Audio Engineering Society, Coarse-groove Calibration Discs - A Closer Look at The Preservation Problem

A Closer Look At The Preservation Problem

According to Ted Kendall, maker of the Front End audio restoration unit also known as "The Mousetrap", the equalization time constants for post-1955 78s used in the Front End are 3180/450/50 ms. These time constants are identical to those used in the AES Coarse-groove Calibration Discs. Since the 78 rpm record would be obsolete by 1960, this means that there is a very large population of pre-1955 78s requiring different equalization settings depending on the vintage and label of the disc.

Type of Recording: Equalizer Settings
Acoustic recordings (pre-1925): Flat/AC/AC
FFRR 78s: Flat/636/25
EMI 78s 1945-1955: Flat/636/Flat
Most other UK 78s 1925-1945: Flat/531/Flat
Post-1955 78s: 3180/450/50
BBC direct recordings 1945-1960: Flat/BBC/BBC
CCIR standard coarse-groove transcriptions: Flat/450/50
AES (some early US Lps): Flat/400/63.6
Modern LPs (RIAA equalization): 3180/318/75
Lateral cut NAB transcriptions: 2250/250/100
Vertical cut NAB transcriptions: Flat/531/40*
Western Electric 78s: Flat 531/Flat*
  • Adjustments needed*

So, the dilemma is this: should coarse-groove recordings be transferred in mass to digital using an arbitrary phonoequalization curve such as with the AES calibration discs, or should each recording be matched to the curve appropriate to its vintage and label, then transferred to digital media?

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