OS X Yosemite 10.10.4
Was using Audacity 2.1.0 and recently updated the version to the latest of 2.1.2
I am having difficulty with exporting multiple tracks for a particular WAV. It’s 16Bit 44.1kHz
What’s happening is that the mp3s that are exported come out at a lower bitrate then I had specified. Instead of what should be V0 mp3s, come out at (for example) 170kbps variable bit mp3s.
The reason for my alarm is that the the size is smaller and when I check the bitrate on my Win 8.1 machine it shows that bitrate that I did not specify. Usually a V0 mp3 is the length of minutes X 2 for the size of the V0 mp3, for example, a 4min song comes out 8 MB for the highest quality variable bitrate mp3. I’m now noticing this one particular WAV exports an mp3 at half the size (thus, ~4 MB).
Encoding, not ripping. I changed your subject title accordingly.
If you use variable bit rate you must accept there will not be a precise ratio between length of file and outcome bit rate, but that the outcome bit rate will depend on the material. If for example you export a mono speech track or a sine tone, that is easy to encode and the outcome overall bit rate will be far less than 220 kbps even choosing V0.
If you want to force a minimum bit rate with variable bit rate you will need to export using (external program) which calls LAME at the command-line. Use -b to specify the minimum. See http://lame.cvs.sourceforge.net/viewvc/lame/lame/USAGE.
As you are on Mac you will also have to find a LAME binary you can point the command to (the libmp3lame.dylib file offered on the Buanzo site can’t be used at the command-line). I have not tried them but I think the OS X LAME binaries on http://www.rarewares.org/mp3-lame-bundle.php would work.