15. De-clicking and De-crackling (part 1 of 2)
After you have installed the XFX plug in for Noise Reduction, Sound Forge will now be capable of removing most of the noises associated with vinyl. Before starting with this section, we have to realise that vinyl noise is made of three different noise levels, each needing a different process to remove. These are:
Surface sound: (rumble) This sound is obvious on all records regardless of its condition. This usually generates a sound signal around the lower frequencies of the sound spectrum. Although this sound is not a obvious annoyance when playing music of a moderate amplitude, this can be more audible on quieter pieces of music where they are softer passages, or classical music. Also as discussed earlier, rumble is notable on records pressed with micro-groove technology. This uses a tighter spiral track on the record, decreasing the amplitude in which music can be recorded, thus drowning the audio signal further into the surface sound threshold. This sound generally appears in the 0 cps to 80 cps frequency range, and is easy to remove. (cps = cycles per second)
Needle Drag: This is kind of the same sound that is associated with tape, but not obvious. This sound appears across the mid to high frequency range, and like crackling, can be tricky to remove. As the noise appears in the same frequency range as percussion and higher end instruments, attempts at removing it can also damage the original recording, as many of the programs available cannot distinguish between the hiss and instruments. For some reason, this noise fluctuates with different record pressings, and is not as audible on better quality records, and higher end turntables. This sound appears in the 5,000 cps to 15,000 cps frequency range.
Pops and Crackles: This is the noise that gives vinyl it's classic feel and some say, a certain kind of warmth, yet for many of us music lovers, it's the noise that makes listening torture. There's nothing like that delicate passage of music, interrupted with a huge pop. This sound generally appears in the 0 cps to 5000 cps frequency range, and is one of the hardest vinyl imperfections to remove.
(my opinion only) This is one of the hardest sounds to remove as much of it is often the same frequency as the music. Many attempts in removing the crackling noise have resulted in poor restoration results. There has been two different processes of removing this sound. The first is frequency filtering, This tells the program to remove frequencies of a certain pitch and range. Unfortunately many programs cannot distinguish between what is the crackling and what is the instruments. This therefore results in the program removing sounds from the original recording. If a certain noise imperfection is the same frequency as a particular instrument, the program will remove all noises from that frequency. The second process in removing cracks and pops is "patch and replace", which delivers much better results then frequency filtering, but still can leave artifacts in the processed file. This method is discussed further in detail, in the next section.
If I'm wrong, I'd be happy to hear about any programs that can actually clean up records without destroying the music. E-mail me at email@example.com. Any company is welcome to send full-working software versions, for evaluation and review on 2PR's LP2CD Section.