Notes toward a history of interleaving

Elsewhere, I have described how interleaving in the CD system makes those marks corresponding to events which are contiguous in the real (i.e. the sound originating in the studio) discontiguous in the symbolic (i.e. the alternating pits and lands as they are demodulated by the CD player’s laser).1 The inverse process, de-interleaving, is applied during decoding and has the effect of making defects which are contiguous in the real (i.e. on the surface of the disc) discontiguous in the symbolic (i.e. the de-interleaved data before the crucial error-correcting step is applied). The closely related media-historical question, of course, follows: are there precedents for these processes?

As the reader familiar with its etymology will already suspect, some of the very first to “interleave” media did so by hand: the human compilers of valued or delicate codices. I will briefly consider further examples of interleaving in variety of other contexts. A basic form is shared by all these examples: two or more media are deliberately restructured, interrupting the structure of one medium by the intermittent interfiling of the components of another to create a new, blended medium that contains elements of two or more previously distinct media.2

  • The first use of “interleaving” recorded in the Oxford English Dictionary—the autobiography of Anthony Wood “antiquary of Oxford” (1668)—refers not to the interleaving of digital data, as described above, but to the insertion of free leaves between the bound leaves of a codex.3
  • The young male students addressed by J.S. Blackie’s vade mecum On Self Culture (1874) were encouraged to “interleave” blank pages into their most beloved texts, to facilitate careful note-taking and, ultimately, greater recall in their studies of these texts.4
  • Almanacs, a genre of print publication that began to appear in England during the sixteenth century, routinely contained blank pages facing the month-per-view calendars that typified them. As precursors to the now-familiar week-at-a-view diaries, “interleaved” almanacs with blank pages were occasionally advertised as such, and commanded a more-or-less onerous premium that depending on the cost of paper to the printer.5
  • Today, conservationists “interleave” non-reactive barrier paper between book leaves to prevent corrosion caused by the tendency of certain codices to deteriorate over time: their “inherent vice” that is caused by the chemical instability of the materials of which they are made. This practice is attested to by extant bound volumes from the 6th century BCE, in which interleaved parchment is used to protect more fragile papyrus pages, and may date back yet further.6
  • In high-voltage electrical engineering, so-called “interleaved” transformers use a wiring arrangement that was discovered and patented in the 1950s.7 If the windings in a transformer are taken out of their most natural sequence and self-interleaved, the transformer will leak less energy into the ambient electromagnetic field and be more resilient to sudden electrical impulses, such as those caused by lightning strikes.
  • The first recorded use of “interleaving” to refer to a fully automated process dates from 1956, relates to early digital electronic computing, and refers to the “interleaving of the digits of the words stored on the [computer’s magnetic] drum [memory]” for the purposes of computation.8 Interleaving data across the surface of the cylindrical drums used for short-term memory in early computers afforded greater flexibility in addressing and manipulating this data while the drum was in motion, and was also used until the 1990s in floppy disks and magnetic hard disc media.9 More recently in computing, the term interleaving is now primarily refers instead to strategies for scheduling computation tasks as they compete for the same computational resources.
  • When a new color TV standard was being designed in the United States in the 1950s, it was desired that any new format for the broadcast could be received and viewed by older, black-and-white–only television sets, a feature that became known as compatibility.10 The engineers who designed the new color television standard noticed the existence of the “gaps” in spectral space in the old signal into which could be “interleaved” additional information with which to colorize the monochrome signal, without sacrificing compatibility.11
  • In 2008 two educational psychologists investigating the effect of spaced repetition regimes on human subjects’ learning rate hypothesized that the juxtaposition of different class members, which was a side-effect of the spacing operation used in their study, that improved learner performance: not the fact of spacing itself.12 Subsequent research established that presenting learners contrasting examples in direct succession, which was referred to in the 2008 paper as the “interleaved” condition, improved induction.13

With this final example, we have come full circle: as with interleaved bibles and almanacs, the strategic resequencing of teaching materials today is similarly designed to mitigate the decay inherent in the recording medium that all of us carry about with us: memory. As seen above, the medium becomes more robust in some way as a result of interleaving: it might be more resilient to the failure of human or machine memory, or, more generally, might resist the corrosive effects of the passage of time, as the author of Self-Culture noted.14

