claim: Tenacious D was certified platinum.
evidence: The Itakura -- Saito distance -LRB- or Itakura -- Saito divergence -RRB- is a measure of the difference between an original spectrum and an approximation of that spectrum .. spectrum. spectrum. Although it is not a perceptual measure it is intended to reflect perceptual -LRB- dis -RRB- similarity .. similarity. similarity function. It was proposed by Fumitada Itakura and Shuzo Saito in the 1960s while they were with NTT .. Fumitada Itakura. Fumitada Itakura. Shuzo Saito. Shuzo Saito. NTT. Nippon Telegraph and Telephone. The distance is defined as  :. The Itakura -- Saito distance is a Bregman divergence , but is not a true metric since it is not symmetric and it does not fulfil triangle inequality .. Bregman divergence. Bregman divergence. metric. Metric ( mathematics ). In Non-negative matrix factorization the Itakura-Saito divergence can be used as a measure of the quality of the factorization  : this implies a meaningful statistical model of the components and can be solved through an iterative method .. Non-negative matrix factorization. Non-negative matrix factorization. iterative method. iterative method