Novice seeking info on file compression (SOLVED)

Hi guys
Novice to Audacity - using the 2.0.2 exe version as an upgrade to an older version (1.3 I think). I couldn’t find anything close to my particular problem in searches but possibly using wrong keywords so apologies if it’s been covered previously.

I’d been using the latter happily to extract the sermons out of our church services and in doing so regularly got the file size to around 5 Mb. However since the upgrade (& without changing any settings) I can no longer do that. Where the service file might be in the order of say 15 Mb my extracted portion has, at times come out even larger, despite only being 20 mins out of a 75 min file. I’ve tried changing various settings in the options on extracting - putting the bit rate mode to Mono & dropping the quality right down from the previous 192 to 128, and everything in between.

The files are recorded on an TASCAM DR05, and then sent to me via email so all I do is just open them up, find the sermon section, delete everything else either side of it (again tried different ways of doing this which I didn’t have to worry about before e.g. cut/delete etc), then export the selection out as above.

The settings to the left of teh recording are: Mono 44100 Hz, 32 bit float (unsure if these are the same as I had previously).

I desperately need the file sizes to start coming out a LOT smaller than currently & have no ideas on what else to try, so hoping someone here might be patient & help me out?


If this is MP3 export then reducing the bit rate would reduce the file size.

However Audacity supplied by us doesn’t have a “Mono” bit rate mode (it’s something we are considering adding). So I suggest you uninstall your 2.0.2 and install 2.0.5 from Audacity ® | Download for Windows .

How long is the section you are exporting? Are you sure you are using Export Selection?


HAH - now there’s a thing :slight_smile:. Can’t remember but quite possibly not, rather just doing the Export which could indeed be precisely where the problem lies. Think I assumed if I’d deleted the content either side then the Export should work the same :frowning:.

Just tried another new file which was originally 34Mb & 35-1/2 mins long - Exported the selection of 14 mins with a BR of 96 & got a file of 10 Mb which I appreciate is good, BUT my point is that on whatever earlier version of Audacity I was using I was routinely getting file sizes under 6 Mb which would mostly have been 15-20 mins, & that’s what I’m really trying to achieve again if at all possible.

But yes they’re all MP3 files.

Has something changed over recent versions that mean perhaps file sizes are always going to be larger perhaps?

it’s not only “good” it is also “correct”.
If the bit rate is constant 96 kbps (96 kbps CBR) then that means that for every 1 second of audio there are 96 kbits of data.
14 minutes = 14 x 60 = 840 seconds.
840 seconds at 96 kbps = 80640 kbits
There are 8 bits to a byte, so that works out as 10080 kBytes, which is more or less 10 MB.

Assuming that is correct.
6 MB = 48 Mbits = (about) 48000 kb
20 minutes = 1200 seconds
so if there are 48000 kbits in 1200 seconds, there are 48000/1200 = 40 kbits per second (40 kbps).

Hmm - wonder if I’d have gone down quite that low on the BR but maybe so. At least I now have a better understanding of the ins & outs of what’s happening, as TBH before I was just playing around with little idea of what anything was doing :frowning:.

So THANK YOU hugely for taking the time to explain the basics to me - as I said I had done a good bit of reading yesterday but couldn’t find anything to explain how to get the file size smaller (because I was looking for the wrong thing!)

Ok - will have another go tomorrow & repeat some of the older files too so I can determine perhaps what settings I maybe did use before instead of making assumptions on things.

Will let you know the outcome :slight_smile: Much appreciated.

You were convinced not, so exporting more audio than you thought you were exporting was the only other possible explanation.

Yes if you have a single track, select some of it and CTRL + T to trim to just that selection, then File > Export Selection is not necessary because File > Export will ignore any white space between time zero and the selection. But if you leave even the shortest piece of audio in place before the selection you intend to keep, then File > Export will export the whole audio starting from that shortest piece.

There is a table here you might find easy to use: . Bit rate in kbps divided by 8 then multiply the result by 60 gives you the file size per minute in kB.


The fuzzy rules of thumb for MP3 compression are 32 absolute minimum for mono and 64 for Stereo. Below that most people still breathing can tell there’s something wrong. Above that, many people can’t tell.

If you have access to a Mac or iTunes for Windows, you can sometimes get a better compression in iTunes than we can do in Audacity. Apple supplies an actual Fraunhofer MP3 license.


If the sermons don’t contain music, just speech, you can half the sample rate to 22025Hz, which will reduce your file size.
This will lose all frequencies above 11KHz, but they aren’t necessary for comprehensible speech. Mono, rather than stereo, is sufficient for speech.

Are there any ABX tests supporting that claim?
I’ve tested many MP3 encoders and in my opinion LAME is, overall, one of, if not the best.

I think of the Fraunhofer encoder in a similar way to the Shure SM58 microphone. It’s old, hasn’t been updated in decades, but was for many years the “industry standard”. These days it is overpriced and probably no longer the best, but remains highly popular with professionals because they know it thoroughly and there are no hidden surprises. I believe that LAME is the only MP3 library that is still being developed.

Not for MP3, though - the sample rate does not affect the file size.


Though converting to mono does allow higher compression (lower “kbps”) for an equivalent sound quality.
A 64 kbps mono MP3 will have similar sound quality to a 128 kbps stereo MP3.
A 64 kbps MP3 will be roughly half the size of a 128 kbps MP3.

Sorry I was thinking WAV , a constant bit-rate mp3 isn’t going to be smaller by reducing the sample-rate :blush: ,
but as Steve mentioned above you can get away with a lower mp3 bit-rate when using a lower sample rate.
A variable bit-rate mp3 would be smaller by lowering the sample rate.

I dunno how widely acceptable Variable-Bit-Rate mp3 is though.

All modern MP3 players should be able to play VBR MP3, though some are unable to display the correct playing time or play position.

Some Podcasting services require CBR as do some audio book websites. For podcasts or audio books, assume CBR unless the service documentation explicitly says the VBR is allowed.

For music. VBR will generally give better sound quality than an equivalent sized CBR file.

Just wanted to return & close out this thread as all of your suggestions combined have enabled me to get my file sizes once again down to a more sensible volume.

Thanks to all of you who had patience & helped me work through the various options to get the solution.