Editing Audio

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Revision as of 15:38, 2 January 2011 by Philchenevert (talk | contribs) (While Recording)
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How to, why to, tips & tricks

Why To

See Audio Processing Concepts

How To


While Recording

There are a few things that you can do while you're recording to make the editing process easier later on.

  1. As soon as you make a mistake tap the mic three times, or say a really loud "MISTAKE!". Then repeat the sentence that you goofed up. The point is to create a spike in the sound waves of your editing software. This allows you to more easily find your mistakes in the editing process. [Some people with delicate mics, just click their tongue twice; this also gives nice easily seen spikes]


The process of editing simply involves removing the pieces of your recording that shouldn't be there. Read the instructions for the recording software that you're using. It should tell you how to remove sections of a track, and edit out pieces.

Try to avoid too much processing through filters on your recording. Excessive alterations to the sound can sometimes cause additions like a metallic quality to your recording. A little background noise is OK. If you're unsure how much is too much, ask a fellow volunteer to lend their ear. See [:ImproveYourRecording:How to Improve Your Recording] for more tips.

If you created a sound spike after your mistakes.

Main Page: Deleting errors in Audacity and Alternative Editing Method

It is possible to edit your file without listening to the whole thing to find the mistakes; you can just search for the editing spikes. When you find a spike, listen through to the recording around it, and delete the mistake including the spike. Make sure you find someone to proof-listen your recording if you don't listen through it yourself during editing

Common Keyboard Shortcuts For Audacity

Ctrl S = save Ctrl C = copy Ctrl V = paste Ctrl Z = undo Ctrl N = new Ctrl A = select all (selects the whole file) Ctrl O = open

Ctrl W = close Space bar = play and pause

Tips & Tricks

Cleaning out noises during silences

Between sentences and paragraph, it is better if the silence is total. However, there are often small noises like mouth/lip noises, breathing or blowing into the microphone, chair creaking etc. all the more so as the reader takes the ooportunity of this silence to sit back, relax, breathe, or whatever. The basic command in audacity is Ctrl L: select the silence, then hit Ctrl L to turn it into true silence. You can leave some noise, like the short breath right before the new sentence starts, so that we know this is no machine-generated audio-book.

Trimming silences to a consistent value

You may want to make sure silences within paragraphs all have roughly the same duration (e.g. all between 0.5s and 1s), and all silences between paragraphs another duration (e.g. all between 1.5s and 3s). Apparently, Audacity does not have an automated command to trim all silences at the same length. The basic solution is to select the amount of silence you want removed, and cut it Ctrl X. Conversely, to increase the duration of a silence, select the amount of silence you need to add, hit Ctrl C (copy), then Ctrl V (paste) twice (one in place, then duplicate).

Anyone has something quicker ?

Making sure the edits are transparent

Sometimes, the 'edges' of an edited portion make a distinctive 'clicking' sound. When you zoom in, you see that there is a discontinuity in the signal (a sharp edge). To remove this, you need to cut (or add) signal so that the transition is smooth. The easiest way to do it is to start and end all your selections (when you want to cut or when you want to paste) at samples where the signal has a zero value, and place the cursor (in case you want to paste) at another sample having a zero value. That way, you ensure that the signal will have a zero value on both sides, thus ensuring continuity. Zero values are not hard to find: there are several hundreds of them each second.

In Audacity, Edit > Find Zero Crossings, or the Z key, moves the edges of the selection slightly until they are close to a zero crossing.

For the perfectionist: the selection should start and end with a zero value and also with a rising signal, and the cursor should also be placed on a zero with a rising signal. With this technique, you can now edit out (or in) not only sentences or words, but individual syllables. Try shortening an 'aaaah', or stretching a 'oh'.

Joining several MP3 files into one

If you have several MP3 files that you wish to convert into one, long file (eg if you wish to combine a set of chapter files into a single book file), there are a couple of ways that this can be done.

If you are using Linux or a Mac with OS X, you can use the cat command from a terminal. To join the contents of files 1.mp3, 2.mp3, and 3.mp3 into one file named out.mp3:

cat 1.mp3 2.mp3 3.mp3 > out.mp3

Alternatively, you could use the MP3Wrap program. It's released under the GPL and is free to download. Versions are available for Linux and Windows.

Does anyone know of an equivalent for the Mac?

Since OS X is built on top of a Unix kernel, the cat command certainly is available from the OS X command line as well.

Splitting an MP3 file into shorter files

If you need to split MP3 files into shorter recordings, the Mp3splt program should work. It's released under the GPL and is free to download. Versions are available for Linux, Mac and Windows, and there are command-line and GUI (graphical user interface - point & click) versions available.

Using a Drawing Tablet

Using a mouse for extended periods of time to edit can be painful and uncomfortable. If you have a drawing tablet, consider using it for editing. Set any function buttons to the keyboard shortcuts for cutting sections of audio, and saving. This saves time, and discomfort.

Example: Kristin uses Audacity and a Wacom drawing tablet. There are two buttons on the pen that she has set to CTRL+X (cut in Audacity), and SPACE (play/pause in Audacity). One of the function buttons on her drawing tablet is set to CTRL+S (save). Deleting a piece of audio is a simple drag of the pen to highlight, and click of a button on the pen. She then hits the second button to resume play, listening for more mistakes.