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[Creating TAP Files][Writing TAP Files]

Creating TAP Files

For now, this article won't go into deep details about the transferprocess, since this is documented other places. The reccomended way to transfer tapes is using a real C64 datasette. For PC-users, this is best done with mtap by Markus Brenner. You can download it at his site at
http://markus.brenner.de. Another pretty common way to transfer tapes, is through sampling it with a soundcard using a HiFi-tapedeck. DON'T DO IT!!!! It's a TERRIBLE way of dumping tapes, and the error-rate is VERY high. It's quite high even using a real datasette.

Okey, you got everything you need now (I assume that you've read the instructions found in the mtap-archive found at Markus Brenner's site), and if you follow these simple, but timeconsuming steps, you will soon be making the best TAP-files that can be made.

1. Dump the same title several times.

Yes, it IS timeconsuming, but it is the only way to make sure you get all datas pulled out from the tape. Often when reading these old treasures, a few pulses may be misread for different reasons. Especially on lower quality tapes. This is critical, because you may not always get any clues that the tape infact WAS misread. Even if some pulses are wrong, it may load and appear to be working. Some loaders has implemented checksums. A checksum is a value that is created by adding the read bytes into a sum. At the end of the file, the final sum is compared to the sum that is expected by the loader. These loaders aren't as demanding, but they're not 100% foolproof either.

The positive thing is that noisy, worn out tapes, USUALLY produces random errors. Using a TAP-scanner and cleaner (in this text, I'll be referring to my good friend Stewart Wilson's FinalTAP, since it's probably the best TAP-tool released at the time being), we can detect a lot of things. We can detect loadertype, if a checksum is present, and if it's OK. FinalTAP also creates crc32 values of the data. Both single files and the entire data. This is very useful since we then can compare different dumps of the same tape.

As a rule of thumb, you should have at least two identical dumps before you can assume the TAP is OK. I reccomend at least three dumps for loaders not containing their own checksum since they are more vulnerable. It's not likely that you have two identical TAPs which is faulty, but you can never be 100% sure. It's better to do one extra dump just to make sure the data is OK. If you can get the same title from several sources (assuming the other sources has the same version as you), that's even better. If two dumps from two different sources, even different sides of a tape turns out identical, you're 99,9% sure that your dump is completely errorfree.

Sometimes, the content from two different sources may vary slightly. This could be very confusing for the inexperienced, and also sometimes for the more experienced TAP-maker. That doesn't HAVE to mean it is an error (unless it fails to load, or an internal checksum indicates so). It's actually common with very small differences in "unused memory" in certain loaders (Novaload being an example of this). The software companies has written the game including random garbagebytes present in RAM at the time and those bytes may differ en two different recordings, even on the same tape. This is unfortunately something we cannot do anything about, but I would advise you to try locating the differences to see if it can be any harm. An article on this subject will come later.

2. Time to clean up the bastard!

Well, you have a functional tape? Congratulations. Now we want to clean it up. As we've mentioned, old tapes are noisy and needs to be freshened up a little. FinalTAP also has functions for that. Actually, that is FinalTAP's main purpose. By pressing the "optimize"-button, FinalTAP flattens out the signals of recognised files and removes any noise that it may detect. This has at least two advantages. You get files that are excellent as mastertapes for writing back to real tapes again (these tapes will actually turn out cleaner and nicer than the originals you have), and the files will compress much better, which is nice if you want to share your tapes on the net.

Due to the way FinalTAP works, it may happen that not all noise is being removed entirely. This is because it does NOT touch anything it doesn't recognise. This is your gurrantee that FinalTAP won't damage your TAP-image. In these cases, manual hex-editing is necessary if you want a perfect TAP. This is not reccomended for inexperienced TAP-makers, because you could end up damaging the TAP if you don't know exactly what you are doing. The leftovers from FinalTAP will not harm the tape in any way, and the tape should still load fine on a real C64.

You should be aware of the fact that FinalTAP does not support all the different loaders out there, and probably never will, but it supports all of the most common loaders. You should also make sure that 100% of the TAP is detected. In some cases where some noise hasn't been removed, it will say it detected 99% after optimizing/cleaning. An unprocessed TAP may have down to 97% detected (This is the lowest value I've found myself so far).

3. ALWAYS save ALL your raw dumps

This is very important, because you can always clean a TAP, but never go back IF the process went wrong. The raw files can also be useful for research and developing utilities for those into that.

I hope by writing this article I've managed to give you a clue on how to succeed in making the best possible TAP-files for the community. If there's something you feel is not answered here, or you need some other help, feel free to contact me at slc@c64.no.