What is the difference between 1/2 track tape and 1/2" tape?

Discussion in 'Tape' started by Shakedown, Jan 10, 2019.

  1. Shakedown

    Shakedown Active Member

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    Can anyone help me answer sort of a newbie question I have around this subject.

    Back in 2014 I purchased my first reel to reel deck, that supposedly plays both 2 track and 4 track tape. A Teac 7030GSL.

    I began asking around to those in the tape community, and became aware that there is a difference between tracks and inches which I was using interchangeably to describe 1/2" and 1/2 track tape.

    It is sort of a confusing terminology, because the terms are so close together. From what I read in my owners manual, the Teac 7030GSL is a 1/2 track machine.

    Does that mean it plays 1/2" tape or just 1/2 track 1/4" tape like many other consumer decks out in the market made by Teac and Akai?

    I had originally thought my deck plays both 1/4" and 1/2" tape.
     
    Last edited: Jan 10, 2019

     

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  2. 1tumbleweed

    1tumbleweed Kozmik Kowboy Subscriber

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    1/2 track describes the way the signal is recorded onto the tape. A 1/2 track machine records the signal on the entire width of the tape, regardless of its physical dimension - 1/4", 1/2", 1" or whatever.

    1/2" tape describes the physical width of the tape - half an inch. It has nothing to do with what is recorded on it.

    Confusing, I admit. There is no machine I'm aware of that will play both 1/2" and 1/4" tape.
     
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  3. maxhifi

    maxhifi AK Subscriber Subscriber

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    Absolutely true. To clarify a little bit:

    1/2" means the tape is 0,5" wide, 1/4" means the tape is 0.25" wide.

    Full track means the entire width of the tape is used for one mono channel. This is done only in very rare circumstances on very old machines.

    1/2 track means that each channel of recorded information occupies half of the tape width. This is also referred to as two track. It can refer to a stereo signal where the left channel uses half the tape, and the right channel uses the other track, or, it can be two mono tracks, where one is on one side of the tape, and when the tape is flipped, it plays the other track.

    1/4 track means each channel of recorded info occupies 1/4 of the tape width. This is also called four track. Usually, two tracks are used for the left and right channels in one direction, and the other two tracks are used for the left and right channels on the other direction. Most consumer 1/4" tapes and recorders are in this format. It can also be used for a quadrophonic program, where the four tracks are all used in one direction.

    8 track, 16 track, etc are studio formats, used for mulitrack recording. Here the tape is divided into 8 stripes, or 16, etc. each with its own track. Some machines (e.g. Tascam) were marketed at home studios can use this format.

    Note that a tape transport and heads cannot be multi-format. The rollers, transport mechanism, etc are all set up for a specific tape width, and the heads are built for the track width.
     
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  4. Shakedown

    Shakedown Active Member

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    Thanks folks, that clears up many things! So would that mean if my Teac is a 1/2 track machine, it cannot play 1/4 track tape?

    I wonder how that works because there is an option to playback 2 and 4 track, and all 4 track consumer tapes are 1/4 track.

    I guess the circuit board tell the 1/2 track heads to turn off during playback, and it looks like a hybrid design.

    https://www.hifiengine.com/manual_library/teac/a-7030gsl.shtml
     
    Last edited: Jan 10, 2019
  5. MaxxVolume

    MaxxVolume Addicted Member

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    Probably similar to my Pioneer 1020 decks, which have a 2-position switch....in the "2 ch" position, (for 1/4/track tapes), the playback head picks up the output from tracks 1 & 3 for Side One, and then tracks 2 & 4 when you flip the tape over for Side Two.
    When moved to the "4 ch" position, it picks up all 4 tracks of a Quad tape, which has all 4 tracks recorded in the same direction (there is no Side Two).
    This typically applies to playback only, recording still takes place in the normal 1/4 track mode.
    Your deck, being a 1/2 track, will record and play 2 tracks, one direction, or (probably) playback only in Quad.
     
  6. 1tumbleweed

    1tumbleweed Kozmik Kowboy Subscriber

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    That appears to be correct. The specs call for 2-track erase, record and play heads, and an additional 4-track playback head. So, the unit records and plays 1/2 track, but also will play back a 1/4 track tape.

    BTW, You can play a 1/2 track tape (with some loss of signal) on a 1/4 track machine, but not the other way around. I had quite a few early pre-recorded 1/2 track tapes which played adequately on my 1/4 track machines.
     

