Single Track, ½ Track, ¼ Track
A track is a portion of the magnetic tape that is recorded onto. A full track tape recorder uses the entire width of the tape to record one track onto. Early tape decks would use full track heads although for modern day purposes, a full track machine has limited use (and is hard to find).
A ½ track deck has two tracks, each which use one half of the tape width. Typically a ½ track deck would be used for pro or semi pro use, and the tape can only be used in one direction.
A ¼ track reel to reel is the most popular format for home stereo use. The tape heads are configured so that ¼ of the tape is used for the left and right channel, and are set so that you can flip the tape over, and record two more tracks using the remaining two ¼ tracks.
A 4 track recorder (also called 4 channel on occasion) will use ¼ of the tape width per 1 of 4 tracks, and has the ability to record all four tracks in one direction. Quadraphonic tapes from the 1970s use the full width of the tape, as do 4 channel tape recorders, typically used in home recording studios.
Multitrack machines will have up to 24 tracks, and up to 2” wide tape to record onto. Most of these machines are used in recording studios, although the boom in home recording studios had a number of companies produce decks that provided as many as 8 individual tracks on a 1/4 “ tape, and some semi pro recorders put 8 tracks on ½” tape.
Generally speaking, the more width of the tape that you use per track, the better quality recording you will get. All recording tape, especially low end brands or tape that has been played repetitively can suffer from uneven oxide on the tape surface. This can result in uneven sound levels, or dropouts, where the sound level drops for a fraction of a second due to a thin oxide layer. The wider the track on the tape, the less likely you are to hear tape flaws, as a dropout may only exist on a portion of the width of the tape, so a recorded track over a wide area of tape is less likely to produce audible tape dropouts or other flaws. Similarly, a tape recorded at a fast speed is less likely to produce audible tape flaws.
Crosstalk occurs when the sound recorded on one channel bleeds over to another channel. Ideally, what is recorded on one track of a tape will be played back only on that channel, but due to the way magnetized tape works. The tape head will pick up low level sounds from an adjacent channel. This can easily be heard by recording a bass heavy song on one side of a blank ¼ track reel to reel, then flipping the tape over, and playing back the second blank side of the tape. If the volume is turned up, you will most likely hear the muted bass notes or bass drum on what is supposed to be the blank side of the tape. The tape head is simply picking up a bit of bleed-over or crosstalk from the recording on the other side. This is simply the nature of tape. Recording studios use some tricks to reduce crosstalk, but they’re not really applicable to home stereo recorders. Note that while you can get cross-channel crosstalk on a ½ track tape, you won’t hear erroneous bass beats or notes from something recorded on the other side of the tape, since ½ track tape uses the whole tape in one direction. It’s another reason why higher end recordings are made on ½ track machines.