the difference between 'dd' and analog tape copy is a regeneration of the write signal. In 'dd', the buffered data are written "freshly" from a GPIO into the c

the difference between 'dd' and analog tape copy is a regeneration of the write signal. In 'dd', the buffered data are written "freshly" from a GPIO into the cassette port. This results in a "stiff" or nearly perfect transition from '0' to '1' (and vice versa) because the output transistors in the chip are able to drive sufficient current into the high-impedance input of the cassette recorder's write circuitry mostly an amplifier (with a 20kHz oscillator mixed, but that's a long story) and the circuitry is able to generate rapid flux transitions and the tape can receive them. The resulting bandwidth of the signal into the write circuitry is roughly 20kHz and the resulting flux transitions in the ferrite are "sharp", "tall", brief, critically-damped, and quickly stablize on the microsecond scale. When performing an analog copy, those some excellent flux transitions are degraded at least 3 key distortions: First, there is limited bandwidth in the read circuitry. This is roughly equivalent to several low-pass or smoothing filters with various attenuations and cutoffs. They result from the original design intent of the recorder for audio, series inductance of the read head, and imperfect corrections for the frequency response of the media (think RIAA record curve). Additional distortions arise from noise, such as thermal, Schott, EMF, etc. There is also wow and flutter from the imperfections of the tape drive resulting in jitter. When the resulting imperfect signal is then sent to the write input of the cassette recorder, the flux transitions on the media are not as ideal and crisp as when a GPIO pin creates them. In general there are no regeneration stages, except for the "comparator" or differentiator in the input stage of the GPIO which reads the tape and determines at each time interval if the freshly-read bit is to be interpreted as a 0 or 1. The flux transitions may still be reliably read, but not after several generations of this process, and it will depend on the general quality of the tape recorder's electronic and mechanical components, tape quality, etc.