Magnetic Media Workshop. History

Transcription

1 Magnetic Media Workshop History Magnetic Tape 70th Anniversary Article Steven Schoenherr - The History of Magnetic Recording History Channel Magnetic Tape Preservation Richard Hess - Tape Degradation Factors and Challenges in Predicting Tape Life University of California Santa Cruz Josephson Engineering Inc, (Audio Equipment Manufacturer) History of Magnetic Recording Tape 1844: Samuel Morse sends an encoded, electronic signal across a wire from Washington to Baltimore 1876: Alexander Graham Bell demonstrates that sound can be turned into an electric current and back again.

2 1877: Thomas edison invents the Cylinder Phonograph which uses a needle to etch a groove on a tinfoil cylinder. Later became a wax cylinder Wax Cylinder Recording : Emile Berliner releases first commercial record player, the Gramophone. Uses flat disks instead of cylinders. 1898: Valdemar Poulsen invents the Telegraphone in Denmark. Uses a wire covered cylinder 1900: Poulsen recorded the voice of Emperor Franz Joseph at the Paris Fair. Preserved in the Danish Museum of Science and Technology as the oldest magnetic sound recording

3 Wire Recorder Demo: : American Telegraphone Company acquires Poulsen s patent and starts producing dictation machines. Over the next 30 years various wire recorders are developed. Cylinders, records and wire recorders are being produced by multiple companies for several decades. The film industry adopts optical sound recording printing audio patterns directly onto film. 1928: Germany. Fritz Pfleumer patents Sounding Paper, paper tape coated with iron oxide.

4 1932: Pfleumer teams with CEO of AEG (German: General Electricity Company), Hermann Buchar, and chemists from BASF (a chemical company producing plastics and films) to develop a tape recorder. It uses carbonyl iron powder with a base layer of cellulose acetate. 1935: The Magnetophone debuts at the Berlin radio fair.

5 First tape recorded with 1934 AEG Magnetophon prototype : Major John T. Mullins brings 2 Magnetophones and 50 reels of BASF tape home from Germany. He presents them to the Ampex Corporation (who make motors and machinery) Ampex uses FIAT reports of the U.S. Government Intelligence Agency Reports on German industries to gain more information to develop its own tape recorder design. 1946: The FIAT reports of the German BASF tapes caused the 3M company to create a magnetic tape laboratory. 1947: Bing Crosby is recording with transcription disks at the new ABC network. He samples Mullins Magnetophone and invests $50,000 in Ampex to expand production. Broadcasters begin to adopt tape over transcription disk in the following years. 3 Main Types of Tape - Audio - Video - Data Tape - What is it? 1. Base Film 2. Binder/oxide coating (includes lubrication) 3. Back coating

6 Base film. - Plastic Polyethylene Terephthalate (PET). Trade name:mylar. - Polyethylene Naphthalate (PEN) - For: DAT, Data, some Video. - Older audio reels may be PVC or acetate. Oxide Coating - Oxide: A mix of magnetic particles, usually mostly iron or chromium. Fine powdered metal, like a dust. - Binder. Glue that holds the oxide particles to the base film. Polyester Urethane/Polyurethane - Lubricant is added to the binder oxide mix to reduce friction in playback. Multiple binder/oxide formulations have been utilized. The major focus has been on the magnetic performance of the oxide with special regard to increasing the overall dynamic range of the tape. In order to achieve this wide dynamic range, other portions of the binder/oxide/lubricant component were modified to allow a larger percentage of magnetic particle fill. Sometimes these new formulations created both short-term and long-term degradation modalities as evidenced by newer tapes aging more rapidly than older tapes. - Hess

7 - Dynamic range - low and high signals Key Issue: Many companies have formulated proprietary tape coatings. They age and degrade differently. Big Players: - BASF - Ampex - Sony - Scotch/3M During playback lubricant is squeezed to the surface and should return back to the reservoir.

8 Back Coating - Reduce friction during playback and winding. - Provide strength and rigidity to the tape Key Issue: Many companies have formulated proprietary tape coatings. They age and degrade differently. Big Players: - BASF - Ampex - Sony - Scotch/3M During playback lubricant is squeezed to the surface and should return back to the reservoir. Identifying Brands - Open reel tape is rarely branded - Any branding is typically only located on the reel. - Many tapes are in white unbranded boxes. - Reels are interchangeable: played from one reel to another then wound back. Even if the tapes were easily identified, we still do not have access to the detailed chemical and physical specifications of the tapes since these have always been considered trade secrets. A detailed survey of that information is likely never to be forthcoming. Reverse engineering the chemical and physical properties from degraded samples is often the best that can be done. - Hess Audio Tape Recording

9 A magnetic recorder receives an electrical signal which it uses to stimulate the field of an electromagnet. This creates an impression on the tape. Microphone - A transducer. A device that can turn information from one type to another. A video camera could also be considered a transducer. Sound waves cause movement of a thin metallic diaphragm and an attached coil of wire. A magnet produces a magnetic field which surrounds the coil, and motion of the coil within this field causes current to flow. Fidelity - Accuracy with which a microphone can turn air pressure patterns into electrical current.

