[78-L] Removing hiss

[DAVID BURNHAM]

Steven Barr wrote:

Also note that the "surface noise" heard on 78's is caused by the fact that
the shellac-based compound of which they are/were made contains various
"fillers!" The particles of these can be of sizes which, when included in 
the
walls of the grooves, produce their own UNdesired "apparent" sound
signals. The path of a lateral-record groove actually reflects the recorded
waveform; at 78 rpm, the outside turn of the groove spiral is about 9.9*pi
inches long (31.1 inches) which must be traversed in 1/78 of a minute
(1.3 seconds) or c. 23.9 ips. A 50Hz tone has a duration of .02 seconds
so its "wave" in the groove is about .48 inches long at the outside or about
.22 inches long on the inside turn! A 5KHz tone has waveforms .01 times
as long...or .005" outside and .002" inside! These numbers approximate
the sizes of grains of "filler"...meaning there is NO easy way to establish
whether a waveform ,003" long is "surface noise" or is actually part of
the recorded signal...?!

Steven C. Barr 

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I'm not sure what point you're making here but some of your math is a little shaky.  If a record spins at 60 rpm, 1 revolution will take 1 second.  So, obviously, if the record speed is raised to 78 rpm, each revolution will take a fraction of a second, not 1.3 seconds.

db