Luckily, for whatever type of audio that you need, there is a free-use version of it somewhere on the internet. If you find something perfect and it's ok to use it, then download it and you're done! Cautionary step : do make sure that you have permission to use the online audio you select. The fact is though that you often need to take further steps to change whatever free-use audio you find so that it fits your vision. If this is the case you will need to edit audio, but it's a lot easier this way than starting from scratch. If you haven't tried finding something which at least resembles what you need for free on the internet, it's probably the right move to do so. Freesound is great for SFX and many small time musicians will let you use their existing music if you credit them (check out SoundCloud).
So you've decided that editing together the audio you've found is the right choice for you. This can mean anything from changing the length of a song, the volume of an audio asset, or compiling a number of different sounds into a new sound effect. As you may have already realized, there is a lot to audio editing and the process can seem quite complex. But there are a few tools which are easy to understand and can go a long way.
As far as which software to use, there are a lot which edit audio, but for sake of simplicity I'm going to be discussing how to edit audio using a free and very helpful program called Audacity (download here). If you'd prefer not to use Audacity (Garageband is a good alternative for Mac users), most all of the tools I will be discussing are still there, probably have the same name, and will simply have a different look or be in a different place. For clarity though, I do recommend Audacity and will optimize this guide for that program.
So, you've downloaded Audacity and opened it up. It might seem that there are a lot of buttons at first, but not all of them are equally important. I've highlighted some of the most important areas in red.
The lower label around the large dark grey area titled "Audio Manipulation Area" is where a visual representation of our audio will be once we load it into Audacity. This is also where we will be doing most of our editing. At this point, we are going to load our audio into the Audio Manipulation Area.
Loading the audio into Audacity, depending on your version, can actually be as easy as dragging and dropping your audio file(s) over the Audio Manipulation Area. Alternatively you can click the 'file' tab on your window's tool bar and select 'open', just like any program. I have never experienced difficulties with loading certain file types, but if you do then consider reading the section about converting your file type at the end of this article.
Once the file is loaded, it will appear in the Audio Manipulation Area. At this point the visual representation of the audio file is called a 'track' or an 'audio track'. It may be that even if you uploaded a single file that two horizontal representations of the audio appear. This is an indication that it was a 'stereo' file rather than a 'mono' file which means that there are two versions of one audio event being played simultaneously: one for the left speaker of a sound system and one for the right. Stereo files have a unique capacity to create a sense of space in an audio asset.
Other buttons that are pretty key are the basic tools buttons. To one side of the Media Controls section are six buttons in a small grouping. These are some of the primary editing tools you will be using. Of these six there are three which are extra important. Below I've highlighted and labelled them.
Great! You've come a long way and are ready to get your hands dirty with audio editing. Depending on what you need for your audio asset, there might a variety of appropriate next steps. In order to address your particular needs, I will create a series of different sections for different basic audio editing tasks. An important final step after editing your audio is exporting it to the most appropriate file type. Directions on exporting and converting will be in a section at the end of this article.
Shortening an Audio Asset
Changing the length of an audio asset is a loaded topic, depending on the direction which you want to change it can either be quite complex or relatively simple. Lengthening an audio asset involves generating or otherwise acquiring new audio material to extend what you already have. Shortening an audio asset can also be approached in more complicated ways, but can be as basic as deleting unnecessary sections of the track. I'm going to approach how to shorten the audio asset by deleting.
We can decide what parts of our audio track are most important (and should be kept) by playing through it and considering our vision. Once we know what parts we want to keep, use to selection tool to highlight everything except those parts. Next hit 'delete' or 'backspace' on your keyboard. Wasn't that easy? At this point you may however want to also put in a fade (a smooth transition to or from silence) to smooth over the sharp deletion.
Fades and Other Effects
Fades can really do wonders, and never really become irrelevant in audio editing. A fade in will fade from silence to the volume of your track. And a fade out will fade from the volume of your track to silence. We will be using a sound effect to accomplish our fade. Sound effects (also called audio effects) essentially carry out specialized processes and tasks on audio and are endlessly helpful. Fade effects can be used simply in Audacity by selecting the section you want your fade to occur during with the Selection tool and going to a great little tab on your window's tool bar called 'Effect'. About halfway down the list that will appear are the effects we're looking for.
Changing Volume and Pitch
Volume and pitch are very common aspects of a sound which are changed. Volume can be accessed by something called a fader on the leftmost side of your track (highlighted below with a red box).
Adjusting pitch can be done using another effect. View the earlier section titled "Fades and Other Effects" if you're unsure what an effect is or how to access it. One of the topmost in the list of effects is one called Change Pitch, which does exactly what it seems. There are a number of things which you edit in the Change Pitch window after you select it, but the most important ones are called "Percent Change" and "Semitones (half steps)". In the image below the "Percent Change" scale [below] and "Semitones (half steps)" scale [above] are highlighted in red.
Most of the hard work is done, but getting this final step right is important. All digital audio comes in a file format (a way of storing digital data), and all of these different formats deal with the audio in different ways. The most important difference between these file formats for most people is file size/audio quality. The two can be conflated most of the time since they largely rise and fall together.
Though there are many types of file formats (many specialized for specific purposes), two fairly universal ones are WAV and MP3. WAV files have a bigger file size and better audio quality and MP3 have a smaller file size and lower audio quality. Audacity can export in a number of formats, but interestingly needs additional software to export to MP3. I personally have had trouble with this software and have used this nifty conversion website in the past. Alternatively there're a number of programs for free on the internet which do the same thing.
Well, that's all the basics. I hope I helped and good luck with your editing!
Feel free to contact me with any questions.