10

11 The tape is held tightly against the capstan by the pinch roller and dragged across the three heads at a steady rate. The heads are electro-magnets. If a current is passed through the head a field is produced which creates a magnetic spot on the tape. The amount of magnetism will be proportional to the amount of current. Magnetic spots in succession are called a track. Audio Tape Speeds and Sizes Speeds Widths Tracks 30 ips 2" ips 1" /2 ips 1/2" /4 ips 1/4" /8 ips 1/8" 2-8 General rule: the wider tapes are run at the faster speeds Most Common Audio Tapes: - ¼ open reel tape with 2 tracks (left and right) running at 7 ½ or 15 ips. - ⅛ cassette with 4 tracks running at 1⅞ ips - DAT tape (Digital Audio Tape)

12 Video Tape Recording - NTSC: 525 lines of resolution fps (Decades worth of recorders, only one kind of TV) - Video tapes carry multiple signals. - Luma or Y. The Black and white signal - Chroma - Left Channel Audio - Right Channel Audio - Requires time base correction - device that buffers video and syncs entire system Tape Heads and Track Configurations The control track encodes a series of pulses, each pulse corresponding to the beginning of each frame. This allows the video tape player to synchronize its scan speed and tape speed to the speed of the recording -

13 2 Quad Open Reel 1951: Ampex began working on a video tape recorder. The Ampex VTR-1000 became commercially available in Sold $4.5 million in units in first week. - Shortly after they begin experiments with helical scan recording - Uses 2 3M tape stock - Referred to as 2 Quad or just Quad. Short for quadruplex, it uses 4 heads. - Runs at 15 ips - Holds about 1 hour per tape - 3 Varieties: - Low Band: Original 1956 model - High Band: uses a wider more powerful signal, replaces low band - Super High - Later models could play all three types, however, earlier low band models can t play high band.

14 1 Type A Open Reel 1965: Ampex releases 1 Type A open reel video tape. Was not industry standard as it did not meet Federal Communications Commission(FCC) specifications for broadcast videotape formats. The only format passing the FCC's standard is 2-inch quadruplex. - Uses helical scan

15 Helical Scan - Allows the head to make contact with a larger area of tape. Much longer signals can be recorded to the tape. -

16 1 Type C Open Reel - Sony, Replaces 2 video for broadcasters. - Smaller unit with smaller tapes. - This unit ships with scopes, a monitor and a time base corrector. Basically a broadcast recording studio all in one package. - Very high quality. Superior to Umatic and comparable to Betacam SP (both later technologies) - Also used for mastering to LaserDisk and VHS

17 ½ Open Reel CV (Consumer Video) and AV (EIAJ Type 1) Formats - Sony, Used by schools, businesses artists, theater, dance companies. - Very common, widely used format. - Tapes did not age well. - Not great quality. - CV and AV formats are not interchangeable. AV replaced CV

18 ¾ Umatic Cassette - Sony First broadcast cassette - Intended to be a consumer - Not widely used by broadcasters. Schools, local television, industrial video, home production and editing. - Didn t keep well. Can be easy to clean.

19 Formats forever Betacam SP - my favorite VHS - fun Betamax - work great 8, Hi8 and Digital 8 - too many of them D1, D2 - new broadcast standards Digital Betacam - introduces SDI DVCam - ProSumer favourite Mini-DV - the absolute worst HDV - worse than Mini-DV HDCam - introduces HDSDI. Not widely accepted, really expensive Issues with Tape Playback SSS - Sticky Shed Syndrome So common It s your worst enemy The tape has likely absorbed moisture from the air and emulsion has gotten soggy. It will come off during playback and clog the heads. Even tiny particles can interfere with playback Humidity, humidity, humidity Proper storage is critical LOL - Loss of Lubricant White Residue Can cause a squealing sound During playback lubricant is squeezed to the surface and should return back to the reservoir. Tape Damage - not much you can do about it Winding Defects - wrinkles cause improper contact with heads Country Laning - can be from manufacture, or a poor wind Edge Frilling - Improper storage

