Difference between revisions of "Deleting Errors in Audacity"
(Transcription of page from old wiki.)
Revision as of 00:43, 7 June 2009
Removing known repetition-errors from a recording
One of the commonest recording errors is a slight repetition or a correction (e.g. ".... then, as she went ... walked down the street ..."). In essence, errors like this can simply be chopped. The more precisely you make your cut, the cleaner is the final sound.
Often, when a recording has been passed to someone else for checking, the result will be a list of errors, each error with a note of the time at which it occurs in the recording. Whenever you edit an error in the file, you change the length of the file ... which means that you also change the locations of any errors following that one. If you have a time-list with more than a couple of errors to correct , you should always do your editing by starting at the end of the recording and working towards the beginning. This way, as you work your way through the file, the edited part of the recording lies behind you, and the timed errors lie untouched in front of you.
If you are correcting a lot of errors, save when you finish each correction, as you'll lose a lot of work if Audacity crashes.
The most important thing to learn is to use the Zoom (Tip: For an illustrated "Beginners Guide to Cutting Audio," click here):
- Zoom out enough to make moving through the file much faster.
- Highlight, listen, then zoom in or out to define your section for editing.
- When editing, zoom in and in until you can identify the boundaries between sounds.
Editing out an error consists of:
- zooming into the section you're going to operate on;
- finding the front and back boundaries of the section to cut out;
- deleting this section and checking the result.
Here you go, step by step:
- If you're editing an mp3 file, open it in Audacity, then immediately save it as an Audacity file. (It helps a lot to have the file of the original text open at the same time as you are editing.)
- Now go to the time of the last error that's on your list:
- Move to the correct area of the Audacity file, using the scroll bar at the bottom of the display, and zooming in or out so you can step quickly through the file. When you have found the right time spot in the file, highlight the area that you think includes the error, then play it. If it's not what you are expecting to hear, search the text file for what you've just heard, so you can find out where you are in the Audacity file, then hop through the file, listening to fragments until you get to the proper section.
- Now zoom in and highlight the affected section of the recording. You should include a little of the recording before the error, the error itself, and the bit of the recording that will replace it (I've called this the "correct" bit in later steps). Listen to it, watching the cursor, to get an idea of the areas that you are going to be looking at.
- Highlight the front end of the "correct bit" and play it. Drag the left boundary of the highlit section, left and right, listening to the effect, until you have found its start point. You may need to zoom in for this. I tend to make a mental note of the shape of the waveform at that point, rather than making a note of the exact time, but you might prefer the latter.
- Now highlight and play a section of the recording which includes the error that's going to be chopped out, plus a few seconds of the recording before it. You need to find the point where the earlier, correct, part of the recording becomes the bit that's going to get chopped out.
- Highlight the small section across this boundary and zoom in until you're looking at perhaps a couple of seconds (or less) of the recording. Play it. You can tell by listening and watching the moving cursor approximately where the boundary is: put the cursor there, then drag the highlight in turn to left then to right, and play the highlit areas. Ideally, you want to cut out none of the correct part of the recording, and to leave none of the error behind. You will probably need to repeat this listening check, readjusting the cursor position until you get a reasonable boundary location. Leave the cursor at the boundary.
- Now zoom out until, as well as the cursor, you can see the start point of the "correct bit" that is going to replace the error. Drag the highlight from your boundary location to that point and delete the highlit section. (If you want to be extra cautious, and there's some silence between the error and the replacement, you can end your deleted block within this silence, and adjust later, cutting out silence until the recording sounds okay.) Zoom out a little and listen to the flow of the recording across your deletion. You may need to undelete and have another go, or perhaps insert a fraction of a second of silence copied from somewhere else in the recording, to make the break sound better.
Removing unwanted silences from a recording
- When working on chapter two, I stopped the recording in the middle of the chapter to get back to it in the morning. Apparently, I did not stop the recording until some fifteen or twenty minutes after I ended. As a result, I have this long stretch of nothing. I had taken my microphone off, but had forgoten to stop the recording. The recording resumes some twenty minutes later on a different track. How do I get rid of this long stretch of nothing and move it to the same track?
Zoom out some and use the mouse to select the long stretch of nothing, then hit Delete. Then use the double-headed arrow tool up in the left-hand corner, and drag your new track to where you actually want it to start. You can then either:
- select all, and use the Quick Mix function (under the Project menu) to merge the tracks, or
- select, cut and paste the new track onto the end of the first track, then delete your 'extra' copy of the second track.
There is often an audible click after you have cut a section of the recording. This is because the part of the waveform before the cut does not match up with the part after the cut. It is best to ensure that the cut starts and ends on a zero-crossing of the waveform, preferably a rising-edge zero crossing.
In Audacity, Edit > Find Zero Crossings, or the Z key, moves the end points of the selection slightly so that the selection starts and ends on a zero crossing.