Quarter-inch formats and two-channel erase heads.
Click on the images to open a larger view in a new window. For details on the track width of the centre track timecode, please see the drawing on my Synchronization page.
Note: Audio tape is generally A wind (oxide facing the hub of the reel). The tape is recorded/played so earlier material is at the right (i.e., tape moves left to right). This view is THROUGH the tape looking at the heads, with the magnetic coating facing away from the viewer. Track numbering starts at the top, away from the deck plate for all common audio transports, such as the Ampex 350/440, Studer A807/A810/A820, and Sony APR-5000.
See also: equalization, noise reduction, reels & hubs, speeds, synchronization, tape timing, tape winding, and track configurations.
Quarter-inch tape was the mainstay of amateur recording from the early 1950s through the 1970s. Professionally, it was used from 1947 (and earlier in Germany) and continues into the 21st century. In general, it is robust, but some types of tapes have suffered from various adverse aging processes, some of which are discussed in the tape aging category. Useful information (some articles are in both categories) is also discussed in the storage-care-handling category.
Full track mono tapes are best reproduced with a full-track head. The early German tape is 6.5mm wide instead of 6.35mm. We have modified one set of tape guides to accommodate that width without binding. The 1960 Ampex paper (see below under 2-track) shows full-track width at 234 mils.
Mono 3M DynaTrack was proposed in a 1964 AES paper by Jack Mullin, n is explained briefly here. We do not believe any of these machines were ever made.
Two-track NAB mono and stereo tapes.This has been a long-term standard for radio and recording, but was only used widely in the 1950s for mono home recording. The above drawings show 75 mils for Ampex stereo and 82 mils for NAB stereo. This requires more explanation. In October 1960, several Ampex engineers (Mort Fujii, George Rehklay, John [Jay] McKnight, and William Miltenburg) publised in the Journal of the Audio Engineering Society “The Multichannel Recording for Mastering Purposes”. Figure 7 shows, among other things, half track mono with 82 mil track width and a 70 mil guard band and 2-track stereo with 75 mil tracks and an 84 mil guard band. The later NAB standard used 82 mils for both mono and stereo. It is my understanding that the narrower tracks were used to reduce crosstalk.
DIN Stereo is the format widely used in Europe for stereo master recordings. As is evident from the drawing at the top of the page, the tracks are wider, providing a better signal-to-noise ratio.
Quarter-track Stereo (and mono). This is perhaps the most widespread consumer format from the late 1950s through the 1970s. The above-referenced 1960 paper shows four 43 mil tracks with 25 mil guard bands, so this format was standardized by 1960.
Three-channel quarter-inch tapes were used in NAB cartridges and also in early, 1950s experimental 3-channel stereo. Three-channel recording was widely used in the 1950s on 1/2″ tape. Three channel on 1/4-inch tape is shown in the 1960 Ampex paper as 43 mil tracks with 57 mil guard bands.
Four-channel was used as a live recording format (two stereo pairs), for quadraphonic use, and also in some cartridges.
Four-channel was also used for instrumentation recording (click here). It is important to note that the track order between a 4-channel 1/4-inch audio tape and a 4-channel 1/4-inch instrumentation tape will normally be reveresed due to the way the track numbers are specified.
8-track, four channel is used for transferring 8-track cartridges. With our custom-built elevator head assembly, we can access any 0.021″ track or portion of a track on a tape which might help in recovering tapes that were recorded improperly or partially erased.
8-track, eight channel is a later, limited-budget music recording format.