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mediatechnology
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International Association of Sound and Audiovisual Archives

Post by mediatechnology » Sat Nov 07, 2015 5:49 pm

Guidelines on the Production and Preservation of Digital Audio Objects

http://www.iasa-web.org/tc04/audio-preservation

Sections 5.2 and 5.3 are very interesting and provide EQ curves for vintage and LP microgroove playback. http://www.iasa-web.org/tc04/signal-ext ... l-carriers
5.2.6.8 It is worth noting that a flat transfer will require around 20dB more headroom than one where an equalisation curve has been applied. However, as the potential dynamic range of a 24 bit digital to analogue convertor exceeds that of the original recording, the extra 20dB headroom can be accommodated.
Based on my experience 20 dB seems about right.
5.2.6.9 Apart from the dynamic range limitations mentioned above, a drawback with transferring electrically recorded discs without de-emphasis is that stylus selection is primarily made through aural assessment of the effectiveness of each styli, and it is more difficult, though not impossible, to make reasonable assessment of the effect of different styli while listening to unequalised audio. An approach taken by some archives is to apply a standard, or house, curve to all recordings of a particular type in order to make stylus selection and other adjustments, and subsequently produce a simultaneous flat and equalised digital copy of the audio. As the exact equalisation is not always known, a flat1 copy has the advantage of allowing future users to apply equalisation as required, and is the preferred approach.
5.2.6.10 There is some debate as to whether noise reduction tools for the removal of audible clicks, hiss etc are more effective when used before an equalisation curve is applied rather than afterwards. The answer very likely varies according to the specific choice of tool and the nature of the job to which it is applied, and in any event will be subject to change as tools continue to evolve. The most important point in this regard is that noise reduction equipment, even fully automated tools with no user-definable parameters, ultimately employs subjective and irreversible processes, and so should not be used in the creation of archival master files.
5.2.6.9 and 5.2.6.10 make good arguments for both flat and RIAA EQ'd outputs.
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