M2TECH Joplin - Manual (Page 30)

JOPLIN
384
k H z /32bit ANALOG-TO-DIGITAL CONVERTER
REVISION P R B – SEPTEMBER 2012
Copyright © 2012, M2Tech Srl
30
M2Tech
www.m2tech.biz
9. Notes on equalization
9.1. Why equalization is needed for records?
When cutting a record, two problems must be faced: the dynamic of the media, which is
related to the groove width and depth, thus to the record diameter and thickness, and the
surface noise. As low frequency tones tend to cut large, deep grooves, dynamic limits are
likely to be hit due to the low frequency content of the music being cut into the vinyl. On
the other hand, high frequency tones have generally low amplitude, thus they are likely to
be covered by surface noise.
To solve the above problems, an equalization is applied to the signal before sending it to
the cutting lathe: low frequencies are attenuated to reduce their dynamic and high
frequencies are amplified to elevate them over the surface noise floor.
Of course, the reversed equalization is applied to the signal coming out of a cartridge while
reading a disc: low frequencies are amplified and high frequencies are attenuated
(together with the surface noise which becomes less apparent).
Presently, all records are cut using the RIAA curve (Figure 22), which has been proposed
as a standard back in 1954. Both low frequencies amplification and high frequencies
attenuation for playback are clearly visible.
RIAA playback curve
0
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,5 16 20 25
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,5 40 50 63 80 10
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Hz
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Figure 22