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Optimizing MP3 exporting in Audacity

I've been messing more and more with the settings in Audacity, specifically towards tweaking audio settings so that my  produced podcasts will sound great and not take forever to work on.  With the LAME MP3 Encoder Library that you'll need to download to export your files as podcastable MP3s, it's a snap, but the default settings don't always produce the friendliest files.  Here are some tips.

Optimally, you'll want to achieve 3 main goals when producing your podcasts, regardless of what audio editing program you happen to be using:
  • Have great-sounding content
  • Have the generated file size of the resultant MP3 be as small as possible, to reduce bandwidth and data transfer concerns, and generally be better for users to store on their PCs, iPods, iRivers, or other digital media.
  • Have your MP3 file export quickly once you're done recording/editing your show, so that you won't be waiting forever while it renders (this isn't expliticly required, but if you either podcast frequently enough that people expect your show to be available by a certain time, or you just need to export and get on with your life, it can be a concern).
For the first point, you need only invest in a good microphone.  But don't think you need to drop $400 on studio-quality equipment - I get by with great recording by using a $20 Plantronics headset mic I bought at a local shop. 

Secondly, to get the filesize shrunk down to a manageable level, you'll need to modify Audacity's default settings by tweaking the bit rate at which Audacity saves your recording to an MP3.  To do this, click on File and then select Preferences (Ctrl+P).  Then, from the "File Formats" folder tab, reduce the Bit Rate setting from its default setting of 128K in the MP3 Export Setup group.  128K is near CD quality, but results in larger file sizes (about a MB per minute of audio).  Even for podcasts that feature music, I've found using a bit rate of 64K works great, resulting in about half the size (makes sense, 64 being exactly half of 128).  Note that reducing the bit rate shrinks the filesize by applying compression to the file, and so takes more work and results in longer exporting time for rendering.  But that's our next point...

Lastly, to speed up the rate at which Audacity will actually export your recording to an MP3, you can save the recording in mono (as opposed to stereo).  This doesn't degrade the quality level as much as you might think, because you're reducing the number of channels carrying audio in half, and balancing it between the right and left speaker for a nice mix.  So make sure in Audacity's Preferences window on the "Audio I/O" tab (or "Digital I/O" on some versions), that the Channels drop-down menu is set to "Mono" in the Recording group.  Again, this forces Audacity to do half of the work, only needing to render half of the content. 

But there's one more thing to get your podcasts to export quickly: for those of you who import clips (sound effects, promos, songs, etc.):  you can save additional rendering time by making sure the clips are mono tracks before rendering starts.  Often, when external sounds are imported, they come in as stereo (two-channel) tracks, and are displayed as such.  If you're going to be exporting your podcast MP3 file as mono, there's no reason to keep a track in stereo, so left-click on the track's title, and then select "Split Stereo Track".  This creates two tracks for that clip - one for each channel.  Click on the "X" on the second track to delete it from the timeline, and then click on the title for the clip's remaining track, and then select "Mono".  Having all your tracks in the same format reduces Audacity's need to convert/upscale/downscale tracks, and do less work overall - resulting in faster exporting so you can get your content out to the world faster.

Happy podcasting!
Posted: May 26 2005, 10:57 AM by guam-aspdev | with 17 comment(s)
Filed under:


Rich said:

Thanks Jason, great advice and well explained. Cheers!

# June 6, 2007 1:03 PM

DrSlony said:

" If you're going to be exporting your podcast MP3 file as mono, there's no reason to keep a track in stereo, so left-click on the track's title, and then select "Split Stereo Track".  This creates two tracks for that clip - one for each channel.  Click on the "X" on the second track to delete it from the timeline, and then click on the title for the clip's remaining track, and

then select "Mono"."

Incorrect. This will just throw out a channel of audio along with all the instruments and sounds that were on it as well.

Say the vocalist is in the center (ie. both left and right channels have the same voice data), guitars dominate the left channel and violins the right. If you do what was written in the article above, you lose either violins or guitars depending on which channel you delete.

The proper way to do this is to just click on Tracks > Stereo to Mono. This way you get retain all instruments/sounds.

# September 2, 2007 10:02 PM

Audio kid said:

He's recording from a mike Dr Slony - that's mono.

# June 26, 2008 6:45 AM

Simon WIld said:

This is so hot, I really love it.

mmmm yeah

# October 15, 2008 7:29 AM

Simon Wild said:

This text turns me on!

# October 15, 2008 7:32 AM

Dave Penny said:

I compressed to 61kb! I am so turned on now

# October 15, 2008 7:56 AM

Dude Lebowsky said:

Ha ha wtf are you guys talking about?

# July 29, 2009 10:21 AM

name said:

bring that times back!,

# August 25, 2010 4:58 AM

Andrew said:

Hey great post. Thanks for sharing this info. I'm working on shrinking some audio files and wasn't sure all the best ways to do it. Really helpful...

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