[LAU] Intersample peaks - Was: Normalize to -1db peak

Fons Adriaensen fons at linuxaudio.org
Wed Apr 22 10:09:28 CEST 2020


On Tue, Apr 21, 2020 at 09:53:12AM -0700, Len Ovens wrote:

> Lots of stuff out there on this. I came across an article that proclaims:
> "This worst-case example occurs when the audio tone is 1/4 of the sample
> rate." That is for 48000SR a 12Khz peak. This seems unreasonable to me
> though the idea that at 12Khz the peak could be as much as +3dbfs makes more
> sense. It would seem to me that intersample peak posibility varies with
> frequency and that the worst case would be 1/2 SR where the peak could be
> infinite (in which case it would be rendered as 0). However, if everything
> above 20k is filtered, that worst case is removed.

In theory there is no limit. It is possible (and quite easy) to create
a signal that produces *any* value of inter-sample peak you desire
(assuming 'perfect' D/A conversion or upsampling).

In practice (real world music signals), inter-sample peaks up to around
0.5 dB are observed. 

The EBU R128 meter specs require a peak warning at -1 dB FS.


Ciao,

-- 
FA



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