this is readtape version 3.10, compiled on Jan 9 2020 16:43:08, running on Thu Nov 4 22:30:07 2021 executable file: C:\data\projects\magtape_reader\bin\readtape.exe command line: readtape -tbin -deskew -m -textfile -bcd -tap pdp1_tape2 current directory: C:\Temp no backup\tape drives\data\7trk\MIT_PDP1 this is a little-endian computer For more information, see https://github.com/LenShustek/readtape reading file "pdp1_tape2.tbin" the output files will be "pdp1_tape2.xxx" .tbin file header: using .tbin ntrks = 7 using .tbin mode = NRZI converted on: Thu Nov 4 22:23:20 2021 max voltage: 7.1V time between samples: 1.280 usec no .parms file was found, so we're using these internal defaults for the NRZI parameter sets: parms active, clk_window, clk_alpha, agc_window, agc_alpha, min_peak, pulse_adj,pkww_bitfrac, pkww_rise, midbit, id { 1, 0, 0.200, 0, 0.300, 1.000, 0.300, 0.700, 0.200, 0.500, PRM} { 1, 0, 0.300, 0, 0.300, 1.000, 0.400, 0.600, 0.200, 0.500, PRM} { 1, 2, 0.000, 0, 0.300, 1.000, 0.400, 0.700, 0.200, 0.500, PRM} { 1, 0, 0.600, 0, 0.300, 1.000, 0.400, 0.600, 0.200, 0.500, PRM} { 1, 2, 0.000, 1, 0.000, 0.500, 0.500, 0.900, 0.050, 0.500, PRM} { 1, 0, 0.200, 1, 0.000, 1.000, 0.500, 0.700, 0.050, 0.500, PRM} { 1, 2, 0.000, 1, 0.000, 0.500, 0.500, 0.700, 0.050, 0.500, PRM} { 1, 0, 0.600, 1, 0.000, 0.500, 0.500, 0.600, 0.050, 0.500, PRM} compile-time decoding constants: peak height closeness threshold: 0.005V nominal peak height for rise calculation: 2.0V AGC maximum: 2 execution-time configuration: 7 track NRZI encoding, odd parity, 0 BPI at 50 IPS first sample is at time 0.0000000 seconds on the tape sampling rate is 781,250 Hz (1.28 usec) peak detection window width is 8 samples (10.24 usec) input data order: 0(msb)12345(lsb)p density was set to 800 BPI (25.00 usec/bit) after reading the first 1 blocks and seeing 10,002 transitions in 38 bins that imply 825 BPI starting preprocessing to determine head skew... head skew compensation after reading the first 8 blocks: track 0 delayed by 0 clocks (0.00 usec) based on 681 observed flux transitions track 1 delayed by 0 clocks (0.00 usec) based on 1117 observed flux transitions track 2 delayed by 0 clocks (0.00 usec) based on 970 observed flux transitions track 3 delayed by 0 clocks (0.00 usec) based on 839 observed flux transitions track 4 delayed by 1 clocks (1.28 usec) based on 1130 observed flux transitions track 5 delayed by 1 clocks (1.28 usec) based on 1317 observed flux transitions track 6 delayed by 0 clocks (0.00 usec) based on 1591 observed flux transitions the earliest peak is 23.52 usec, and the latest peak is 24.92 usec that peak difference of 1.39 usec, and the largest standard deviation of 1.93 usec, are 5.6% and 7.7% of the nominal bit spacing created statistics file "pdp1_tape2.peakstats_deskew.csv" from 7,645 measurements of flux transition positions to graph it from Excel, open the CSV file, then: insert chart 2D line creating file "pdp1_tape2.tap" creating file "pdp1_tape2.BCD.txt" wrote block 9, 596 bytes, 8 tries, parmset 