What happens when a professional singer, musician, composer, arranger, and producer are also a vocal coach? Well… he hears more than most and also knows music more than many vocal coaches. What does music have to do with singing? Think about it.
Many vocal coaches study vocal technique with a vocal coach for years. They then go off on their own, thinking they are ready to instruct. There is a technique to teaching vocal technique. There are thousands of things to analyze, potentially. There is listening technique. What and how you hear and to what extent will affect your analysis of a voice and whether you get it right or wrong.
If you work with a group and you cannot hear heterodyne, let alone know what it is, you won’t do nearly as good of a job as one who hears it and also understands partials, or the overtone series. There’s much more to it than one page can allow.
Pity the person who relies solely on an audio or video course on singing. The most important component is omitted from that scenario. Just as a surgeon who operates on himself has a fool for a patient, a singer, self-taught, even with the best video course in the world, has no real objectivity or musical education to get very far.