Birds like these 6 species (and there are many more tapaculos) are so similar that you need their distribution maps to identify them. The voice is a good ID feature but not very easy to describe in a book, especially one written by a Dutchman for English-speaking people
Humans and (other) mammals produce sound in their Larynx, an organ at the top of the windpipe. Air is pressed through a slit between vocal cords (VC) forcing them to vibrate.
A = windpipe, B = Oesophagus, C – valve between A and B, T = tongue
Birds produce sound in their Syrinx, an organ much deeper in the chest, where the windpipe (A) splits in two long pipes (P). In this soundbox there are labia (L, lips) whose form and tension is regulated by an inflatable air sac (S) and a system of paired muscles (M 1-4). Songbirds (or passerines) have a system of 4-7 muscles. Non-passerines have either none or 1-3 pairs of muscles. Note that many birds can produce sound in both lung pipes, producing different notes at the same time