     

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  7. jlb2

    jlb2 Well-Known Member

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    Not simultaneously, but some machines can be converted. It requires changing the head block and a transport conversion kit including tape guides, rollers etc. JRF Magnetics offers this service: http://www.jrfmagnetics.com/index.html?JRF_mainframe=/halfinchprices.html

    This is mostly true for consumer machines. OTOH full-track has always been the only option for professional mono recording (radio and cinema). See Nagra, Stellavox and Studer, for instance, full-track mono machines have been available until they stopped making RTR recorders.
     
    Last edited: Jan 14, 2019 at 1:22 PM
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  8. kfalls

    kfalls Super Member

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    I've done the 1/4" to 1/2" conversion on our Studer A-80. John (JRF Magentics) can provide all you need including the heads. John is a great guy to work with.
     
  9. jlb2

    jlb2 Well-Known Member

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    As regards Shakedown's original question, the A7030GSL has two playback heads, one for 2-track and one for 4-track. The "2 track / 4 track" switch simply connects one or the other to the head preamplifier on the user's request, as explained in the service manual downloadable on hifiengine. Having two PB heads (or having two playback machines) is the only solution to play both 2-track and 4-track tapes for the following reasons:
    • Correctly playing a 2-track tape with 4-track head is not possible with the standard 2-track layout: the position of the left track is fine, but the right track doesn't completely overlap, hence a big level difference, causing the need for two different plaback heads. If the tape was recorded on a professional radio machine with the wide (2.75 mm per channel) 2-track layout, the space between tracks is narrower so things might be easier (but I've never tried it myself).
    • It is not possible to properly play a 4-track stereo tape with a 2-track head due to the simultaneous presence of two unrelated tracks on the same channel. It may be possible if the tape was recorded in only one direction, but with the right channel problem (partially overlapping track and PB head) and the extra problem that the head will pick up noise from the unrecorded width of the tape.
     
    Last edited: Jan 14, 2019 at 3:32 PM
  10. KentTeffeteller

    KentTeffeteller Gimpus Stereophilus!

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    It records and plays back 1/2 track Stereo. It uses 1/4" tape. 1/2" tape machines are not made by Teac, Akai, or other consumer companies (Teac's Tascam Series pre Tascam offered a 1/2" based machine or two, but those were aimed at home demo studios or recording studio use)
     
  11. 1tumbleweed

    1tumbleweed Kozmik Kowboy Subscriber

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    I must restate my position on this. I believe what you're saying is incorrect, because I've done it...many times. In my R2R days, I owned about a dozen or so early half-track stereo prerecorded tapes that I played quite often on my quarter track TEACs of various models. There was NO "big level difference".

    So, to summarize: I strongly disagree with "it's not possible", although I recognize your caveat of "correctly". Maybe I didn't feel the same level of incorrectness that you do.:idea:
     

     

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  12. Shakedown

    Shakedown Active Member

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    Great info on this thread!
     
  13. jlb2

    jlb2 Well-Known Member

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    Well, since track layouts are set by standards, it is easy to go past the "agree/disagree" point and put actual figures on the level differences I was talking about.

    A well-known good source for track widths is this page on the IASA web site, and I will refer to this page for figures and reference data.
    • Figure 2 shows that many standard layouts have existed for 2-track 1/4", so we'll concentrate of the one commonly used for consumer decks, including TEAC, namely NAB 1965: 6.3 mm total tape width, 2.1 mm channel width, 1.85 mm centre gap width. Taking the upper edge of the tape as zero, this means that the left channel extends between 0.125 and 2.225 mm, and that the right channel extends between 4.075 and 6.175 mm.
    • Figure 3 shows the layout for 4-track, which is the same for all the decks. The left channel extends from 0.025 to 1.025 mm and the right channel extends from 3.525 to 4.525 mm.
    From there, it is straightforward to determine the common part of both channels, and see that the left 2-track channel covers 90% of the 4-track playback head's channel ([1.025-0.125] mm out of [1.025-0.025] mm), ie. a 1dB level loss. OTOH the common part of the right channel only extends between 4.075 and 4.525, ie. 0.45 mm for a playback channel width of 1 mm. That's only 45% coverage, ie. a 7dB level loss. As a result, the right channel will be played at a level 6dB lower than the left channel - and it's what I consistently measure on my machines. This is a huge difference, and I don't know why you didn't notice it but it is definitely there.

