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 mark@2prfm.com.  Any company is welcome to send full-working software versions, for evaluation and review on 2PR's LP2CD Section.

PATCH AND REPLACE CRACKLE RESTORATION.

First remove rumble

We need to remove the rumble before any other process, as the other processes will mistake the access rumble for crackling.  This is because Sound Forge removes noises based on a mathematical equation, in the form of a wave as shown below.  Sound Forge's De-crackler will calculate the pattern of a particular wave form as shown in waveform 1 of figure E.   The program will then repair the crack in waveform 2, by redrawing the waveform in the same pattern as waveform 1, based on the mathematic equation derived from the pattern of waveform 1.  Sometimes these large bumps in the wave can be created from a sudden burst of rumble noise, hence the importance of removing rumble first before any other function.

(figure F)  To do this we need to first select the entire track. (1)  Then we select process.  Go down to EQ and then select paragraphic from the sub-menu.  You will then have a dialog box that looks like this. (2)  Go to the presets and then open the drop-down menu.  They should be one titled "(sys) Remove very low and inaudible frequencies below 20Hz".  This function will remove any sound frequency that falls below 20 cps (20 cycles per second).  Although rumble carries through to the 80 cps range, I prefer to just remove the bottom 20 cps, as this is where 75% of rumbling occurs.  You can try the next setting up, which will remove all noises from 0 cps to 80 cps, but this may also make some low end instruments sound hollow. 

After clicking on the "ok" button, your computer may take a few moments to process the sound.  You will then notice a small change in the shape of the wave form.  You now have successfully removed the rumbling noise from your recording.