Wednesday, March 4, 2015

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!

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