The famous DX7 synthesizer requires that all voice files are prefixed by a 6 integer, leading 0s, sequence number, for the files to be recognized. Scrounging around on the internet, one can find many DX7 voice-file collections. I now have 3500-odd such .syx files and since I don't want to be swapping DX7 cartridges around all the time, it is much more convenient to put all the files into one DX7 cartridge/directory, with all the voice files named according to the 6-digit uniquely-numbered prefix requirement. Here is how to apply a sequential, unique prefix to a bunch of files in a directory.
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