ZX Spectrum tapes use a lead-in tone which the ROM code locks onto.

Random noise (and data! from a previous block) before that is ignored.

Zooming out, the format is:

  Lead-in (~4..5s usually), followed by a short header with program name & type of data that follows.
  A short pause.
  A shorter lead-in (~2s), followed by the data/program itself.

Most software uses several of such blocks. Eg. a short BASIC loader, followed by a loading screen, followed by a # of KB's machine code.

As far as audio tape storage goes, the ZX Spectrum system was fairly reliable & user-friendly.

That's ignoring headerless blocks, speedloaders, and the many copy-protection schemes...