I just looked back at some notes and found that the amplifier 
was inverse hyperbolic sin (not tangent).  Analog Devices made
755N and 755P log and antilog amplifiers that used ARCSINH 
compression and decompression.  

This compression function is described in a BSSA paper by
Francis Wu and Ernest Jarrold (BSSA, V 64, No. 5, pp 1591-1594.

JCLahr


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