MAMEWorld Forums - Programming - Little app to decode triva tape data

Here's a little application I whipped up to process those .wav files mentioned in this thread:

http://www.mameworld.info/ubbthreads/sho...amp;o=&vc=1

Attached is a .zip file with the VB6 .exe and source code. You many need the VB6 runtime .dll, if you don't already have it, in order to run the .exe without compiling. (see if Google can help you find it).

This particular program isn't particularly user friendly, sort of a "first stab" at the problem.

Overview on how it works:

A valid .wav path/filename is entered into the upper left text box. Double-click the textbox to pre-process the file. A percent completed figure will appear on the title bar. It will take a few seconds to a couple of minutes depending on the length of the file.

The preprocessing upsamples the data (linear interpolation) by 4x. This makes it a little easier to deal with the jitter encountered in the main processing stage. The routine that does this is named "ovrSamp". It also converts 16 bit data to 8 bit data, if necessary.

Next, press the "see" button to see the beginning of the sample on a sample editor type layout. It, (and some of the other controls) can be pressed while the pre-processing is still occurring, but don't overdo it.

I didn't bother to make the graphics persistent on this app, so just click the "see" button to refresh the data view if it gets cleared by another overlapping app.

If things are working out, there should be a green squarewave appearing beneath the black sample wave. Click the mouse once on the vertical green line above the first number on the left under the green squarewave. A number will appear just to the right of the "sho" button in the middle.

Double click on this number and it will appear in the text box to the left of the "proc" button. Then press the "proc" button to process the file.

The process will take a few minutes. A percent complete figure will appear on the title bar of the app. When it is done, click the "sho" button.

The routine that does the dirty work is named "proc". Here is the core loop of it:

Code:


  For i = st To UBound(a)
    lb = b: b = a(i): If b >= 128 Then b = 255 Else b = 0 
    If (lb = 0) And (b = 255) Then   ' this detects zero crossings 
      lc = c: c = i - ld: ld = i     ' and measures how long ago the last one occurred
      If c < cu Then c = cn Else c = cm  ' this sets a threshold for hi/low periods
      If (lc <> c) And (Round(CSng(i - lld) / rate1) > 0) Then
        ch = "0": If c < cu Then ch = "1" ' this sets whether to record a mark/space
        res = res & String(Round(CSng(i - lld) / rate1), ch) ' adds string to result
        lld = i 
      End If
    End If
    If (i And 1023) = 0 Then Form1.Caption = Round(100# * i / UBound(a)): DoEvents
  Next

After pressing the "sho" button (it's a toggle), a text box appears with the binary data. Click the "frm10" button on the far right. The idea here is to delete the first few characters until the first three characters are "110", and then click the "frm10" button as needed while continuing to edit. Add or remove characters as needed to keep the "110" columns in line. If the recording was good, it should only take a few key edits to line things up. If you find a spot with 5 to 8 "1"s in a row, and the format is messed up at that point, add more "1" characters at that spot until the columns match up again.

Simplified example:

After double-checking everything lines up (and maybe selecting all and copying to the clipboard), press the "2nd" button to see the plaintext.

The routine that maps the binary to ascii is named "proc2". It decodes each binary pattern into a code number, and that number references a specific character in the ascii map (map reproduced from the 2513N spec. sheet).

If there is significant garbling, paste the contents of the clipboard (if you saved to it) and check the columns again. If you didn't save, press the "proc" button again and wait for the binary data to be re-created.

What the rest of the controls do:
"<", and ">" move the viewing point of the sample up and down by the amount of the current width of the form. By default, just the green squarewave appears (to save time). To see the waveform automaticly, ensure the checkbox named "autosee" is checked.

To zoom in on the waveform, change the number in the first text box to the right of the "autosee" checkbox. Click he "see" button after changing the number. "16" means compress by 16 samples to one pixel. This number can be a fraction (like "2.333"), if desired.

The other buttons allow for some crude editing of the waveform. Only the in-memory waveform is edited, the file on the disk is not affected. To paste a burst of 4800 hz data, click somewhere on the form (around the middle, for example), then click a second time a short distance to the left. Then click the "48" button, then click the "see" button. The results should be obvious. To reset any modifications to the in-memory waveform, doubleclick the filename textbox to re-pre-process it (and wait for a few moments for it to finish, then press the "see" button again).

Most of the controls have tool-tip reminders for their functions.