    I can only suggest that you were somehow compensating the output levels, or just not paying attention, or those tapes were not really 2-track but 2-channel in a 4-track layout (I've noticed that, especially in the early days, the prerecorded tape manufacturers were not always crystal-clear in their technical explanations), or one of the machines was (possibly voluntarily) misadjusted in such a way that the 2-track recorded channels covered the 4-track playback head.

    Another possibility is that these 2-track tapes of yours were recorded on wide-track machines such as those used in broadcast radio: I've done the same calculations using Studer's data and the level imbalance is an unnoticeable 0.25dB in this case. Of course, this is a rare case, and even if you were so lucky to only have wide-track tapes, you shouldn't take this for granted. Well, anyway, the important point here is that the 4-track PB head of a Teac A-7030GSL cannot correctly play a tape recorded on a Teac A-7030GSL (or any other 2-track Teac) due to the track layouts - and Teac never claimed it could do it, they just said it was "a fourth 4-track playback head for playing back pre-recorded 4-track stereo tapes".

    Another thing to consider is that, even with a hypothetical 100% channel coverage, you would still be playing with a 1 mm wide head a signal that was recorded with a 2.1 mm wide head. By doing this you are losing 3dB in signal/noise ratio, so it still wouldn't be a very good way to play 2-track tapes.
     
    Last edited: Jan 16, 2019 at 4:00 PM
  14. phantomrebel

    phantomrebel Serial Tapist Subscriber

    What about the possibility of tumbleweed playing a 1/2 track stereo tape on a Teac Quad deck?
     
  15. 1tumbleweed

    1tumbleweed Kozmik Kowboy Subscriber

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    Nope. Had those 1/2 tracks long before quad was thought of. It was probably an A-1200. Or an old Roberts. Or an old Lafayette.

    Or any of the other R2Rs I had prior to 1970...:D
     
  16. Shakedown

    Shakedown Active Member

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    Too bad they don't make pro decks that playback both 1/2 track and 1/4 track tape.

    I have to consider the benefits of buying a dedicated 1/2 track machine. I was looking at MCI 2 track 1/4" machines, because most of the reels in my collection are 1/2 track.

    I also want to record to 1/2 track tape, but love my 1/4 track consumer music collection. It begs the question do I bother restoring my Vietnam era Teac deck that needs a decent amount of work, or just sell that and get a fairly newer Pioneer RT-909 and buy a dedicated professional 1/2 track machine for everything else.

    Oh what choices what choices!
     

     

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  17. jlb2

    jlb2 Well-Known Member

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    It's even worse than that: there has never been a pro 1/4 track deck - not one using 1/4" tape anyway. The track width was too narrow to offer a sufficient quality & reliability. I saw a heavily modified Nagra (or was it a Stellavox?) on ebay once, with the record head replaced by a makeshift 1/4 track playback head, and there was a switch to choose between heads. That really was a poor job, I've always wondered what could have justified inflicting this treatment to a perfectly good recorder.

    This said, if you really really want to use a pro deck to play both 2-track and 4-track tapes, you can try to find one with plug-in head block (many such models existed) and a spare block, and replace the play head of the latter. You would need to adjust the position (not just the height) and take into consideration the different electrical characteristics of the nonstandard 4-track head, but it's been done before (with a A80 if I remember well) so I know it can be done.

    But frankly, don't sweat it. A pro machine is cool and does bring a few advantages (accessible heads for cleaning & editing, better tension handling, more gentle tape transport for some models) but also hassles of their own: size & weight, cost and rarity of parts, standards that don't match consumer equipment, etc. It's not really worth it unless you do tape restoration for a living, and having two high-quality consumer decks, one for 2-track and one for 4-track is plenty cool too :thumbsup:

    My suggestion: Revox PR99 for 2-track (basically a B77 with accessible heads and balanced inputs/outputs - you can use the unbalanced Monitor output too so you're not loosing anything), plus a 4-track B77 or A77.

    EDIT: there was one exception after all, and I hadn't noticed it because it is a pretty rare machine around here, but many versions of the Otari 5050 have 2 playback heads, one for 2-track and one for 4-track.
     
    Last edited: Jan 18, 2019 at 6:56 AM

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