Two different peaks
- Sample peak (dBFS) is the highest sample value in the file.
- True peak (dBTP) is the highest point of the waveform the samples describe, including between samples, measured to ITU‑R BS.1770‑4.
When a loud master's samples sit close to full scale, the smooth waveform a converter rebuilds from them can overshoot between two samples. Those inter-sample peaks are invisible to a sample-peak meter.
Two real examples
Both are copies of our own 01 Low Orbit, as DropWave reads them:
| File | Sample peak | True peak |
|---|---|---|
| As mastered | −1.5 dBFS | −1.1 dBTP |
| 1.4 dB louder, no limiter | −0.1 dBFS | +0.3 dBTP |
| Pushed 7 dB into a limiter at −1 dB | −1.0 dBFS | +0.2 dBTP |
The second file looks safe on a sample-peak meter and goes over 0 dB when it's played. The third is the surprising one: the limiter held every sample at −1, and the sound still peaks above 0, because a limiter that watches samples doesn't see what happens between them.
Why it matters
- A converter rebuilding a waveform over 0 dB can clip.
- Encoding to AAC or MP3 changes the waveform and usually raises the peaks a little. The AAC version of the first file reads −1.0 dBTP against the WAV's −1.1.
- So delivery specs ask for headroom: −1 dBTP is the common ceiling for a streaming master.
How to check, and fix
DropWave reads the true peak of every file, says hot when it's close to 0 dBTP and clips above it, and checks it against your delivery spec. To fix an over: use a true-peak limiter with its ceiling at −1 dBTP, or bring the output down until it reads under.