CHAPTER 12: Digital Audio: Providing Aural Feedback for UI Designs Using SoundPool 457In this way, you can compare your MP3 (or any other codec file format) audio file sizes, and do
the simple math to figure out your percentage data footprint reduction, as we will do next for our
buttonaudio.mp3, or rather, our buttonaudio_320kbps_cbr.mp3 file (if you follow this naming
convention), that you generated by clicking the Save button. Data footprint optimization is hard
work, involving finding an optimal codec setting for each asset.
The buttonaudio.mp3 file size is 49KB, representing a 447% data footprint reduction. To figure this
out, 49KB divided by 219KB is 0.223744, which is 22% of the original, uncompressed file size.
100% minus 22% equals the 78% file size reduction. If you use the 1/x (inversion) key on your PC
calculator, you can get the percentage reduction, coming from the other direction. Inverting 0.223744
gives 4.469, which means that you reduced your file size by 4.469 times, which equates to a 447%
reduction. This is a fairly impressive data footprint reduction!
Now that we have seen that our MP3 file size is smaller than the Ogg Vorbis, let’s see how MPEG4
AAC in an M4A file format data compression improves your file size-to-quality ratio compared to
MPEG3. Since MPEG-4 is a more recent and advanced codec technology, it should provide us a
much better file size-to-quality ratio.
Exporting Lossy MPEG4 Format: M4A audio files
Follow the usual File ➤ Export work process to invoke the Audacity Export File dialog and select
the M4A (AAC) Files (FFmpeg) from the Save as type: drop-down menu selector. As usual, name
the file buttonaudio (which will be named buttonaudio.m4a by the Exporter after you click Save)
in the CH12 directory (or whatever your digital audio assets folder name is), and then click on
the Options button to open a Specify AAC Options dialog, as shown in Figure 12-12. I chose to
ratchet the Quality setting up to 500 to see what a resulting MPEG4 file size would be when using a
maximum quality level setting. Click Save to export the buttonaudio.m4a file.
Figure 12-11. Export an MP3 audio file named buttonaudio.mp3 with 320 kbps Constant Bit Rate Mode encoding