0 dB Peaks and ABXing 2017-11-06 11:56:33 To make this short, I'll start with the question, and then I'll post the story behind it.How do the different codecs (Opus, AAC, MP3) handle encoding/decoding when the original source (FLAC) peaks all the way to 0 dB? In other words, What happens when the decode algorithm results in sections louder than 0dB. Is there a recommended normalization for source files, so that the peaks are a certain dB difference below 0 dB?My guess there's some sort of on the fly normalization, or volume reduction. So that the sound doesn't "clip" ? But it seems to work more like a loudness filter than a normalization of the whole file?What happened was that I was ABXing FLAC vs 32kbps OPUS, and I found a section of the song that was easier to ABX because of a volume difference. The section on the source was louder and peaked to 0 dB considerably more than other sections. When decoded, foobar2000 would show the Peak meter as going over 0 dB.As I started raising the bitrate, since I already knew the exact spot where to look, I could still hear the volume difference. So I started getting suspicious, I decided to switch codec to AAC (using qaac), same results. Then I tried LAME, same result.Now, I know I've read something about this before, but can't find a single compound answer. I got tired of comparing files yesterday, but I have a feeling that if I normalize the source volume first, and then compare THAT to the codec's result, I wouldn't be able to hear said volume difference.