I use Audacity 2.0.0 on Ubuntu 12.04. I have about 4 years experience using sound editing software. All of a sudden opening any Audacity project or music file (usually mp3) I created or edited is full of red marks that signify a sample is too hot and will be clipped. This after painstakingly editing my projects over the years to normalize at 0. To my knowledge I have not changed any settings. Is there a setting that would have the effect of increasing the gain (I assume) on any track opened? It’s a hassle having to normalize everything to 0.0 again.
MP3 is an imprecise format. Unlike PCM formats (such as WAV), it does not save the value of every sample, rather it uses clever algorithms from which it can recreate, fairly accurately, the “sound”. Because it is imprecise, audio that is normalized to exactly 0 dB and then encoded as MP3 will usually show sample values slightly above 0 dB when it is decoded. Usually this is not a problem as it does not cause audible distortion, but if you would prefer to avoid this occurrence, then it is necessary to normalize a little below 0 dB before encode (about -2 dB will normally do), or, use a different file format such as WAV, FLAC or Ogg.
Ok, I understand and respect your answer for mp3 format. But what about the fact any project files (Audacity’s file format, not a codec format like mp3 or flac) are opening with values above 0 db? These project files were in good shape when I saved them and now they are full of hot samples and will all need to be re-worked. It is as though a default sound level has been increased and throwing everything off.
If you are using the usual default format of “32 bit float”, then “over 0 dB” is not in itself a problem, and 32 bit float format can handle values well above 0 dB. The only “problem” is that it will need to be amplified to a peak level of 0 dB or less before playing or exporting.
I don’t see how an Audacity project can change all on its own. Sample values are just numbers. A sample value at 0 dB is +/- 1.0000. A number stored on a hard drive will remain as that number until ether it is changed to a different value or the drive fails (data corruption).
The red “clip indicator” lines on the waveform do not mean that the audio IS clipped. They warn that the peak level is 0 dB or greater so it “may” be clipped. If an occasional sample is at exactly 0 dB (the sample has a numerical value of +/- 1.000) then that will not “clip” the audio, but will show a red clip warning line.
