MP3 file size

[mdbk77]

I recorded a speech I gave into a Marantz recorder with settings: MP3-128 bit rate, Sample rate 44.1k

The talk lasted 1 hour and 20 minutes. The sound quality is excellent. The file size is 39.4MB.

I used Audacity to 1.2.6 to edit out about 10 minutes. Then I NORMALIZED it. Then I exported it to MP3 (using default settings, 128 bit rate).

The new MP3 file is now 72.4MB. Why did the size of the file jump? How can I avoid this?

Thanks for any insights!!!

Mike

[kozikowski]

I bet you think you cut your original MP3 file. You didn't. Audacity converts the work into a much larger internal production to get the tools to work, then you asked it to make a whole new MP3 file.

MP3 production is a cook, not a mathematician. Little bit of this, little bit of that. A good way to start a fight is the old "My MP3 encoder is a lot better than yours!" "Oh, no it's not!"

You're also staring at why WAV is a production format and MP3 is an Export format. They don't cross well at all.

The only neat, clean way out of this is to go back to the original MP3 file and use an editor that doesn't take it apart to cut it. Google your brains out, or do a forum search. This comes up periodically. Editors that do this trick have very limited palette, no special effects or noise reduction. Some allow you to fade. Some don't.

Koz

[steve]

I used Audacity to 1.2.6 to edit out about 10 minutes. Then I NORMALIZED it. Then I exported it to MP3 (using default settings, 128 bit rate).

The new MP3 file is now 72.4MB. Why did the size of the file jump? How can I avoid this?

My bet is that the original file was mono, but it imported into Audacity as a stereo track.
Alternatively it may have been encoded as "VBR joint stereo" and the Exported file as "CBR stereo", or something like that.
Perhaps the original was an MP3Pro file rather than a standard MP3?

The available options for MP3 export are quite limited in Audacity 1.2 - more flexible in Audacity 1.3. If you have a mono track in Audacity, then it should export as mono

As Koz hinted, each time you decode and re-encode an MP3 you loose a bit of sound quality. This is made worse each time it is done and the loss of sound quality cannot be recovered. Whenever possible you should use WAV files for editing, then encode to MP3 as the final step should an MP3 be required.

Have a look here: http://mp3gain.sourceforge.net/

[mdbk77]

Many thanks, Koz and Steve! You are both correct!!

I didn't understand MP3s AND the original was Mono.

But if the original is Mono, then why did it play in both speakers? Apparently because no one would ever want a single speaker MP3, so all players (or audacity) split the sound into two speakers upon playback???

When I opened the file in Audacity I was not prompted for mono or stereo. And when I delete either the left or the right channel in Audacity, it deletes the other as well. If I choose the mono setting in Audacity (top left) and export to mp3 the file is still 72MB.

I would like to keep it in mono (to keep size down), but of course would like listeners to hear the edited file from both speakers. Is this easily doable with Audacity? If not, I will either use the larger file or google for an mp3 editor that doesn't take the mp3 apart.

In the future I will record in wav

Any addition insight is appreciated, and already, THANKS A MILLION!!

Mike

[waxcylinder]

You can work on your mono file in Audacity and keep it in mono for export by setting Audaicity preferences - use Edit > Preferences > Audio I/O and select Channels: 1 (mono)

WC

[mdbk77]

Thanks, WC, but Mono was already the setting, so it doesn't seem to make a difference.

Mike

[kozikowski]

<<<Mono was already the setting>>>

Restart Audacity. Some of the Preference settings don't stick until you restart.

Koz

[mdbk77]

Thanks, Koz! It didn't make a difference. I'm thinking I'll just use the larger file this time, and record as wav next time

[steve]

But if the original is Mono, then why did it play in both speakers?

in a stereo file you have 2 audio "channels". One channel is set to play through only the Left output (left speaker/headphone) and the other set to play only through the right. (It can sometimes be a little more complex than that with MP3s and other compressed audio files, but let's not worry about that just now).

With a "mono" recording, there are 2 ways that it can be represented. For audio files, "mono" usually means just a single audio channel that is set neither to Left or Right, but is set as "mono". When you Import this type of mono file into a new empty Audacity project, Audacity should show it as a track with just one channel. If you open Audacity and use one of the "Generate" functions (Generate menu), then Audacity creates just such a mono track, and if you click on the name of the track you will see in the drop down menu that it is set to "mono".

Now I said that there are 2 ways to represent mono audio. The other way is as 2 identical channels, such that there is a Left channel that is identical to the Right channel. If you listen to a radio that is tuned to a station on "long wave" (AM radio), then the audio is mono. It is transmitted as a single audio channel, but when you listen to it, you are listening with 2 ears, so your brain is receiving 2 channels (left ear and right ear) and if you listen through headphones you will notice the strange effect of the sound being in the middle of your head.

If you play a single channel audio file in a media player, because it is not specified as being Right or Left, the media player should simply play the file through both speakers.

Here's a little experiment to try that should demonstrate this practically - this is bet if you listen through headphones.
1) Open Audacity
2) From the Generate menu, generate a tone.
3) Play the tone, and if you are listening through headphones and everything is set up correctly, the tone should sound like it is in the middle of your head.
4) Click on the track name and in the drop down menu you will see that it is set to "Mono".
5) Now, from the drop down menu, set the track to "Left channel" and listen to it again. You should hear that it plays only through the left headphone (if it plays through the right headphone, you have your headphones the wrong way round).
6) Now press Ctrl+D (this will duplicate the track).
7) Click on the name of the duplicate track and set it to "Right channel".
8) If you play this again, it should sound just the same as the original mono track.
9) Use the "Solo" button on the tracks so that you can listen to one, then the other track. You will hear that one track plays to the left ear and the other plays to the right, but when both tracks are enabled you can hear it through both and it sounds mono. The original single channel mono track played identically through both left and right, and our new identical pair also plays identically through both left and right.

Earlier I said that Audacity should import a mono file as a single channel track. I have noticed that in some situations it doesn't. I'm not quite sure why it doesn't and it should not really do this, but with some files on some machines I have seen it happen. What it does instead is to import it as 2 identical channels - a stereo track with both left and right the same. In Audacity 1.3 it is very easy to correct this (I think this is slightly different in Audacity 1.2). You simply select "Stereo Track to Mono" from the "Tracks" menu and it mixes the two tracks into a single channel mono track.

If you then Export the mono track as an MP3 file, it should export it as a single channel mono track and enable you to increase the compression settings to get a smaller file. However, things can go wrong here as the encoding is not done by Audacity, it is done by LAME, and depending on exactly which version of Lame is being used, you can get incorrect settings. Personally, if the encoding settings are important to me, I prefer to Export as a WAV file, then use LameDropXPd to encode the file. LameDropXPd is a very good (free) MP3 encoder that also uses Lame, but because it is specifically an MP3 encoder program, it is more flexible and easier to specify exactly what compression settings you want. There are plenty of other excellent free stand-alone MP3 encoders that have advantages over the basic settings that are available in Audacity 1.2. MP3 encoding in Audacity 1.3.7 is better than in 1.2 and offers more options (such as VBR).

[mdbk77]

WOW! That is a lot for a rookie like me!! But I will work through it next go round.

It is stunning quality of help you all have offered... it is humbling.

Many thanks (seems hardly enough). And thanks in advance from those who will hopefully benefit in the future from this thread!!!

Mike