Occasionally we receive quarter-inch tapes that will be on small 3-inch spools. When reproduced on our capstan drive machines the result will have speed variation. They start off very fast then gradually slow down over the duration of the recording to around normal speed.
These reels usually have been recorded on rim drive machines. These types 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.
It’s not feasible or desirable for an audio restoration company to own unlimited machines of all types due to the time to service and repair them, find parts and storage space needed. 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 a digital solution is available at Creative Audio Works. This same process can be used to correct speed variations caused by recorders that used batteries that run low during the recording.