The frequency of the applied bias signal. Generally, about 150,000 to 180,000 Hz.
"March 2016 I sent a 8" audio disc recording made in 1942 of my husband singing the Hansel part from Hansel and Gretel in his high school production at age 13. The homemade recording had deteriorated with scratches and extensive surface damage which made it impossible to play. But CVC was able to transfer it to CDs and capture listenable ..."