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Reverse Engineering the Paper Jamz Pro instrument files

July 13, 2012
tags: reversing, paperjamz, bits, bytes, markov, audio

So, I'm working on a musical project, and I've decided to use only toy instruments. Specifically, the Paper Jamz Pro series of instruments from Wowwee. These are fun toys to play with, but what had me interested in them is the fact that they're customizable, to a certain extent.

There are 3 instruments in the Pro series line, of which I'm interested in two (guitar and drums). I was able to pick up mine relatively cheap as they're on clearance almost everywhere around where I live. Bonus. But, price aside, the reason I'm interested in these two instruments specifically is that using the free app from the Paper Jamz Pro website, you can change the voice of the instrument to one of a number of voices included with the app.

I've decided that I'll try to reverse engineer these instrument voice files, to see if I can manage to get my own samples onto these instruments.

Here's what I've gleaned so far. The instrument files for both guitar and drums seem to be structured similarly. There is a large header, which starts with a magic number (0xPJIG or 0xPJID) and several other bits of information that I cannot decode yet. Following that seems to be a series of audio frames. Using audacity's "import raw audio" feature, I've tinkered around and discovered that importing these instrument files as ADPCM VOX files at 22,050Hz, you get a decent sounding approximation of the sounds the instrument produces. However, the frames are filled with clicks, leading me to believe that there are interstitial headers throughout the file, perhaps between every frame, which hold metadata for the instrument to use.

Either way, it's been fun so far. Let's see what else I can figure out.

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