Combining audio files

I am trying to combine (in sequence) three audio files (the file sizes are: first file is 23.6 Mb, second file is 4.74 Mb and the third file is 935 Kb).

As the process starts, the estimated time of completion starts at about an hour and continues upward; at about 6 hours of estimate I just cancel the operation.

Why would the program take hours (again, I don’t know when the estimate stops) to combine the three files listed above ? I am following what I have read to be the correct procedure to do it.

Any information appreciated.


It shouldn’t take hours. What format are you exporting to?

If you’re not exporting to WAV, try WAV just as an experiment.

Note that the file size of the exported file may be different from the sum of the sizes of the original files, depending on the format.

Thanks for the reply, DVDdoug.

I am exporting to MP3.

This additional bit of info may be of use (I didn’t bring it up before because it did not seem to be relevant): Initially I had three MP4 video files and had to get the audio from them - so I used Audacity to do that, which resulted in the three mp3 files that I listed in my original post.

Could the fact that the audio was copied from the original video files cause the audio files to ‘refuse’ to be combined ?

As you can tell, I am new to audio / video editing. I am doing it in order to put recorded church sermons on the church website.

Any info appreciated.


Using MP3 as an intermediate format is a bad idea. MP3 encoding always reduces the sound quality, so what you are currently doing is,
Starting with an MP4 file (the MP4 encoding will have already lowered the sound quality from the original video),
Importing into Audacity (this decodes the MP4)
Exporting as MP3 (this encodes the audio as MP3 and reduces the sound quality)
Importing into Audacity (this decodes the MP4)
Exporting as MP3 (this encodes the audio as MP3 again and reduces the sound quality further).

If you must export files as an intermediate step, export in WAV format. WAV files are bigger, but there is virtually no loss of sound quality.
Import audio from the MP4 files,
Align the tracks end to end (Select all of the tracks with “Ctrl+A”, then “Tracks menu > Align > Align End to End”)

Perhaps you are about to run out of disk space?

Please tell us what version of Audacity you are using (all three numbers, see the pink panel at the top of the page).

Are these sequences on separate Audacity tracks on top of each other? If so I think you have hit a bug as described in the release notes for Audacity 2.1.2 (see the first item):

So, just wait for the dialogue to complete (regardless of how long it states, it will complete in normal time).


Thanks for the replies and info, steve & Gale.

steve, that is a different method than what I have been using; I have been selecting the file to append, doing the ‘find zero crossings’ thing, cutting & pasting, I have plenty of disc space.

Gale - I am using 2.1.2

I shall try the combine process again and let it roll on overnight.

Thanks again.

It should not take hours. But if you leave an empty track behind when you cut and paste, you will hit the same bug I described where the time remaining will go on increasing, but the process will still complete normally in reasonable time if you let it run. You can delete an empty track by clicking the [X] button top left of the track.


Much thanks to all of you for the gracious help.

steve’s advice - Import audio from the MP4 files; Align the tracks end to end (Select all of the tracks with “Ctrl+A”; then “Tracks menu > Align > Align End to End”); Export.

worked well.