But maybe such "binarization" throws out information which might be useful? ZX Spectrum generates rectangular signal, after writing to tape and reading back, it

But maybe such "binarization" throws out information which might be useful? ZX Spectrum generates rectangular signal, after writing to tape and reading back, it becomes heavily low-pass filtered. So, I thought, if we take typical tape frequency response, pass ~1KHz and ~2KHz rectangle pulses through it, we get typical "0" and "1" signals as passed through tape, and if we cross-correlate them with tape signal, maybe we can achieve better results than by zero crossing detection? Also, what I felt unattractive in binarization/zero-crossing is that you should do band pass filtering anyways to fix DC offset and ripples that can affect zero crossings: https://imgur.com/ys78f1M https://imgur.com/ys78f1M. So, maybe if single filter is used for both frequencies of "marks" and "spaces", then we are doing it wrong and filters matched to marks and spaces could do it better? As alternative to filtering we can use adaptive binarization threshold and then morphology on binarized signal (AFAIK, this approach is popular in detecting various barcodes on photos).