Wednesday, March 4, 2015

08 Removing clicks in the recording manually

Scratches in the quiet parts of the LP grooves are often difficult to eliminate, because they stand out so in contrast with their immediate neighbourhood. You may like to deal with the worst of them manually, if they still remain after a few passes with the automatic click removal routine (see previous post). Such large clicks or thumps are more frequent in the initial parts of the recording, from the outer portions of the vinyl platter.

Audacity provides ways of dealing with such persistent and awkward defects. The most laborious way is to zoom in on the portion with the magnify tool (the magnifying glass + icon, or you could select a small portion and maximize it with the right-most magnifier tool) until you are able to see the individual data elements as discrete (separate) dots on the wave-form, as we can see in this sequence of screen shots.

Having zoomed in till you can see the individual dots (the sampled points), you then choose the ‘pencil’ icon from the top-left panel. With this tool, you can click and drag it across the screen to draw a new wave shape, to smooth out the sudden spike. Initially, to get the feel of it, you can click on (or just above or below) each dot separately to reposition it. 

As you get comfortable with this procedure, you can graduate to a free-flow redrawing of the wave envelope. You needn’t despair if some of the time you go outside the line you’ve set for the new wave, since you can always correct it as many times as you want. I like to give a slight up-and-down shape to the sequence of dots, so that it doesn’t result in a sudden silent patch (a hiatus) in the sound stream. The maxima (peaks and troughs) have just to be within the broad limits of the neighbourhood to mask the spike (since there won’t be any musical sound there). The result looks like the following.

If you compress the wave display back, it looks like the normal up-and-down wave form without the peak that touched close to the top or bottom of the channel display (db or decibel level +1.0 or -1.0 in the display). 


If the thump is very broad and extreme, it may not be not be easy to do this as it occupies a wide patch. You could even just select the offending portion (a fraction of  second in practice) if it would not compromise the recording completely. Another option is to use the Effect-Compress operation, on a selected portion containing the broad thump. You should experiment with different settings in this, and you can Preview the effect before making it final.

Just remember to Save the edited recording frequently (use Save As and give new names, tagging on something like –ed or –new to differentiate the corrected bits)! This is one reason I like to slice the raw recoding into small chunks (I like to use 2-minute bits) – in case you goof, it won’t be that difficult to retrieve thee situation. And keep the raw recordings (the entire recording as well as the unedited segments) until you have done the cleaning up on all the segments and put them all together to your satisfaction: you never know what mistakes will have crept in (like missing out a segment, wrong sequencing, and so on).


I'll describe Groove Mechanic next post!

07 Removing clicks and pops in the recording

We now come to the crux of the matter, the actual cleaning up of the sound. The most obvious defect of vinyl playback is the frequent loud clicks where the needle had to cross a scratch on the surface. Since the scratch may have extended a few millimetres across the grooves, you can expect the click (sometimes it’s loud enough to be called a thump!) to repeat at regular intervals across a length of the recording. This is probably the first thing people would like to attend to.

You open the first segment of the file (remember we have divided the recording into 2-minute segments) in Audacity and take a look at it.  To display different proportions of the file, we use (click on) the ‘buttons’ on the top right corner with the magnifying glass icon. The one with the arrow head marks toward the middle ―<>― (where the pointer is positioned in the adjoining picture) will display a selected portion on the screen, while the icon to its right (with the arrow heads at the ends  >――< ) will display the entire file in a compressed form on the screen.

By clicking on the fast rewind symbol on the top left, you can display the start of the recording; then by clicking on the magnifier+ symbol on top right corner, you can stretch or expand the  displayed sound form so that you can see more details of the waveform. Another way of doing this is by selecting a small portion (by click-and-drag, or shift-click as per common usage), and then click on the magnifier icon as shown in the following pic.
 The expanded  display of this fraction of a second shows the sudden peak and trough in the sound wave that actually shows up as a loud click (the peak and trough indicate the amplitude, or volume of the sound; it registers as a click or thump because it stands out against the neighbouring sounds).

 Our job now is simply to reduce the peak and trough and bring the sound wave back to the ruling amplitude in the immediate neighbourhood.

There are many alternate ways of doing this. In previous versions of Audacity, there was no specific menu option to ‘remove clicks’, but I just discovered that there is such an option in the latest version under ‘Effects’.

You can fiddle with the levels of correction (using the sliders) to choose the threshold levels and the width. If the threshold is lowered, even small clicks will be smothered; too much of this may interfere with the actual sound recording (think of sharp percussion or metallic sounds!). The width also can be chosen; there is also a preview option (the lower slider). This is obviously the most painless way of doing it, and will result in a file with all these spikes ironed out. The sound is still there, but is not audible because it's only as loud as the preceding and following sounds. One could also exercise an option in how much of the recording is to be selected for doing the operation; if you select a small portion, then you could try different levels of sensitivity, preview after each change in levels, and finally settle for the best combination. If you’re not satisfied by the first run, you could repeat it on all or just a portion till you are satisfied.


The second, and laborious, way is to do it by yourself for each spike, manually. This may become necessary if the spike occurred in a relatively quiet portion (Beethoven is notorious for such low-amplitude stretches!), or if you have an older version of Audacity without Craig DeForest’s ‘click and pop removal’ (although it’s so easy to download the latest that there is really no need to soldier on without it!). There’s also a third option, using another program called Groove Mechanic by Coyote Electronics. I’ll show this next post!