Intersample Peak
Definition
An intersample peak (ISP) occurs when the reconstructed analog waveform between two digital samples exceeds the level of either individual sample, potentially surpassing 0 dBFS. This happens because digital-to-analog conversion reconstructs a continuous waveform from discrete samples, and the peak of that continuous waveform may be higher than any measured sample value.
Context
Intersample peaks are a critical concern in mastering because they can cause audible distortion during:
- Lossy codec conversion (AAC, MP3, Ogg Vorbis) — streaming platforms re-encode masters, and ISPs can clip during this process
- D/A conversion — the converter’s analog headroom determines whether ISPs cause audible distortion; AKM converter chips have approximately +2.5 dB of headroom above full-scale, while ESS chips have significantly less
The standard mitigation is true peak limiting — setting the limiter ceiling to -1.0 dBTP (decibels True Peak) or lower. True peak metering oversamples the signal to detect peaks between samples, unlike standard sample peak metering which only measures the actual sample values.
Rollmottle (2022-05-13) — mastering-talk — 8 reactions
“Theoretically the lower the ceiling, the less risk there is of intersample peaks happening upon conversion to MP3 or some other format streamers use.”