Glossary

What is true peak, and why −1 dB?

True peak is the highest level your audio will actually reach once it is converted back to sound — including peaks that appear between the digital samples. Leaving 1 dB of headroom (a −1 dBTP ceiling) stops those hidden peaks from distorting when a platform re-encodes your file to MP3 or AAC.

A waveform that touches the ceiling gets flattened tops and distorts once a platform re-encodes it, because peaks appear between the digital samples. Leaving 1 dB of headroom gives those peaks somewhere to go. — With no headroom, the encoder's own peaks clip. −1 dBTP is the insurance.

This is why a file that looked fine in your editor can come back crunchy from a streaming platform: the encoder introduced peaks that were not in your version. The headroom is insurance against that.

Every platform preset in Cast targets −1 dBTP. The one exception is Master, which applies no processing at all — true peak included — because someone else is going to master it.