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Digitization of Magnetic Audio Tape

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Digitization of Magnetic Audio Tape Digitization of Magnetic Audio Tape Matthew Wilcox, Audiovisual Archivist Michigan State University Archives & Historical Collections Topics which will be discussed: Brief history of magnetic audio tape Descriptions of various types of audio tape media Brief information on digital audio terminologies Setup of playback equipment for digitization Creating an analog to digital audio workflow Creating a preservation file and derivatives Suggestions for providing metadata Topics which will NOT be discussed: In-depth discussion of make-up of magnetic audio tape Suggestions for fundraising for digitization projects A brief history… 1928 – Dr. Fritz Pfleumer gets a patent in Germany for application of magnetic powders to strip of paper or film 1931 – Pfleumer and AEG (Allgemeine Elektricitäts-Gesellschaft) begin to construct the first magnetic tape recorders 1945 – Signal Corps Captain John Mullin finds Magnetophones at Radio Frankfurt in Germany and 1000-meter reels of 6.5mm ferric- coated BASF tape with 20-minute capacity; mails 2 machines to the U.S. with 50 reels of tape, and after the war works on them to improve the electronics A brief history (continued)… 1946 – Major Mullin demonstrates the 2 Magnetophones, with modified electronics, to the Institute of Radio Engineers in San Francisco 1947 – Murdo McKenzie, Bing Crosby’s technical producer, arranges to have Crosby’s Philco Radio Time show recorded on tape by Mullin’s tape recorder, and compares it with recordings by another engineer, and a recording on transcription disc. The recording on Mullin’s device was preferred, earning a contract to record and edit Crosby’s radio program. Crosby invests $50,000 in Ampex, the company now distributing Mullin’s recorder, to expand production. Bing Crosby Productions becomes its West Coast distributor Common types of magnetic audio ¼” open reel audio tape Common types of magnetic audio cassette / cartridge-based audio tape compact cassette Why digitize magnetic audio tape? Open reel tape players and compact cassette decks are obsolete forms of media Magnetic tape, even in ideal storage situations, can deteriorate Sticky Shed Syndrome, a breakdown in the binders of the tape, can harm not only the tape but the playback equipment as well For open reel audio tape, slowly turn the reel to see if the tape unspools naturally. If the tape sticks to itself in the pack, your tape is affected and should not be run through playback equipment Digital audio files can be made accessible online, and will maintain the integrity of the original carrier Temporary fixes for affected tape “Baking” the tape in a convection oven on a low heat for 8+ hours removes moisture from the binder. However, this can be destructive if not handled properly, and is best done by a professional audiovisual conservator or technician using a highly precise oven “Baking” is a temporary fix for the tape itself, but will allow a window of opportunity for digitizing A less risky, but far less immediate method of hydrolysis reversal is environmental conditioning. Placing the tape in a low humidity environment long enough for the effects of hydrolysis to recede can also be an effective means of preserving the tape Hess, R. (2008). Tape degradation factors and challenges in predicting tape life. ARSC (Association for Recorded Sound Collections) Journal, 39(2), 240-274. Retrieved from: http://www.richardhess.com/tape/history/HESS_Tape_Degradation_ARSC_Journal_39-2.pdf Basic parameters of digital audio Format Broadcast Wave Format (BWF; .wav) is an extension of the popular Microsoft WAVE audio format and is the recording format of most file- based non-linear digital recorders used for motion picture, radio and television production. BWF is a .wav audio file format, and a container format Retrieved from https://www.wikipedia.org/wiki/Broadcast_Wave_Format Encoding Uncompressed Linear Pulse Code Modulation (LPCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications Retrieved from https://www.wikipedia.org/wiki/Pulse-code_modulation Basic parameters of digital audio Sampling rate The number of times the analog sound is sampled during each period (one complete waveform) and converted into digital information. This is represented in Kilohertz (kHz). A popular sampling rate, 44.1kHz, is the rate used for compact discs (CDs). The larger the sampling rate, the closer the digital version compares to the original analog recording. Bits per sample How much information (number of amplitudes) in each sample the computer is collection. A sampled sound is converted into an equivalent digital value. The sample