Audiovisual materials present all sorts of unique challenges to archivists. Regardless of the archival function, many of these challenges require access to information about measurements, recording and playback speeds, and other technical aspects of the audiovisual formats in question. You might have to calculate the playing time of a tape, or determine the length of the tape. Different formats and standards might require a measurement conversion.
Whatever the situation, you will likely find yourself looking for tools, guidelines, gauges, or calculators to help you along the way. Luckily, there are some really helpful resources out there.
Formats and Manufacturers
There have been many manufactures of audio tapes over the years and many more formats. AGFA BASF are the two largest manufacturers, but there are others. Some are now defunct (like IG Farben, the former parent company of AGFA and BASF), and some are still in business, but not producing magnetic tape (like 3M). Information about the various manufacturers and formats can help make decisions about preservation and create better descriptions of audiovisual materials.
- Richard Hess has a great set of information on magnetic, magneto-optical, mechanical, and optical media formats. Includes audio and audiovisual formats. Definitely browse through his site, there is a wealth of information.
- The Audio Engineering Society (AES) Historical Committee has a great list of AGFA, BASF, and IG Farben tape types (also available as an Excel Spreadsheet)
- The AES Historical Committee also compiled some resources about 3M audio tapes. These include:
- An introduction into 3M tapes
- A list of 3M audio open reel tapes in HTML format
- A list of 3M audio open reel tapes in Excel Spreadsheet format
- An index of the 3M “SoundTalk” bulletins (with full-text PDF scans)
- A scan of the splicing and recording tips inside the Scotch recording tape box, circa 1970
- A technical bulletin on print-through (the undesired low level transfer of magnetic fields from one layer of analog tape to another layer on the tape reel)
- Richard Hess has also compiled a useful set of notes on 1/4 inch reel tape, with links to people who can transfer each format described
Playback and Tape/Film Length Charts and Calculators
You will need different calculations for open reel audio vs film reels. I don’t have as much experience with film, so I’ll speak to open reel audio.
The running time of the audio recording is going to vary based upon the speed in which it was originally recorded (and will subsequently need to be played back). Speeds can vary from 1 7/8 inches per second (IPS) to 30 IPS (there are slower and faster possibilities, but this span will account for the most likely cases in an average collection).
The next variable will be the physical length of the tape itself. The thickness of the tape stock determines the length of tape that can be stored on a given reel. Standard audio reel sizes vary from 3 inches (diameter) to 10 inches (diameter). Some tape boxes stipulate the length of the tape, e.g. 1200 ft, etc. Some tape boxes stipulate the thickness of the tape, e.g. 1 mil. Depending upon the thickness of the tape and the size of the reel, you can determine the physical length of the tape in feet.
Then, knowing the speed the tape is recorded and the length of the tape on the reel, you can calculate the duration of the contents of the tape (Now, in the end you may find that the tape only contains a minute of actual audio content. The calculation only gives you a sense of the maximum amount of audio that may be stored on a given tape.). And, this assumes there is only one track recorded on the given tape in one direction. In some cases the tape is recorded in both directions (in which case the maximum duration would be doubled). In some cases there are four tracks. And on and on.
You’ll have similar issues with film, just different variables to calculate.
This Tape Timing Chart is approximate. Most reels will contain a bit more tape than indicated time implies, typically about 6%. The footage is actual.
These timings are for one program. There can be as many as four mono programs on one 1/4-inch tape.
It’s worth pointing out that this timing chart can be used in conjunction with the format lists produced by the AES Historical Committee. If you find the format on one of those lists, you can determine the tape thickness. Then with information about the amount of footage and the tape speed, you can estimate the playback time.
If you’re working with film, there are also a handful of web-based and downloadable calculators that can help you estimate playback speed and film length. Here is a selection of film calculators:
- Kodak Film Calculator. If you know the film format, frame rate, and film length, you can calculate the running time. If you know the format, running time, and frame rate, you can calculate the film length.
- Film Length From Weight and Size of Reel. Brian Pritchard has created an Excel Spreadsheet that lets you estimate the film length based on the weight and diameter of the reel.
