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Libraries and archives around the world have collections of many thousands of coarse-groove mechanical audio recordings, phonograph or gramophone records, largely 78s or 78 rpm discs. This is a substantial recorded heritage of mankind's music and spoken word made over a period of 65 years. The 78 rpm disc was largely out of production by 1960. These mechanical recordings won't be available indefinitely since the plastics used in their manufacture are deteriorating slowly but steadily. Preservation programs have been underway by a number of organizations. Decreasing costs of digital storage media now make it possible to consider all mechanical audio recordings for transfer to the digital domain. Thus a widespread need was recognized by the Audio Engineering Society (AES) to provide a calibration tool for standard transfer of mechanical coarse-groove audio recordings from the analog to the digital domain.〔Audio Engineering Society Standards Committee, AES 78 rpm Calibration Disc Set (last updated 2007-07-20).〕 The AES coarse-groove calibration discs (AES-S001-064) are a boxed set of two identical discs, one for routine use, one for master reference. The intent is to characterize the reproduction chain for the mass transfer of coarse-groove records to digital media, much like using a photographic calibration reference in image work.〔http://www.aes.org/standards/b_data/x064-rationale.cfm〕 Side A: :Gliding tone, 20 Hz to 20 kHz :Speed: 77.92 rpm :Lateral (mono) coarse groove :Time constants: 3180/450/0 ms :Separate outer & inner bands: ::1 kHz trigger tone ::Gliding tone, 20 Hz to 20 kHz ::1 kHz reference level * ::'' *20 mm Light Band Width (LBW);'' ::''approx 8 cm/s peak-to-peak, 5.7 cm/s rms'' Side B: :Single tones, 18kHz to 30 Hz :Speed: 77.92 rpm :Lateral (mono) coarse groove :Time constants: 3180/450/50 ms (Pressed under license from EMI Records Ltd.) ==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.〔Kendall, Ted. The Front End-EQ Settings, 1996.〕 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? 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Audio Engineering Society, Coarse-groove Calibration Discs」の詳細全文を読む スポンサード リンク
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