The capstan drive tape recorder is (or was) very common and was used in a huge range of cassette tape audio, video and open reel machines from cheap domestic to very expensive broadcast tape machines.
Occasionally we receive quarter inch tapes, always on small 3 inch spools, that reproduce on our capstan drive machines with terrible speed variation. They start off very fast then gradually slow down over the duration of the recording to around normal speed.
These reels must have been recorded on rim drive machines. These type of open reel tape recorders didn’t use a capstan and pinch roller to save space and more often cost. As there is no capstan, as the supply reel gets smaller the tape recording speed increases. When replayed on a rim drive machine the speed, while not likely to be ‘Studer stable’ will be pretty stable and the recording sound OK.
It’s not feasible or desirable for us to own unlimited machines of all types due to the time to service and repair them, find parts and storage space therefore we use a small range of carefully picked high quality tape machines that with care can replay most tapes, speeds and track formats. This is the problem with rim drive recordings and an analogue or digital solution must be found.
The tapes we received were 15 reels of family recordings from the Welsh Valleys. Others apparently had tried to transfer these tapes but gave up finding no material. This was easily solved as the tapes were wound the opposite way to normal so the oxide was facing out not in. This is the same as in audio cassettes. The original tape machine must have had its heads in a similar position to a cassette machine.
Rim drive tapes can be transferred to digital via conventional capstan drive machines at 3.75 ips. Then, using the non-linear speed change feature in the Diamond Cut DC8 software, one can “straighten – out” the speed variance so that it become constant. The software pvovides a graphical method for settup up the speed correction profile.
Craig / Diamond Cut Productions, Inc.