Peak Value

[TJB]

I just completed narrating a chapter and when I did my ACX check, everything was OK except for the Peak Value which was a -3db. Is there some way to correct this without re-recording the chapter???

[DVDdoug]

Follow the Recommended Audiobook Mastering Process and you'll nail the levels every time!

except for the Peak Value which was a -3db

-3dB is the upper limit so it should be OK... Maybe there's a small rounding error or something. The recommended process limits peaks to -3.5dB so it gives you a little wiggle room and it allows for a slight change that might result from the MP3 compression.

[TJB]

Doug, I did the audio mastering process just as always but this time the peak failed ... ACX Check says it exceeds -3db and it gets rejected when I try to upload it to ACX. Soooooooo, short of re-recording it, is there anything I can do???

And just what does Peak mean???
Thanx, Tom

[kozikowski]

And just what does Peak mean???

See those little tips in the blue waves up and down.

TipsandPeaks.png (46.07 KiB) Viewed 142 times

Those are the peaks. That's different from the RMS or Loudness.

Those peaks are not allowed to get any louder than 70% on the left hand scale. You can drag the timeline taller to make it easier to see. If you're watching the bouncing sound meter, that will actually go to -3dB.

As DVDdoug above, the mastering tools shoot for -3.5dB to make sure you don't exceed the specification. MP3 exports do not exactly follow the show in Audacity.

Somebody else had this problem and I'm trying to remember what went wrong.

You are following the Audacity Audiobook Mastering Suite tools right? If you are, what you have is impossible.

https://wiki.audacityteam.org/wiki/Audiobook_Mastering

There's another layer to this, too. When you finish announcing, you Export a WAV (Microsoft) 16-bit sound file of the work. Errors and all. There should be no "go back and announce it again." Just open up the backup WAV file and take it from there. You should also have a WAV of the Edit Master. You can't "fix" the ACX MP3 submission. If you try, the quality will sink below the 192 they require.

I need to drop for a while.

Koz

[DVDdoug]

Somebody else had this problem and I'm trying to remember what went wrong.

I think it was the gain slider to the left of the waveform.
That should be set to 0dB (no change).

Doug, I did the audio mastering process just as always but this time the peak failed ... ACX Check says it exceeds -3db and it gets rejected when I try to upload it to ACX.

Try running the limiter again, and make sure the settings are correct. If you limit to -3.5dB the peaks should be -3.5dB or less (more negative) and you should NEVER hit -3dB. (But like I said, MP3 compression can change the peaks slightly.)

You should go back to your WAV or project file... You shouldn't be re-editing MP3. When you open an MP3 it gets decompressed and if you then re-export as MP3 you are going through another generation of lossy compression.

And just what does Peak mean???

It's the waveform peak amplitude converted to decibels where the 0dB reference is +/- 1.0 on the scale to to to the left of the waveform, or 100%. 0dB is the maximum so your peak and RMS (a kind of average) is normally negative. -3dB is about 75%. -6dB is 50%. -20dB is 10%. (It's a logarithmic calculation that you can look-up.) Bigger negative numbers are "quieter". The RMS dB level corresponds pretty-well to perceived loudness, whereas peaks do not.



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The digital 0dB reference is 0dBFS (decibels full scale) so that's essentially the digital maximum (the highest you can "count" with 16-bits, etc.). But Audacity uses floating-point numbers internally so there is essentially no upper or lower limit and Audacity can go "temporarily" over 0dB.

When you measure acoustic loudness in the air that's dB SPL (sound pressure level). In this case, 0dB is approximately the quietest sound you can hear and dB SPL levels are positive.

[TJB]

Doug, thanx ... I hit limiter again and that fixed the issue