The goal of the standard was to prevent the highest peaks of the particular recording from going beyond 0 dB. The 1630 Sony machines which were used as the transfer medium between Mastering and CD production had a readout which told you if the peak level had been exceeded during the recording or playback of the tape.
If 3 consecutive 0 dB levels were detected, the recording was rejected because of the certainty of a clipped or distorted waveform. I had 3 of these machines in my room at the CD plant and spent years doing this until the advent of CDR masters, and then internet supplied DDP masters made the very large and complex 1630 Umatics obsolete.
So the most important order of business in the production of CD's, as it was with the production of vinyl records, was to prevent the highest peaks from being distorted in the transfer to the final consumer product. (Cassettes were exactly the same)
If you have followed this blog and watched the videos, you have a good idea of why we have to keep the actual samples to -1 dB or less to prevent the resultant waveform from going above 0 dB. There of course are waveforms that could go above 1 dB over the sample level on either side of them, but the vast majority will fit comfortably in this parameter. If a recording has waveforms that exceed that level, the waveforms can be individually lowered, run through a limiter, or the entire recording lowered in level to compensate for that peak.
I have done all of the above at some point and each method has pros and cons. With modern software, it is simple to do one or all of the above fixes.
What we have with modern pop music is a situation where the music has such a small dynamic range that there is rarely just one peak at the highest level. The song is compressed and limited to the point that every beat is at the maximum level. So instead of dealing with one or two peaks, you need to use software to deal with thousands of peaks, or lower the level of the entire recording away from the 0 dB mark.
The previous blog showed how 100% of the masters from the Grammy's 2016 CD were incorrect in the simple parameters that we have described here.
Obviously these things are not obvious. We will examine some more soon.