The frequency of the applied bias signal. Generally, about 150,000 to 180,000 Hz.
"I just wanted to let you know that I was very satisfied with the CD you made for me from a really old album my husband had. It is very clear and without background noise - he almost misses all that hissing. He was so excited to have it and couldn't believe I had found a place to transfer the music by looking on the internet. Thanks again,"