Pictured: A Neumann Cutting Lathe used to make the record master. Picture courtesy of Bakery Mastering
This is one of the best non-mathematical introductions to the RIAA disc recording playback chain written.
Gallo worked at the Crane School of Music in New York for 30 years as an audio engineer, where he also received a Bachelor of Music in Music Education in 1973 and in 1974 a Master of Arts in Music History. He has contributed many technical articles in professional and DIY Audio publications.
Disc Recording Equalization Demystified
Hello
You mention Gary Gallo, and yes indeed his introduction is very good, but not good enough,
because the picture above is wrong!
The purple signal level is not on the groove, it is the equalisation applied during recording.
But don’t worry, 99% of all the people are wrong.
You all don’t know, that the cutter and the cartridge are velocity transducers, and theses are not linear,
but have 6db cut (cutter) or 6db rise (cartridge) per octave.
This is not the place for a lengthy explanation, but read Gallo carefully and remove this picture.
I make it clear in the article that the pickup is a velocity transducer. However, RIAA EQ splits the audio band into 3 major sections with the mid band section from 500 Hz to 2.12 kHz encoded as constant amplitude. That means the grove displacement is cut at -20 dB/decade in this frequency band and that’s done to make sure that the stylus displacement at the frequency extremes falls within mechanical limits to allow about 20-30 minutes of time on each half of an LP.