20 Mold and mildew Water damage Hardware Maintenance is the toughest part of the job Must be actively cleaning, testing and searching for replacements Cabling - interference from cables touching a charge Syncing - problems with TBC Here's where the stickiness comes from. The binder is the chemical compound that holds the oxide particles together and sticks them to the tape backing. Under humid conditions (which means anything but

21 controlled low-humidity storage), the polyurethane used in the binder has a tendency to absorb water. The water reacts with the urethane molecules, causing them to migrate to the surface of the tape where they gum up the tape path during playback. Short strings of urethane molecules are particulary prone to water absorption, while long strings make the coating mixture too viscous to produce good tape. Middle-length strings are the best, but the tape manufacturers didn't know this at the time, and didn't always know what they were getting. In the case of Ampex tape, tapes most likely at risk are 406 and 456 manufactured from approximately 1975 through During those years, Ampex tested the goop they got from their binder suppliers simply by measuring viscosity. Unfortunately, the long and short strings average out, viscosity-wise, to a viscosity about the same as the ideal medium strings, so some tape was inevitably manufactured with an overly great proportion of short urethane strings in the binder. In the worst cases, as little as 3 days' exposure to 70% relative humidity can cause a tape to become gummy, but typically, it takes 2 to 15 years under normal, people-friendly ambient conditions. In 1984, Ampex started doing it's incoming inspection with a high pressure gas chromatograph (that's when it was invented), and was able to more accurately determine the molecular makeup of its binder, and control production much more carefully. -Josepehson Engineering Inc Identifying Degradation - Base Film: Edge Damage, Stretching, Country Laning, Winding Defects - Mylar does not degrade under normal conditions - Mold growth - bacteria forms as white powder

22 - SSS - Sticky Shed Syndrome - Lubricant problems - Squealing (Stick Slip) - Flaking Sticky Shed Syndrome Binders will absorb water from the air and break down: The binder polymers used in magnetic tape constructions are subject to a chemical process known as hydrolysis. In this process, long molecules are broken apart by a reaction with water to produce shorter molecules. The shorter molecules do not impart the same degree of integrity to the binder system as do the longer molecules. As in a wool sweater, if enough individual yarns are cut, the sweater will eventually fall apart. -Van Bogart, CLIR Solutions Baking Store tape in an oven on, around 130 fahrenheit, for a few hours. Should re-bind the emulsion, allowing the binder to partially melt and adhere the metal particulate to the film. Damages emulsion. Makes it brittle and likely only good for an immediate transfer. Cleaning Pass the tape over a linen roller and allow the loose/wet emulsion to scrape off. DIY Cleaning Solutions Sounds dangerous. Not as bad as you think. RTI Tapechek

23 AV Artifacts Atlas Most Common Term: Drop-out A portion of signal is missing. Everything s a drop-out. Digitization Containers, Streams and CODECS A Container (often called format) holds the streams of data and XML header that make a digital media file. Streams of data are typically 1 video and 2 audio streams Common containers: AVI, MOV, MXF, MKV,.MP4 CODECS are compression and decompression algorithms Common Codecs: H.264, Uncompressed, Pro Res, DNxHD, DV Typically codecs are categorized by purpose: Capture: Uncompressed, DV, Motion JPEG Intermediate: Pro Res, DNxHD Access/Distribution: h.264, flv Samma Systems In use at the National Library and Archives Output format is JPEG2000

24 U of T Standard Audio: BWF - 96,000Hz, 24bit. 96,000 times per second you can record a binary number consisting of 24 bits. Capture: Quicktime.mov - 10 bit Uncompressed, 48kHz, 24bit Storage: AVI.avi - FFv1, 48kHz, 24bit Access: MP4.mp4 - h.264, AAC 128 kbit/s Storage - Digitized materials are stored on LTO Data Tape Uncompressed video is roughly 1 gigabyte per minute. - Lossless compression algorithms can compress video to ⅓ of the original size. FFMPEG - FFv1 - Open source compression algorithm. - Much better for software compression than JPEG Command line Linux tool - Must be compiled with a collection of codec libraries XML Metadata - Media files contain an XML header - Tools like MetaEdit and MediaInfo can view this data - Library of Congress AudioMD and VideoMD -

25 Data Tape - Widely used - Most effective storage means - Currently LTO-6. Holds 6.25 TB for about $50 per tape - Addresses backwards compatibility - Mark Pellegrino 2017 mark.pellegrino@utoronto.ca