Audacity Forum

Whenever I try to combine one part of an mp3, which I cut beforehand, and paste it at the end I always hear a quick and abrupt stop right before the cut & pasted part.

For example in this mp3 which stevethefiddle generously posted: http://www.sendspace.com/file/vwe7tk

At 1:08, a cut part of the mp3 was pasted there at 1:08, but it has been combined in a way that it flows so smoothly that you couldn't notice it.

How does someone do something like that?

I think there's something about MP3 files have fixed sizes, the music isn't continuous although it sounds like it. This makes editing rough because if you don't happen to hit one of the music boundaries, you can't edit. There may also be a problem in trying to edit two different MP3 files, one high quality and one not.

MP3 is a delivery format. WAV is an editing format.

Koz

kozikowski wrote:I think there's something about MP3 files have fixed sizes, the music isn't continuous although it sounds like it. This makes editing rough because if you don't happen to hit one of the music boundaries, you can't edit. There may also be a problem in trying to edit two different MP3 files, one high quality and one not.

MP3 is a delivery format. WAV is an editing format.

Koz

So do I need to convert the mp3 to WAV?

Is there a particular way in which stevethefiddle was able to blend a cut part of the mp3 at 1:08 into the rest of the mp3 so smoothly?

Carcinophobe wrote:So do I need to convert the mp3 to WAV?

When you import any audio into Audacity (MP3, WAV, Flac... any format supported by Audacity), it is converted to uncompressed audio data suitable for editing.

The source files that you import into Audacity should ideally be WAV format. WAV is an uncompressed format and does not "damage" the sound quality. MP3's do a couple of unpleasant things to recordings - 1) they throw away some of the audio data, and thus lower the sound quality (this is not repairable) and 2) MP3's add a little bit of silence just before the start of the file.
For these reasons, you should wherever possible use WAV format throughout the production process.

As Koz has said, MP3 is a "delivery format". If you want to send an audio file electronically (e-mail, PodCast, Web download...) WAV files are BIG. MP3s are very much smaller, and so long as you only compress the audio (your finished production) to MP3 once, the loss of sound quality should not be too noticeable (use at least 64kbps for mono and at least 128kbps for stereo files - better quality is achieved using bigger numbers).

Carcinophobe wrote:it has been combined in a way that it flows so smoothly that you couldn't notice it.
How does someone do something like that?

He's had lots of practice

There are good places and bad places to make your edit point - An ideal place for strongly rhythmic music like this is immediately before a beat, and as close to the centre line (0.0 on the vertical scale - this is known as a "zero crossing point").

Here is an example of a good edit position:
And zoomin in very close we can see that it is very close to a zero crossing point:
Sometimes it is not possible to meet these conditions, in which case you would use a cross-fade like this:
For the cross-fade I have overlapped the tracks to be joined, and in the region of the overlap I have applied a "fade out" effect to the upper track, and a "fade in" effect to the lower track.

(all of the edits shown above sound "seamless").