I got this book "The Neo Soul Guitar Book" and they have audio files and videos, all helpful. But I just can't understand how musical notation or guitar tabs should be read here. Just the first few exercises, we are suppose to do some hammer-ons. From the video or audio file, it sounded exactly the same but the notation provided by the book isn't the same. Please let me know how I should do the hammer-ons. Besides the tempo, the audio for both were same, 3 notes played then hammer-on to Emaj7. Thanks in advance!
In the first tab (score) you are playing the chord E6 on the down beat then hammering on the maj 7 on the up beat. In the second tab it looks like they are trying to express the same action with a grace note. The idea there being that you borrow a little time from the beat to play that note then play what is on the beat. This can be a little confusing. The notation is really meant to be interpreted the same way as the tab in pic 1. You play the full chord with the leading grace note on the beat and quickly hammer on the second note.
In music language as in any other language you have the written version and the spoken version.
What you're seeing here is a grace note which basically tells you to steal a little bit of time from the original note in order to play this "non-essential" note.
How to interpret it is subject of debate. It depends on the period or composer.
When it comes to modern music I try to listen the audios and learn it as an idiomatic element. In other words, I listen repeatedly the audio or watch the video in order to accurately imitate the desired effect.
My recommendation is: Use the audio as a reference too. And imitate a lot. This way you'll be able to develop your own criteria as well.