I am digitizing about 40 tapes with programs for the ZX Spectrum. I am somewhat puzzled by the waveform after digitization. The signal of most cassettes is meander-shaped. One of the cassettes can be downloaded from DropBox.
Some cassettes have a sinusoidal signal. This is an example of a cassette with a bad record. This cassette has an unstable amplitude. This cassette can be downloaded from DropBox
Sometimes there are records with "dancing" short pulses.
Questions: 1. What shape should the pulses be for successfully decoding programs recorded on these tapes?
What programs can help in decoding or preparing audio files for processing?
Any hacks for successful processing of tapes.
P.S. After some experiments with adjusting the signal level and the tape recorder head, I came to the conclusion that this is important for some audio tapes. And returning to the topic - the waveform must be sinusoidal.
Demonstration of the same piece of tape as an example (this files can be downloaded from Dropbox.):
Before adjust the tape recorder head
...after adjust the tape recorder head