An analog loop bin uses a long loop of either 1/2" wide or 1" wide loaded in a large bin located in the front of the duplicator. This loop master tape is loaded into the duplicator's bin from a traditional open-reel of tape, where the program material has been recorded to it using a studio-type multitrack tape recorder in real-time beforehand. The loop tape for cassette duplication has 4 tracks on the loop bin master tape, and for 8-tracks has all of the 8 tracks recorded in one direction. The loop-bin master tape is read by the duplicator at a very high speed. For cassettes, either 32, 64, 80, or 100 times the normal speed of playback of an audio cassette is used, and 10 or 20 times the normal speed of playback is used for 8-track duplication. While this loop is being played back, the audio signals for the A and B side are sent to a "slave" recorder or an audio bus that contains multiple "slaves". The "slave" records from the loop bin master tape the 4 tracks for both A and B sides to an open-faced "pancake" reel of raw 1/8" audio tape, or all 8 tape tracks to back-lubricated 1/4" audio tape also wound on a "pancake" reel, at the same high speed. After it is recorded, this pancake of tape is then loaded onto special machines called loaders. For cassettes, the loader has cassette shells containing only a leader called "C-0" cassettes that are loaded one at a time or into a hopper where the C-0s are fed automatically depending on the type of loader. The tape from the pancake is then spliced onto the C-0 cassette's leader and then wound into the cassette by the loader. For 8-tracks, the tape is wound from the slave recorder onto a device mounted on its side, called a "sidewinder", which holds several small reels, and extracts and winds the tape from the slave recorder onto each reel into an endless-loop configuration, where each full reel is then placed in an empty 8-track cartridge and spliced together, either by machine or by hand, with a foil splice that holds the loop together. The foil splice also serves to automatically engage an 8-track player to advance to the next program when played. The loop of tape in the duplicator's bin usually will have a segment of clear leader spliced in between the beginning and end of the tape loop. This clear leader splice is read by an optical sensor in the loop bin duplicator, which triggers a cue tone that is recorded to the reel of pancake tape. This cue tone is read by the loader, and engages it, for cassettes, to stop and cut the tape from the pancake and either splice it to the leader in the C-0 cassette shell, or for 8-tracks, to disengage winding to an internal cartridge reel on the "sidewinder" mechanism and then cut the tape, with the winding resuming to a new reel afterwards. In fact, part of this de-spooling tone can be heard at the leader splice or foil splice of some previously recorded audio cassettes and 8-tracks respectively, as a very low-frequency arpeggiated rumbling of about 20 Hertz, sounding similar to how "motorboating" sounds with a radio or audio amplifier affected by such, but as an actual higher-frequency tone when played back at a higher speed. In the XDR duplication process for audio cassettes, the loop bin duplicators use 1"-wide loop tape instead, yielding in a better quality duplication.
Digital loop bin duplicator
Digital loop bins were also introduced in the early 1990s. The early digital loop bins replaced the source tape with audio data stored on hard drives that was read and sent to digital-to-analog converters that were connected to the "slave" recorders, but they were prone to failure because of the amount of stress put on the hard disks. The hard disks were replaced by huge RAM buffers which eliminated the failures but added greatly to the expense of the equipment. Since a digital bin was capable of playback speeds of 256:1 or better, a single bin could perform as two by splitting the buffer between two different programs. A program could be loaded and looped for production while an additional program could be loaded into the buffer. A real-time monitoring system could play back the audio stored in either buffer to check for potential flaws in the audio while both programs were looping for production. Another difficulty to overcome was the means for loading a digital bin. A bin could be loaded manually by recording directly into the bin's buffer, or it could be loaded by a high speed data device. At the time digital bins were first put into production, an S-VHS based storage device manufactured by Honeywell called a VLDS was used. A single S-VHS tape was capable of storing over 5 GB of data. These extremely expensive storage devices were eventually replaced by CD loading. The benefits of using a digital loop bin are:
There is no master tape to degrade during the copying process
Only a single master has to be made
Audio can be transferred at a much higher rate
The audio being reproduced can be monitored during production without shutting down the bin
