this is readtape version 3.10, compiled on Jan 9 2020 16:43:08, running on Fri Nov 5 08:39:01 2021 executable file: C:\data\projects\magtape_reader\bin\readtape.exe command line: readtape -tbin -deskew -m -textfile -bcd -tap pdp1_tape1_try2 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_tape1_try2.tbin" the output files will be "pdp1_tape1_try2.xxx" .tbin file header: using .tbin ntrks = 7 using .tbin mode = NRZI converted on: Fri Nov 5 08:31:54 2021 max voltage: 6.7V 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 860 BPI starting preprocessing to determine head skew... head skew compensation after reading the first 1 blocks: track 0 delayed by 0 clocks (0.00 usec) based on 2622 observed flux transitions track 1 delayed by 0 clocks (0.00 usec) based on 2158 observed flux transitions track 2 delayed by 0 clocks (0.00 usec) based on 2109 observed flux transitions track 3 delayed by 0 clocks (0.00 usec) based on 2421 observed flux transitions track 4 delayed by 1 clocks (1.28 usec) based on 2425 observed flux transitions track 5 delayed by 1 clocks (1.28 usec) based on 2438 observed flux transitions track 6 delayed by 1 clocks (1.28 usec) based on 4944 observed flux transitions the earliest peak is 23.55 usec, and the latest peak is 25.17 usec that peak difference of 1.62 usec, and the largest standard deviation of 1.22 usec, are 6.5% and 4.9% of the nominal bit spacing created statistics file "pdp1_tape1_try2.peakstats_deskew.csv" from 19,117 measurements of flux transition positions to graph it from Excel, open the CSV file, then: insert chart 2D line creating file "pdp1_tape1_try2.tap" creating file "pdp1_tape1_try2.BCD.txt" tapemark at time 13.7631462, tap offset 467552 tapemark at time 26.6722931, tap offset 935108 tapemark at time 39.5804736, tap offset 1402664 tapemark at time 52.4815296, tap offset 1870220 tapemark at time 65.3746650, tap offset 2337776 tapemark at time 78.2715418, tap offset 2805332 tapemark at time 91.1696346, tap offset 3272888 tapemark at time 104.0659149, tap offset 3740444 tapemark at time 116.9708032, tap offset 4208000 tapemark at time 129.8629056, tap offset 4675556 tapemark at time 142.7466483, tap offset 5143112 tapemark at time 155.6372019, tap offset 5610668 tapemark at time 168.5115827, tap offset 6078224 tapemark at time 181.3901760, tap offset 6545780 tapemark at time 194.2706995, tap offset 7013336 tapemark at time 207.1277978, tap offset 7480892 tapemark at time 219.9857293, tap offset 7948448 tapemark at time 232.8608448, tap offset 8416004 tapemark at time 245.7070298, tap offset 8883560 tapemark at time 258.5589594, tap offset 9351116 tapemark at time 271.4322726, tap offset 9818672 tapemark at time 284.3032179, tap offset 10286228 tapemark at time 297.1497216, tap offset 10753784 tapemark at time 310.0023040, tap offset 11221340 tapemark at time 322.8784973, tap offset 11688896 tapemark at time 335.7708326, tap offset 12156452 tapemark at time 348.6354880, tap offset 12624008 tapemark at time 361.4967373, tap offset 13091564 tapemark at time 374.3548429, tap offset 13559120 wrote block 2215, 3923 bytes, 8 tries, parmset 0, AGC 0.91-2.00, 2 errs: 1 parity, LRC, avg speed 51.11 IPS at time 376.1513997, tap offset 13620653 wrote block 2216, 2182 bytes, 8 tries, parmset 1, AGC 0.53-1.10, 916 errs: 915 parity, LRC, avg speed 51.05 IPS at time 376.2057370, tap offset 13624584 tapemark at time 387.2326221, tap offset 14026646 tapemark at time 387.3258125, tap offset 14026650 pdp1_tape1_try2.tap was closed at time 390.5373274 after 14,008,281 data bytes were extracted from 2281 blocks summary for file "pdp1_tape1_try2.tbin": 305,107,575 samples were processed in 137 seconds (0.060 seconds/block) created 1 output file with a total of 14,026,658 bytes decoded 31 tape marks and 2281 blocks with 14,008,281 bytes from 389.53 seconds of tape data 2 blocks had errors, 0 had warnings, 0 had mismatched tracks, 0 had bits corrected, 0 had midbit timing errors 0 good blocks had to try more than one parmset parmset 0 was tried 2314 times and used 2311 times, or 99.9% parmset 1 was tried 3 times and used 1 times, or 33.3% parmset 2 was tried 2 times and used 0 times, or 0.0% parmset 3 was tried 2 times and used 0 times, or 0.0% parmset 4 was tried 2 times and used 0 times, or 0.0% parmset 5 was tried 2 times and used 0 times, or 0.0% parmset 6 was tried 2 times and used 0 times, or 0.0% parmset 7 was tried 2 times and used 0 times, or 0.0% created statistics file "pdp1_tape1_try2.peakstats.csv" from 47,317,189 measurements of flux transition positions to graph it from Excel, open the CSV file, then: insert chart 2D line the earliest peak is 23.50 usec, and the latest peak is 25.04 usec that peak difference of 1.54 usec, and the largest standard deviation of 0.91 usec, are 6.1% and 3.6% of the nominal bit spacing deskewing with delays up to 6.5% 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