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.