribers to give up any extension phones on their lines (although they did not require it) for the reason the reason that Bell needed phones to supply new customers with instruments. PAT]