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Top Forums UNIX for Dummies Questions & Answers How to decrypt audio data from magnetic tapes? Post 302897696 by NICEPeppino on Tuesday 15th of April 2014 12:50:31 PM
Old 04-15-2014
Thank you Corona for your reply,

I have extracted some calls using the original software but it was a very long job. I cannot extract more than one call per time. Given the fact that the tape contains 10000 calls it is very slow.
The program I use is a proprietary backup tool, however, it uses common compression format: PCM and ADPCM. The tape stores calls grouped by recording channel. Each tape records 128 channels

Using the dd command I copied just 165 MB of data despite the fact the tape is 20 GB. Why? I think it is because it reads the first channel and than stops. 165Mb x 128 channels = (21120) the tape is dds4 20 gb so this should be the reason.
This is the command:

dd if=/dev/nst0 bs=32K of=output_file

How can I open the data extracted with the dd or other commands? If this info is not enough, what should I look at to decrypt the data?
 

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MT(1)							      General Commands Manual							     MT(1)

NAME
mt - magnetic tape manipulating program SYNOPSIS
mt [ -f tapename ] command [ count ] DESCRIPTION
Mt is used to give commands to a magnetic tape drive. If a tape name is not specified, the environment variable TAPE is used; if TAPE does not exist, mt uses the device /dev/rmt12. Note that tapename must reference a raw (not block) tape device. By default mt performs the requested operation once. Operations may be performed multiple times by specifying count. The available commands are listed below. Only as many characters as are required to uniquely identify a command need be specified. eof, weof Write count end-of-file marks at the current position on the tape. fsf Forward space count files. fsr Forward space count records. bsf Back space count files. bsr Back space count records. rewind Rewind the tape (Count is ignored). offline, rewoffl Rewind the tape and place the tape unit off-line (Count is ignored). status Print status information about the tape unit. cacheon Enable the readahead/writebehind cache on the tape unit. cacheoff Turn off the readahead/writebehind cache on the tape unit. Mt returns a 0 exit status when the operation(s) were successful, 1 if the command was unrecognized, and 2 if an operation failed. The cacheon and cacheoff commands currently only apply to the TMSCP driver and then only for certain drives such as the TU81+. No error is produced by the TMSCP driver if the cache commands are used. Other drivers will return an error code since they do not recognize the MTCACHE and MTNOCACHE functions codes. See mtio(4). FILES
/dev/rmt* Raw magnetic tape interface SEE ALSO
mtio(4), tmscp(4), dd(1), ioctl(2), environ(7) 4th Berkeley Distribution December 22, 1995 MT(1)
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