5, AGC 0.59-1.39, 267 errs: 266 parity, LRC, avg speed 50.32 IPS at time 2.7509696, tap offset 49224 wrote block 10, 5512 bytes, 8 tries, parmset 4, AGC 0.62-1.59, 1 err: LRC, avg speed 50.67 IPS at time 2.8873446, tap offset 49828 wrote block 25, 6124 bytes, 8 tries, parmset 4, AGC 0.61-1.63, 1 err: LRC, avg speed 50.81 IPS at time 5.4288371, tap offset 141476 wrote block 43, 9 bytes, 8 tries, parmset 0, max AGC 1.00, 6 errs: 5 parity, LRC, avg speed 40.74 IPS at time 8.3218368, tap offset 252193 wrote block 44, 21 bytes, 8 tries, parmset 0, max AGC 1.00, 10 errs: 9 parity, LRC, avg speed 45.06 IPS at time 8.3227661, tap offset 252211 wrote block 45, 6060 bytes, 8 tries, parmset 4, AGC 0.63-1.78, 1 err: LRC, avg speed 50.82 IPS at time 8.4722150, tap offset 252240 wrote block 47, 6124 bytes, 8 tries, parmset 4, AGC 0.73-2.00, 1 err: LRC, avg speed 50.81 IPS at time 8.8102566, tap offset 264460 wrote block 52, 6122 bytes, 8 tries, parmset 6, AGC 0.73-1.93, 1 err: LRC, avg speed 50.86 IPS at time 9.6547802, tap offset 295200 wrote block 53, 20 bytes, 8 tries, parmset 0, max AGC 1.00, 10 errs: 9 parity, LRC, avg speed 45.86 IPS at time 9.6753728, tap offset 301330 wrote block 54, 5996 bytes, 8 tries, parmset 4, AGC 0.56-1.48, 1 err: LRC, avg speed 50.83 IPS at time 9.8237901, tap offset 301358 wrote block 56, 43 bytes, 8 tries, parmset 1, AGC 0.97-1.03, 21 errs: 20 parity, LRC, avg speed 47.95 IPS at time 10.0121638, tap offset 313515 wrote block 57, 6064 bytes, 8 tries, parmset 4, AGC 0.47-1.30, 1 err: LRC, avg speed 50.92 IPS at time 10.1614182, tap offset 313566 wrote block 59, 79 bytes, 8 tries, parmset 5, AGC 0.90-1.76, 43 errs: 42 parity, LRC, avg speed 49.71 IPS at time 10.3505715, tap offset 325791 wrote block 60, 6031 bytes, 8 tries, parmset 4, AGC 0.57-1.59, 1 err: LRC, avg speed 50.86 IPS at time 10.4991808, tap offset 325879 wrote block 64, 6120 bytes, 8 tries, parmset 4, AGC 0.68-1.84, 1 err: LRC, avg speed 50.88 IPS at time 11.1747302, tap offset 350374 wrote block 68, 6144 bytes, 8 tries, parmset 4, AGC 0.53-1.52, 2 errs: 1 parity, LRC, avg speed 50.89 IPS at time 11.8502502, tap offset 374958 wrote block 69, 6144 bytes, 8 tries, parmset 4, AGC 0.57-1.60, 4 errs: 3 parity, LRC, avg speed 50.89 IPS at time 12.0190989, tap offset 381110 wrote block 71, 6144 bytes, 8 tries, parmset 4, AGC 0.68-1.90, 2 errs: 1 parity, LRC, avg speed 50.88 IPS at time 12.3566426, tap offset 393414 wrote block 73, 6144 bytes, 8 tries, parmset 4, AGC 0.69-1.91, 2 errs: 1 parity, LRC, avg speed 50.90 IPS at time 12.6944320, tap offset 405718 wrote block 74, 6144 bytes, 8 tries, parmset 4, AGC 0.51-1.47, 4 errs: 4 parity, avg speed 50.85 IPS at time 12.8633626, tap offset 411870 wrote block 75, 17 bytes, 8 tries, parmset 0, max AGC 1.00, 1 err: LRC, avg speed 44.97 IPS at time 12.8816397, tap offset 418023 wrote block 76, 5582 bytes, 8 tries, parmset 4, AGC 0.61-1.74, 1 err: LRC, avg speed 50.83 IPS at time 13.0191885, tap offset 418048 wrote block 77, 511 bytes, 8 tries, parmset 4, AGC 0.66-1.80, 