Ayke Agus, a student of Heifetz, wrote in her book that Heifetz cared more about how you looked than how you played. I never thought much of that statement until watching the video from the post labeled "Paganini with an Operatic Vibrato". Her main flaw seemed to be her posture. Therefore the video got me wondering on how posture affects ones sound, and I thought that I had better do some experimenting. I found that both when sitting and standing, different facets of my playing changed, as I assumed different postures. The factors included the height, and position of the instrument on my collarbone, and the position of my feet and how I distributed my weight. It was surprising to me how different not only my tone was as I changed my balance, but the control of my vibrato and shifting. From the "Paganini with an Operatic Vibrato" post, I now understand why her vibrato was so vapid. I was never taught how to stand or sit, when playing the instrument, and I wonder why. Is there any opinion on the correct way to sit/stand? I guess this mainly applies to the flexibility allowed without a shoulder rest.