Speeding up dd when converting tapes (EBCDIC->ACSII)

[equaad at dolphin.mit.edu]

I'm writing a program to help users easily convert their standard
EBCDIC IBM tapes to (2 Gigabyte) cartridge tapes on a SUN system. At
the moment I'm using dd with its various conversion options and it
seems to work okay, BUT, it's *very* slow (1.5 Meg/minute). Since
these people want to convert 5 or 6 200Meg tapes at a time, this is a
bit of a problem...

Does anyone know of a way to speed this up significantly?  I tried
messing around with the size of the conversion buffer (right now it's
the same as the blocksize of the input tape), but that didn't seem to
make any difference. Larger output recordlength and block size helped
some, but not a lot.

Is there a way to do the conversion in memory instead of on disk?
(actually, I'm assuming the conversion is not in memory by default, but
I don't know for sure). Any other way to speed up dd?

Perhaps there is an alternative program out there, or some other
better (faster) way to do this?

Thanks in advance for any help and/or advice!!! Please send e-mail, &
I can post results if there's interest.

-Ellen