[solved] Strange headroom at 0db: overshoot?


if I load an mp3 or whatever to a fresh renoise song with song settings “track headroom” set to 0db, the master output (at 0db) indicates overshoot over 0db, like 0.36db…

How is it possible, if a track logically cannot reach more than 0db? Did I miss something?

I guess: renoise is using floating point calculations for dsp before clipping to integer fixed point -1…0…1 as final result going to the sound card

How is it possible

In short: Resampling.

I would guess that the sample probably has Cubic or Sinc interpolation enabled, and that its sampling rate does not match the sampling rate of your audio playback/render (or that it’s being played back at a different pitch some other way)… and therefore resampling is taking place.

An unfortunate artifact of resampling and signal reconstruction in general, is that you may run into “inter-sample peaks”. Essentially, because the filter used to reconstruct the signal is based on some curve function, the reconstructed peaks may actually overshoot and exceed the amplitude of the surrounding samples which are perfectly fine. So if the sample itself is fully normalised to 0dB, then you can see how these inter-sample peaks can potentially exceed 0dB.

This was also problem on some older CD players with discs that had been normalised to 0dB, and cheap DAC’s were producing these horrible clipped peaks through your hifi.

You can read a bit about it here:

These days, I personally try to stay under -1dB on the master for this exact purpose. Some even suggest that you should keep it even lower, like -2dB, but I’d say that’s pretty extreme. Your mileage may vary :slight_smile:

Ok, thx for info. Ah yes, you told me this already before :slight_smile: And yes, I set it to sync / band limited.