Evidently, interleaving is not necessarily a “digital” technique, nor indeed it even always been figured as an autonomous, mechanical process. Like a kind of weaving, the construction of high-voltage transformers can be thought of as deploying interleaving as cultural technique, in so far interleaving exploits the close relationship between electricity, magnetism, and physical proximity to build more resistant apparatus. Notably, the interleaving scheme used in the CD system is designed to dovetail with the particular orderings of symbolic data that are most optimal for the subsequent error-correction and error-concealment circuitry. Since much the same could be said for each of these examples, taking them together, we might provisionally define interleaving as

a cultural technique that increases the resilience of technical media to degradation, by the strategic reordering of marks in a medium (support) according to a pre-defined scheme, which is generally designed to take advantage of distinctive features of that medium’s material extension.

  1. Eamonn Bell, “Interleaving as Cultural Technique in the Audio CD and the End of Archaeophonography,” Media Theory 5, no. 1 (2021): 115–46.↩︎

  2. In some cases, as is indeed the case with the CD standard, an original signal is being interleaved with itself, which I here call self-interleaving.↩︎

  3. “interleaving” n. OED online.↩︎

  4. John Stuart Blackie, On Self-Culture: Intellectual, Physical and Moral; A Vade Mecum for Young Men and Students, 4th edn. (Edinburgh: Edmonston and Douglas, 1874).↩︎

  5. Molly McCarthy, The Accidental Diarist: A History of the Daily Planner in America (Chicago; London: The University of Chicago Press, 2013), 49-50.↩︎

  6. John F. Dean, “World View of Book Conservation,” Collection Management 31, no. 1–2 (August 2007): 139–54, https://doi.org/10.1300/J105v31n01_10., 144.↩︎

  7. S. V. Kulkarni and S. A. Khaparde, Transformer Engineering: Design and Practice (CRC Press, 2004), 275–277; A. T. Chadwick et al., “Design of Power Transformers to Withstand Surges Due to Lightning, with Special Reference to a New Type of Winding,” Proceedings of the IEE - Part II: Power Engineering 97, no. 60 (December 1950): 737–44, https://doi.org/10.1049/pi-2.1950.0209.↩︎

  8. “interleaving” n. OED online.↩︎

  9. James Allen-Robertson, “The Materiality of Digital Media: The Hard Disk Drive, Phonograph, Magnetic Tape and Optical Media in Technical Close-Up,” New Media & Society 19, no. 3 (2017): 455–70, https://doi.org/10.1177/1461444815606368., 461.↩︎

  10. For background on compatibility in television standards in general and the NTSC standard in particular, see Jeffrey H. Rohlfs, Bandwagon Effects in High-Technology Industries (Cambridge, Mass: MIT Press, 2001), 137–165 esp. 142–145. See also, Jonathan Sterne and Dylan Mulvin, “The Low Acuity for Blue: Perceptual Technics and American Color Television,” Journal of Visual Culture 13, no. 2 (2014): 118–38, https://doi.org/10.1177/1470412914529110., 123–124.↩︎

  11. Milton S Kiver, Color Television Fundamentals (New-York; Toronto; London: McGraw-Hill Book Company, 1955), 20–21.↩︎

  12. Robert A. Bjork and Nate Kornell, “Learning Concepts and Categories: Is Spacing the ‘Enemy of Induction’?” Psychological Science, June, 2008, https://doi.org/10.1111/j.1467-9280.2008.02127.x. See also, an early use of the term “interleaving” in this sense in Doug Rohrer and Kelli Taylor, “The Shuffling of Mathematics Problems Improves Learning,” Instructional Science 35, no. 6 (November 2007): 481–98, https://doi.org/10.1007/s11251-007-9015-8.↩︎

  13. Sean H. K. Kang and Harold Pashler, “Learning Painting Styles: Spacing Is Advantageous When It Promotes Discriminative Contrast,” Applied Cognitive Psychology 26, no. 1 (2012): 97–103, https://doi.org/10.1002/acp.1801; Monica S. Birnbaum et al., “Why Interleaving Enhances Inductive Learning: The Roles of Discrimination and Retrieval,” Memory & Cognition 41, no. 3 (April 2013): 392–402, https://doi.org/10.3758/s13421-012-0272-7.↩︎

  14. Blackie, 21–22.↩︎