Digital audio editing software

February 11, 2017
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top and tail 2This document addresses some basic techniques to help you when editing digital audio. It assumes little or no previous knowledge and experience of audio editing and offers advice on how and when to use common tools within the editing environment.

Introduction

Editing audio digitally offers a multitude of possibilities for manipulating sound. From getting rid of unwanted noises to sonically re-shaping a recording beyond any recognisable form to the original, editing can be a very powerful tool. If you tune into a radio show, or play a music CD, what you hear will have been extensively edited. Beginning to edit audio files can be a daunting task and it is worth taking taking a little time to get familiar with the basics. Editing is a skill and improves with practice. Tasks that seem to take a long time will quickly speed up once you regularly work with digital audio.

When you import audio files into your editing software they can be cut and separated into regions and moved around within an arrangment. When you are happy with the arrangement of all the regions, have finished editing and done all the necessary mixing, you will then be ready to render the arrangement into a final audio file.

Common editing tools

Name(s)

Common Icons

Function

Comments

Select tool, Cursor

or

1. Selects and moves regions

2. Selects as area within a region

Zoom in/out

Zoom in and out of the current or selected view

Sliders at the edge of the window often perform zooming

Cut, Split, Scissor

Splits a region at the position of the cut

Useful for 'topping and tailing'

Glue,

Join

Joins regions together to form a new region

Fade (and/or) Crossfade

crossfade 1

Crossfades between two regions and/or applies a fade in/out to a region

Draw

Redraw the waveform at sample points. n.b. this can remove vitakl information from a file and should only be used in re-mastering

Useful when removing clicks or pops

Envelope

Gives control of the volume on a track, a way of automation

Solo

In play mode plays the selected track and mutes all others

Mute

In play mode mutes the selected track

Should I ‘top and tail' my audio files?

A very useful technique is ‘topping and tailing' audio files. This is the process of removing silence or noise before and after the desired audio section within a file or region. These silences are commonly from the pauses made at the start and end of recording. Diagram 1 below shows an audio file that is topped and tailed. The blue wave in (a) precedes and ends with silence. 1 (b) shows the waveform isolated with both the silences removed.

a)

b)

Diagram 1 - 1b is the resultant region after the silence at the beginning and end of the region shown in 1a has been removed.

Topping and tailing is done by cutting the audio region at two points to seperate the top and tail. The two new regions that are created as a result of the cuts are then deleted.

Cutting audio files at random positions can lead to unwanted audible clicks.

There are audible clicks where I have made cuts to my audio regions. Why is this?

To avoid pops and clicks when cutting audio regions always make cuts at zero crossings. A zero crossing is where the wave is neither above (positive value) or below (negative value) the horizontal zero line, but where it crosses this line. Diagram 2 below shows a waveform zoomed close up. The straight horizontal line is the zero line (which represents volume) and the dark grey area starts and finishes when the wavecrosses this line - it is actually at volume zero; the ideal place for making cuts. Cuts made when the wave is not on the zero line can create pops and clicks as the volume at that exact point is not zero.

Diagram 2 - The dark grey region highlights an area of the wave which begins and ends on zero amplitude, Y=0.

Another way to eliminate clicks at the beginning or end of audio files is to use fades. Read the section further in this document for more information on using fades effectively.

How can I remove unwanted noises from my audio files?

Imagine the following scenario. You are editing a spoken word recording where every now and then the microphone has picked up the sound of someone else coughing, which you wish to remove. This occurs:

A. During gaps between speech,

B. At the same time as speech occurs

Using the cut tool to isolate and remove regions of unwanted audio (as we've seen above) will, on the whole, rectify the problem raised during A.

Rectifying B, on the other hand, is more of a complex issue to resolve. This is because multiple sounds occurring at the same time are very hard to separate, and therefore any changes made to one sound will affect all other sounds that occur at the same time. In this example attempting to remove coughing during speech will result in speech being removed as well as the coughing. This highlights the importance of achieving clear recordings with minimal noise and interruptions. Achieving this will help eliminate problems such as this during the editing process.

Removing clicks and pops from recordings

Pops and clicks can come from a range of sources, but they are relatively straightforward to remove, even when they occur during audio you want to keep as they have very short lengths. The three key principles to follow are:

  1. Isolate the pop/click. Zoom in close and identify the beginning and the end of the offending sound.
  2. Cut either side of the pop/click region. Remember to cut at zero crossings.
  3. Delete the region of the pop/click and re-align the regions either side.
  4. Listen to the result. If you can still hear the pop click then you have not isolated the correct area. If the result sound unnatural you may have to experiment with the realignment of the regions and apply fades (see further on in this guide).
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