Some excerpts from a Q&A with Award-winning Recording, Mastering and Restoration Engineer Steve Hoffman.
Link to all questions:
http://www.stevehoffman.info/faq.html
Q: So why didn't the record companies use these master tapes to begin with?
A: In the old days, you couldn’t just cut a record from the master tape or the stylus would just jump right off the record when you tried to play it. So in the old days, mastering was cutting a record so you could play it on an average phonograph. Unlike the CD’s of today with wide dynamic range (difference between the softest and loudest volume), the LPs had a much smaller range so you had to use a compressor to limit that range to an acceptable level. Also you couldn’t load up the bass too much or the stylus would jump off of the record. So you had to use an equalizer to back off on the low end or turn up the high end and you had to ride the levels so it didn’t get too loud. You essentially did what you needed to in order to have the best sound that would fit into the grooves of the record. And that being a very subjective thing - every mastering engineer had their own way of achieving that. In addition, while they were playing the master tape onto a record lacquer for use in making vinyl records, a tape was running to capture this version of the album. That became the EQ Dub or Cutting Master and was then sometimes incorrectly labeled the Master Tape and they put the real master tape away since it didn’t need to be used. So then any time another lacquer needed to be cut, you just pulled out the "LP master" tape. And depending on how long ago the recording was made, there might be a different tape marked master made for reel to reel duping or 8-track tape duping and that led to a lot of confusion when asking for the Master Tape.
Q: What's this about "baking" master tapes so you can use them?
A: Believe it or not, the tape manufacturers used to lubricate their tapes with whale oil. That natural lubricant worked so well that you can pull out a tape from 1949 and it will still play and it's wonderful. After the energy crisis in 1974, the tape manufacturers said they could make a synthetic lubricant that would work just as well. And that is what they did. And every tape from 1974 to around 1986 is made with that synthetic lubricant which starts to break down after about five years and then you can't play the tapes any more. Now they didn't know that was going to happen, of course, but that is what happened. So at first they tried to re-lubricate the tapes, which without it is like trying to rub sand paper on a fragile surface without any lubrication - and it didn't work. So rather than destroy all of these tapes, Ampex Corporation discovered that if you heat up the tapes in a convex oven to a certain temperature, then they will be playable for a short period of time. The other good thing they discovered was that you can heat them again every time you need to play them. I don't like to think about doing that, although I have had to before, but it's good to know that you can do that or you might as well throw the tapes in the trash. And our entire musical heritage from about 1974 to 1986 is plagued with this problem. What’s amazing is that the early stuff, recorded on cheaper tapes - that stuff works great still.