- Running Time Calculator. Brian also created an Excel Spreadsheet that lets you determine the running time of 35mm, 28mm, 16mm, 9.5mm, Super 8mm, and Standard 8mm film based on the film length and frame rate.
- Film Footage and Running Time Calculator. SceneSavers created this calculator to estimate running time and length of film. The calculator works with any frame rate and can be used for Super 8, 16mm, 35mm, 35mm 3-perf, and 65 mm film.
There are some different consideration to make if you are working with digital audiovisual files. If you are working with audio, you will definitely want to consult the International Association of Sound and Audiovisual Archives‘ (IASA) Guidelines on the Production and Preservation of Digital Audio Objects. The Standard uses Open Archival Information System (OAIS) terminology and it has guidelines on everything from production and design to metadata and acquisition/ingest procedures to storage and access.
Determining the data rate, or the amount of hard disk storage space is often the biggest challenge, but there are some tools to help with that as well:
- Digital Audio File Sizes Table by Richard Hess. A nice table of uncompressed digital audio file sizes at various bit rates and sample depths.
- Audio Bit Rate and File Size Calculators by The Audio Archive. The first part of the calculator computes the bit rate for uncompressed audio (for example, WAVE or BWF file sizes). The second part computes the file size for a given bit rate.
- Data Rate Calculator by MPC. This is a great calculator! Use this data rate calculator to determine how much hard disk space you will need to store digital video. Enter the camera type, frame rate, and running time, and it will tell you how many frames there are and how much storage space you will need. Or you can enter the post-production file type (DPX 10bit, TIFF 16bit, TIFF 8bit, Apple ProRes 422 HQ, and Apple ProRes 422 SQ), frame rate, resolution, and running time, and determine how much storage space you will need. The calculator can also estimate the running time or length of 16mm, Super 8mm, 35mm 4-perf, 35mm 3-perf, and 35mm 2-perf film.
- Storage Calculator by Scene Savers. Use this storage calculator to estimate how much hard disc storage space you will need for your digital video files.
- Data Rate Calculator by AJA. Highly recommended! This is is a downloadable calculator. It can do calculations for video and audio files. Just a simple .exe file, but a nice interface and lots of options:
When the topic of calculating film length came up on the A&A list, a handful of suggestions for tools and supplies were made. They include:
- 2000′ Film Measuring Stick from Christies. For $39, you can get a measuring stick that fastens to the centre of a reel and provides measurements for up to 2000′ of film. Works with 2 and 3 inch cores.
- 3000′ Film Measuring Stick from Stanley Productions. For 48 pounds, you can get a similar measuring stick, that can measure up to 3000′ feet of film. Also works with 2 and 3 inch cores.
Preservation and Storage
There is a vast amount of information about preserving audiovisual materials out there. This is just a small sample of well-thumbed online resources.
- The Care and Handling of Recorded Sound Materials by Gilles St-Laurent for Conservation Online. A great introduction to how audio recordings are made and how they should be handled.
- Audio Preservation Subject Guide at University of Washington. This guide provides links to some great resources for audio preservation, most of which are freely available online resources.
- Tape Degradation Factors and Challenges in Predicting Tape Life by Richard Hess. This paper is chalk-full of information. From the abstract: This article “defines the basic tape types and the current state of knowledge of their degradation mechanisms. Conflicting prior work is reviewed and correlated with current experience. A new playback method for squealing tapes is described. The challenges in predicting future tape life is discussed. Illustrations of various types of tape degradations and a survey of many of the techniques used for tape restoration are included.”
- Again, the IASA’s Guidelines for the Production and Preservation of Digital Audio Objects is a must-use resource if you are working with digital audio files.
- Audio Preservation and Restoration Directory. If you need external services for your audio materials, the Association of Recorded Sound Collections (ARSC) has compiled this directory of preservation transfer, restoration, disaster recovery, equipment and supplies, and consulting and training services. Note that many service providers work with audio and audiovisual materials.
- Finally, Scene Savers created this Shelf Space Calculator. Use it to determine how much shelf space will be need to store various film formats.
This is just a small sample of online resources for audiovisual archivists. If you have a favourite link or resource you use that I overlooked, please feel free to send it along!