When creating MP3 files of your audio projects there are various options for MP3 export that you need to consider. There is no one-size-fits-all settings that is best in all situations. But armed with the following information, you can make the decisions between an appropriate quality and size of file.
Though I use Audacity, the following information is general enough to be used with various sound editing programs. The parts that are specific to Audacity are just the steps you go through to find these settings. If you are not using Audacity, you can probably figure out where these settings are in your own editor.
This is not intended to be the final authority on the subject; especially since so much of this is subjective to your own ears and opinions. This is simply intended to give you a basic understanding of what should be considered in creating MP3 files that are being distributed to your supporting churches or used for podcasting.
Export MP3 in Audacity
Once you have your sound file edited and the project is saved (so you can go back and make changes), you are ready to export an MP3. Go to Export in the File menu. Choose MP3 Files in the Save as type: drop-down menu. Then choose Options.
Bit Rate Mode
The different bit rate options can give you smaller file sizes, but at the cost of potential compatibility and quality issues. I always choose Constant (also called CBR in some editing software) on this option regardless of the project I am working on. This gives the largest file size for compatible settings of the various options, but also gives me more confidence in the compatibility of the final file. The tradeoff is that the sound quality (especially with music) may not be as good as some of the other options.
What do I mean by the most compatible of the bit rate options? Particularly when streaming your audio file online (like an audio prayer letter) you will experience fewer problems with in-browser audio software by using constant bit rate. CBR files will not stutter like the other bit-rate options have a tendency to do. Constant bit rate will also be more accurate in reporting the length of the audio file in a person’s browser or MP3 player. While not as much of a problem any more, variable bit rates (all three of the other options) sometimes would not play in some MP3 players.
But the constant bit rate does have its trade offs. The biggest being that of the various bit-rate encoding methods, constant bit rate is about twice the final file size in MB as the other options of similar quality levels. If our whole point of making MP3s is for generating smaller file sizes, then we could actually do better by using a variable bit-rate setting.
The second downside is that constant bit rate may not have as high of audio quality as a variable bit rate file of similar quality settings. Because I only deal in spoken word (no music) in my audio recordings, this is not much of an issue. However, if you compare the audio quality of two music files that are encoded with constant bit rate and variable bit rate—especially at a quality setting that is towards the lower end—you will probably hear a significant difference in the quality. And, surprisingly, the smaller, variable bit-rate file will be the better quality.
At some point I think the compatibility issue will be a thing of the past. If you are dealing with a relatively small audience for your audio files, you may be able to deal with any requests for a differently encoded file to be sent to someone. At this point though, some organizations dealing with large numbers of listeners are still using constant bit rate to cut down on support requests.
Regardless of what you choose in the previous section, the actual bit rate that you choose in the Quality drop-down menu is where you can end up with a really small file or a good high-quality MP3—but you can’t have both. There has to be a compromise and balance between these two options to get the sound quality you want.
It depends on the project and the type of sound I’ve recorded that determines what I choose in this section. For a podcast that is is just spoken word with no music, I usually choose 96 kbps. You can probably go a bit lower before you start to hear sound quality issues. Much higher than that and you won’t be able to tell a quality difference in the spoken audio.
If, however, I am doing audio that will go into a video file–which I do for my video podcast–and I know that the MP3 will get re-encoded later with the video, then I will choose a higher sound quality. Usually I do these at 192 kbps. The sound quality doesn’t have to be perfect and I am also working with spoken word only, no music. If I wanted to make sure my sound was the best quality it could be for my video project (or if I were using music) then I would choose 320 kbps or export a WAV file.
For anything with music, then the lowest you probably want to go is 128 kbps if the music is background or ancillary and is not the focus of the sound file. If you are trying to show the quality of the music then you should choose 256 or 320 kbps for the best quality MP3 you can get.
This setting is only available if you are choosing Preset or Variable in the Bit Rate Mode section. This determines whether your encoding will be done quickly or with the best quality. Since this only affects how quickly the file will be encoded, there is no reason to not choose Standard. It may take a few minutes longer to encode, but will result in the best possible file based on your other settings.
The two options are Joint Stereo and Stereo. They are both stereo options, but where the two channels (left and right) have the same sound, the encoder joins them together using the Joint Stereo option. This results in a slightly smaller file size.
I have no reason to record stereo for most of what I do (spoken word). Therefore, I make all my sound files within Audacity into mono files. I do this even if I have multiple tracks or channels. Then when I encode my MP3s I choose Joint Stereo in the channel mode which results in a smaller file.
Even when I do interviews and have two or more people talking, I do not separate them into left and right stereo. There is no practical advantage to this separation and it allows someone who only has hearing in one ear to be able to fully enjoy the interview. Since I work with the Deaf, this is something that I tend to think about more than most people. If you choose to separate your interview participants, you should still only slightly separate the left and right channels so that someone listening with one ear bud can understand both sides of the conversation.
After you get your settings the way you want, then save your file by giving it a filename. When you click the Save button another screen will pop up. It says Edit Metadata at the top of the screen. This is where you can fill in the information that is shown in MP3 players, iTunes, Windows Media Player, etc. This is called the ID3 tags of an MP3 file. However, I have never been pleased with the results of the ID3 tagging in Audacity.
There are great ID3 tagging software available for the various platforms you can use. Many people just use iTunes on Windows and Mac to create the ID3 tags. I have always used a program in Linux called EasyTAG. There is also a Windows version of it, but you have to install the GTK+ engine. Typical of Linux programs, EasyTAG couldn’t be much more ugly than it is, but also it couldn’t be more powerful. There are so many features and time saving features built into the program that you would have to be a rocket scientist to take advantage of all it has to offer. Fortunately, if you want to create proper ID3 tags you can also use the fairly intuitive interface to work on one file at a time.
I have heard podcasters talk about some other programs, but I have no personal experience with them. For Windows there is MP3 Tag and ID3 Editor. The recommended programs for Mac are ID3 Editor and iTunes.
Go Make Some Noise!
That should get you well on your way to properly exporting MP3 files that are useable for distribution. You can use these files for podcasts or for emailing field updates to your supporting churches. If you record your services you can put several week’s worth of sermons on one CD or DVD.
With all of this I recommend you save your Audacity project and export a WAV file that you can archive. Fortunately there are no settings for WAV files like there are for MP3 files. The WAV file is a lossless file format. That means that all of the information possible is in the file; whereas, MP3 files have to throw out information in order to make the file size smaller. If you ever need to edit your file to mix in music or to cut the file into a soundbite, using the WAV version of the file will result in a better quality final product. If you re-edit an MP3 then you are taking a file that, by nature, is lacking sound information and throwing out even more when you compress it into MP3 again.
[The Audacity website has a page that explains each of these settings.]