dBTP (decibels True Peak) measures the real peak of the analog signal a DAC will reconstruct, not just the highest stored sample. Between two samples the smooth reconstructed waveform can overshoot the sample values, sometimes by 1-3 dB, so a file that reads -0.1 dBFS can still clip a converter or a lossy encoder downstream. Meters estimate this by oversampling (4x is typical) before measuring. This is why loudness specs set a true-peak ceiling — -1 dBTP for EBU R128, often -2 dBTP for lossy-codec delivery — leaving margin so inter-sample peaks and encoding overshoot never distort on the listener's hardware.
