How can correct turntable speed as well as excellent speed stability possibly NOT matter and be of the utmost importance? Rhythm and time is where the heart and soul of music lies. Any technical considerations that may have an effect on these are of the utmost importance. I am constantly perplexed by how often audiophiles agonize about minute changes in areas that affect the tonal/timbral characteristics of their audio systems, but are willing to forgive much larger deviations from truth in the area of time and rhythm.
I hope we can agree that our audio systems exist to be at the service of the music. Musicians, not audio systems, make music; and musicians give a great deal of importance to performance considerations that relate to the perceived effects of correct playback speed and speed stability. The changes in pitch as they relate to performance standards are more subtle than what is generally discussed in relation to technical accuracy in turntable systems. These considerations are not arbitrary, but relate to the emotional impact that tuning has on the music. This is not only the players' consideration, but sometimes also the composer's intent. It is well
documented that many composers chose to compose in a particular key because of the emotional effect of one key versus another. Likewise, orchestras or individual players will often tune their instruments to achieve a particular sound and it's resulting emotional effect. If we are going to worry about the effects things like slightly raising or lowering VTA, why dismiss the effect of these other considerations when these relate much more to the core of the music?
Speed stability is even more important as it relates to these considerations. Excellent comments have been made above about the importance of these. There is no question that extremely subtle deviations from absolute pitch stability are quite audible. As has been pointed out, even the very best belt drive tables suffer from these distortions. What is really insidious is the effect that these distortions have on the emotional impact of the music, and the ability of the music to engage the listener. As this relates to musicians' performance standards, I would like to point out that the effects from the absence of absolutely stable playback speed on the music is not nearly as subtle as the considerations that musicians give to absolutely stable and accurate time and rhythm during a performance; these can be the effect of anything from simply the mediocre sense of rhythm on the part of a particular musician, to wether a musician had too much coffee that morning (I kid not). If we can agree that these things matter during a performance, how can similar effects not matter a great deal during playback?