Basic Audio Editing
May 29th 2012
Whether
you’re setting out to write a dance track or editing sound for video
post production, basic audio file editing skills are an essential. Most
sequencing software ships with built in audio editing capabilities, but
stand-alone programs such as Adobe Audition, Sony Sound Forge and Bias
Peak Pro provide much more accurate and comprehensive features.
When preparing
digital audio for use in a project it’s always prudent to
scrutinise your starting point. For example downloaded sample packs
and sample CDs are not often as well produced as you’d think,
and may contain poorly cropped audio files that produce an audible
“click” when played. Correcting these errors is
relatively simple and can be accomplished in seconds. Apart from
these basic functions (such as cropping samples, fading in and out,
Normalise etc) audio editing programs also have the ability to apply
processes such as noise removal and more creative special effects to
your samples, either through built-in or VST/Audio Units plugins.
Zero Crossing points
are one of the fundamentals of digital audio editing. To understand
what a Zero Crossing is we need a quick science lesson. Sound waves
are primarily oscillations, and they oscillate around an axis known
as the "zero crossing point". At this point the negative
signal crosses over into being a positive signal, and vice versa.
This point is represented in audio editing software as a horizontal
line bisecting the middle editing window. When editing a sample it is
always preferable that a waveform starts, and ends at a zero crossing
to prevent audible “clicks” in the material after the
edit.
Fixing samples that
don’t conform to this principle is simple. Load up your sample
and zoom in so that you can see the sample’s waveform clearly.
Some editors such as Adobe Audition and Bias Peak Pro allow you to
reposition or draw the waveform to manually correct these errors, but
it’s just as easy to simple apply a fade in/out effect to the
offending portion of the sample. Most audio editing software
features a “snap to zero” or “search zero crossing”
function, making locating these points automatically easy.
More creative uses
of basic editing can make the most of your audio samples before you
use them in your project. For example drum samples can easily but
spiced up by applying gain or fades to their attack or release
portions to make them harder or snappier.
Many sampled sounds
don’t come with pre-determined loop points, which doesn’t
help if you want to load them into your sampler software (or hardware
for that matter!). Audio editors provide an easy way to loop samples
and save them in the file for future reference. A healthy knowledge
of zero crossing theory comes in handy here too, for example it’s
sometimes possible to loop a waveform from the top-most point of its
oscillation rather than a zero crossing. When searching for loop
points in a sample look for re-occurring patterns in the waveform.
It’s always best to keep your sample looping once you’ve
found your rough points, and then refine them so that there’s
no clicks or pops present. A note of caution here though: looping
can be a black art and not all samples, especially of the stereo
variety will loop easily. Affordable plugin samplers suck as Expert
Sleepers Cross Fade Loop Synth can make this process very simple.
Another useful
technique that’s helpful to apply pre-project is noise removal.
Samples recorded from the real world are often too noisy for use in
pristine digital environments, and noise removal processing can be a
savior here. Modern noise removal involves taking a sample or profile
of the offending noise (this can be used creatively too) and then
using convolution processing to remove these frequencies. Our
favourite editors, Adobe Audition and Sony Sound Forge have these
facilities built in.
See our glossary section for detailed explanations of music technology terms.
DMS
