All records and tapes, no matter how pristine their condition and no matter how expertly recorded, will have some noise. Along with noise due to surface imperfections in the media, some electrical noise will be picked up as the signal travels through various analog circuits and cables on its way to the analog-to-digital converter in your sound card. And even then the signal is not safe, because the analog to digital conversion process adds a type of noise caused by “quantization errors” (see Chapter 8).
But don’t worry—noise is only a problem if the level is high enough to interfere with the sound you want to hear. Noise that’s below a human’s threshold of hearing (see Chapter 8) is nothing to worry about.
Even noise above the threshold of hearing is not necessarily a problem if the material masks the noise. (See Chapter 10 for an explanation of the masking effect.) For example, noise (such as clicks and pops) that would be very annoying in a solo classical piano recording would be much less apparent when listening to a heavy metal cut.
Noise comes in many shapes and sizes, so the settings in your noise-removal tools should be fine-tuned for the characteristics of the noise you need to remove. Following are descriptions of several types of noise common to records and tapes.
Hiss (a common type of broadband noise) is fairly easy to remove, though hiss within the recorded material is difficult to identify because it is mixed in with the rest of the signal. ...