Duncan Smith 2011-11-08 This is a utility intended to recover data from a standard four-track quarter-inch magnetic tape. The only modulation scheme supported is the 1600 bits per inch phase-encoded format used in tapes in the 1970s. In order to create a tape image to run this utility on, you must first digitize an existing tape. It is essential to digitize the tape at a sufficiently high sample rate. I suspect that four to six times the Nyquist limit is a reasonable target. 1,600 bpi tape has 3,200 flux transitions per inch; each flux transition is a half-cycle. Therefore, the Nyquist frequency for this tape format is 3,200 samples/inch. I have done this by removing the tape from the cartridge and running it through a benchtop tape transport, using a head from a spare tape drive. The playback heads were connected one at a time to a high-bandwidth audio recorder, and the tape was moved across the head at 15 inches per second. The nominal speed of this tape is 30 inches per second, and the sample rate used is 4*44100 samples/sec, or 176,400 samples/sec. This gives an effective sample rate of 352,800 samples/sec at nominal speed. Simple calculations show that this is 23520 samples/inch, or 14.7 samples per bit of recorded data. This is equivalent to 7.35 times the Nyquist frequency calculated above, and so should be more than enough sample bandwidth. Indeed, inspecting the resulting audio files in Audacity shows a good deal of waveform detail.