Monday, September 24, 2012

Fast is Fine, But Accuracy is Everything

Previously we proposed there are five fundamentals of high-quality digital sound archiving and preservation for analog source material: accuracy, adequacy, appropriateness, consistency, and explicitness.

Today we tackle the first fundamental, accuracy (with regard to the source).

Consider this. Carole King's The Legendary Demos is now available in 24-bit/96kHz high definition. Demos. In high-def. Does that make any sense? Actually, it makes perfect sense, and illustrates the importance of accuracy.

Demos, as you probably know, are recordings of stripped-down arrangements songwriters use to "pitch" material — to producers, bandmates, potential clients. A promise of a song rather than the song itself. Neither professionally recorded nor mastered, the audio quality of a demo varies widely. And great songwriters are not always great performers (with notable exceptions).

The material on The Legendary Demos is true to the form. Many of the tracks sound as if they are simply Ms. King at the piano in her office. Recorded on 60s vintage analog equipment, the sound level is uneven, the piano not balanced with the vocal (the piano perhaps unmiked). So why go high-def?

The first reason is simply to master the material for release to give it as much polish as possible. (It sounds better here than on what may have been the original tapes aired during an April 2012 Fresh Air interview with Ms. King). Second and more importantly, these recordings document the creative process which produced songs that went on to become big hits. How does one preserve such moments for posterity so they are not lost or forgotten?

The International Association of Sound and Audiovisual Archives (IASA) "Guidelines on the Production and Preservation of Digital Audio Objects" offers these recommendations:
  • Sampling rate. When producing digital copies of analogue material IASA recommends a minimum sampling rate of 48 kHz for any material. The unintended and undesirable artefacts in a recording are also part of the sound document [and] must be preserved with utmost accuracy. For certain signals and some types of noise, sampling rates in excess of 48 kHz may be advantageous. IASA recommends 96 kHz as a higher sampling rate, though this is intended only as a guide, not an upper limit.
  • Bit depth. IASA recommends an encoding rate of at least 24 bit to capture all analogue materials. For audio digital-original items, the bit depth of the storage technology should at least equal that of the original item. It is important that care is taken in recording to ensure that the transfer process takes advantage of the full dynamic range.
Record analog source material for digital archiving with as many bits as you can muster. Preserve numeric precision (and hence dynamic range) in the audio processing pipeline. Establish and follow a plan that preserves the accuracy of the material presented.

[Originally published 10-May-2012. Revised and expanded.]

             Vinyl-to-Digital Restoration #32            

Artist: Carole King
Title: Tapestry
Genre: Pop
Year: 1971

If you are of a certain age, this is the album your sister and every woman you ever dated (my wife included) had in her collection . At one time, the best selling album in history, and Carole King the only female performer to win four GRAMMY® awards in one year. Legendary.

© 2012 Thomas G. Dennehy. All rights reserved.

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