rate used for CDs is 16-bit. The higher the bit rate, the higher the quality of digitized sound. Best practices for archival preservation? Broadcast Wave Files (BWF, or .wav files) are the preferred file format, but best practices for sampling rate and bit-depth vary among organizations and institutions. Some say that 48kHz/24-bit is satisfactory for preservation master files. Others prefer 96kHz/24-bit (I use this at MSU Archives) Working/Production master files (or “mezzanine” files) are recommended for copying onto recordable CDs. Since traditional CDs are recorded at 44.1kHz/16-bit, this is recommended for this tier (also .wav files) Access files are created for online access of digital audio files. The recommended sampling rate is also 44.1kHz, with the quality (in kilobytes per second, or kbps) varying. 160 or 192 kbps is sufficient (.mp3 file) Setup of playback equipment …will be shown at the demonstration(s) at the end of the workshop! Workflow 1. Define your materials What types of carriers are in your collection? How many items are in your project? Are they the same format? What are the extents of your materials? e.g. 12 open-reel audio tapes. Varying lengths of tapes. All tapes were recorded at 7 ½ ips Workflow 2. Method of digitization and technical specifications Digitizing in-house, or outsourcing? Do you have the equipment you’ll need? File types? Formats? e.g. Digitizing all tapes in-house, creating 96kHz/24-bit preservation .wav files, 44.1kHz/16-bit working .wav files, and 44.1kHz .mp3 files at 192 kbps Workflow 3. How will you provide access to your deliverables? What is your platform for making .mp3 files accessible? What is your workflow for transferring, saving and uploading digital files? Does your workflow support access goals? e.g. .mp3 access files with basic metadata will be made available online for public access Workflow 4. Define your metadata schema and workflow Define your fields How will metadata be entered? How will metadata be collected and created? e.g. Modified Dublin Core metadata standards will be used. An Excel spreadsheet will collect initial metadata prior to digitization, and additional information will be added during digitization as needed Workflow 5. Define a file-naming convention and determine where files will be stored File names should be unique and consistent Keep file structure organized within folders as your project grows Workflow 6. Perform quality control (QC) QC should occur during all stages of your project Establish consistent, regulated procedures for performing QC 7. Track digitization and documentation processes 8. Written procedures for entire digitization process should be well- documented, and shared with entire staff working on your project Metadata: Audacity (https://sourceforge.net/projects/audacity) Artist Name Track Title Album Title Track Number Year Genre Comments Additional customized tags may be added Metadata: Dublin Core DC Element: Title DC Definition: A name given to the resource Audiovisual Interpretation: The main title associated with the recording DC Element: Subject DC Definition: The topic of the resource Audiovisual Interpretation: Main topics covered Metadata: Dublin Core DC Element: Description DC Definition: An account of the resource Audiovisual Interpretation: Explanatory notes, interview summaries, descriptions of environmental or cultural context, list of contents DC Element: Creator DC Definition: An entity primarily responsible for making the resource Audiovisual Interpretation: Not authors or composers of the recorded work but the name of the archive Metadata: Dublin Core DC Element: Publisher DC Definition: An entity responsible for making the resource available Audiovisual Interpretation: Not the publisher of the original document that has been digitized. Typically the publisher will be the same as the Creator DC Element: Contributor DC Definition: An entity responsible for making contributions to the resource Audiovisual Interpretation: Any named person or sound source. Will need suitable qualifier, such as role (e.g. performer, recordist) Metadata: Dublin Core DC Element: Date DC Definition: A point or period of time associated with an event in the lifecycle of the resource Audiovisual Interpretation: Not the recording or ℗ (sound recording copyright) date of the original but a date relating to the resource itself DC Element: Type DC Definition: The nature or genre of the resource Audiovisual Interpretation: The domain of the resource, not the genre of the music. So Sound, not Jazz Metadata: Dublin Core DC Element: Format DC Definition: The file format, physical medium, or dimensions of the resource Audiovisual Interpretation: The file format, not the original physical
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