[Coco] Dorsett Educational Tapes
Melanie and John Mark Mobley
johnmarkmelanie at gmail.com
Sun Jul 24 22:26:48 EDT 2016
I have reviewed one of the Dorsett Educational tapes on Tomas Edison.
It should be a mono (not stereo) file. The data and the voice/audio is on
the same track. Apparently no special hardware was required to read this
file, when it was new. The program can use motor on/off and audio on/off to
prevent the data portion for playing out the speaker.
The XRoar emulator can load a digital audio file, such as a wave file.
The file has too much noise and/or too little signal strength.
I think the file uses Frequency-Shift Keying for modulation of the data. I
think the CoCo makes one sine wave cycle for each bit. I think the CoCo
hardware measures the time between zero-crossings in order to demodulate the
audio stream. Does this should correct?
If I could make a 7Hz band pass software digital filter for each of the
frequencies of interest then I could clean up the files.
Perhaps a software Schmitt trigger like comparator could be used to clean up
the zero crossing and make the files readable again. Any thoughts on these
-John Mark Mobley
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