What is True Peak?
Also called: dBTP, inter-sample peak
True peak is the highest level an audio signal reaches once it is converted back to a continuous waveform, including the peaks that fall between digital samples. It is measured in dBTP (decibels true peak).
A normal sample peak meter only reads the stored sample values. When the audio is played back or converted to a lossy format, the reconstructed waveform can swing higher than any single sample. These inter-sample peaks can go above 0 dBFS and distort, even though the sample meter never showed a clip.
True peak meters estimate those hidden peaks by oversampling the signal, as described in ITU-R BS.1770. Many streaming guidelines and distributors suggest keeping the true peak of a master at or below -1 dBTP, and a little lower for very loud masters, because encoding to MP3 or AAC can raise the peaks further.
Most mastering limiters offer a true peak mode that keeps the output under a chosen ceiling.
Example
A limiter set to a 0 dBFS sample ceiling can still produce true peaks above 0 dBTP once the file is played back or encoded. Switching the limiter to true peak mode with a -1 dBTP ceiling removes that risk.
Put it to work
Check the true peak and loudness of your master before you upload it.
LUFS Loudness Meter