1 err: LRC, avg speed 50.96 IPS at time 13.0321190, tap offset 423639 wrote block 78, 6144 bytes, 8 tries, parmset 4, AGC 0.63-1.82, 2 errs: 1 parity, LRC, avg speed 50.95 IPS at time 13.2008026, tap offset 424158 wrote block 79, 6144 bytes, 8 tries, parmset 4, AGC 0.76-2.00, 2 errs: 1 parity, LRC, avg speed 50.91 IPS at time 13.3696742, tap offset 430310 wrote block 82, 764 bytes, 8 tries, parmset 5, AGC 0.53-1.12, 3 errs: 2 parity, LRC, avg speed 50.85 IPS at time 13.7446387, tap offset 448766 wrote block 83, 5339 bytes, 8 tries, parmset 4, AGC 0.43-1.21, 1 err: LRC, avg speed 50.85 IPS at time 13.8762752, tap offset 449539 tapemark at time 14.3076198, tap offset 467182 tapemark at time 27.2221210, tap offset 934738 tapemark at time 40.1335885, tap offset 1402294 tapemark at time 53.0437350, tap offset 1869850 tapemark at time 65.9519539, tap offset 2337406 tapemark at time 78.8662784, tap offset 2804962 tapemark at time 91.7780826, tap offset 3272518 tapemark at time 104.6866074, tap offset 3740074 tapemark at time 117.6053645, tap offset 4207630 tapemark at time 130.5140339, tap offset 4675186 tapemark at time 143.4258688, tap offset 5142742 tapemark at time 156.3479027, tap offset 5610298 tapemark at time 169.2486938, tap offset 6077854 tapemark at time 182.1592154, tap offset 6545372 tapemark at time 195.0648653, tap offset 7012928 tapemark at time 207.9518285, tap offset 7480484 tapemark at time 220.8514266, tap offset 7948040 tapemark at time 220.9448512, tap offset 7948044 pdp1_tape2.tap was closed at time 229.9354304 after 7,937,560 data bytes were extracted from 1301 blocks summary for file "pdp1_tape2.tbin": 171,696,401 samples were processed in 87 seconds (0.067 seconds/block) created 1 output file with a total of 7,948,052 bytes decoded 18 tape marks and 1301 blocks with 7,937,560 bytes from 228.41 seconds of tape data 27 blocks had errors, 0 had warnings, 0 had mismatched tracks, 0 had bits corrected, 0 had midbit timing errors 59 good blocks had to try more than one parmset parmset 0 was tried 1336 times and used 1237 times, or 92.6% parmset 1 was tried 89 times and used 1 times, or 1.1% parmset 2 was tried 88 times and used 0 times, or 0.0% parmset 3 was tried 88 times and used 0 times, or 0.0% parmset 4 was tried 88 times and used 76 times, or 86.4% parmset 5 was tried 28 times and used 3 times, or 10.7% parmset 6 was tried 28 times and used 2 times, or 7.1% parmset 7 was tried 27 times and used 0 times, or 0.0% created statistics file "pdp1_tape2.peakstats.csv" from 26,411,237 measurements of flux transition positions to graph it from Excel, open the CSV file, then: insert chart 2D line the earliest peak is 23.83 usec, and the latest peak is 24.91 usec that peak difference of 1.08 usec, and the largest standard deviation of 1.01 usec, are 4.3% and 4.0% of the nominal bit spacing deskewing with delays up to 5.6% of a bit time wasn't entirely effective the tape might have been written by two different drives if so you should consider separating the data into those sections