If you keep up with Apple developments at all you probably already know that today is the one year anniversary of the iTunes Music Store. In honor of that Apple released iTunes 4.5 and Quicktime 6.5.1.
The new version of iTunes includes features like the Party Shuffle, Jewel Case Insert Printing, and iMix. You can read about all that stuff over at Apple’s site or pretty much any other Mac news website.
The feature that I found most intriguing is the new Apple Lossless Audio Codec that comes with Quicktime. MP3s and AACs have revolutionized how we think about music. But let’s face it, they are compressed audio files. Any CD will sound better. iTunes and the iPod will quite happily play uncompressed AIFF files but they are much larger. You are probably familiar with an MP3 at 128 kbps. An uncompressed AIFF file runs at 1411 kbps. In other words, 0.94 MB per minute versus 10.33 MB per minute.
So I pulled out my CD of Jet’s “Get Born” and decided to do a little experimenting with “Are You Gonna Be My Girl.” Marc Heijligers did some excellent qualitative studies of various types of audio compression in “Encoding Observations.” I used a method similar to his to analyze Apple’s Lossless compression.
I used Peak to rip an uncompressed AIFF of the track. I opened that file with Quicktime Player Pro and exported it to a movie with the Lossless codec. (Unless I missed something, it seems that only the “export to Quicktime Movie” option allows you to use that codec.)
Just to be completely legit, I exported another movie with the audio uncompressed. The first thing I noticed was the difference in file size. At 3:33 long, “Are You Gonna Be My Girl” was 36.1 MB uncompressed and 27.1 MB with the lossless compression. The compressed file was 25% smaller. Again in comparison, a 128 kbps MP3 is 91% smaller. For this song it would be about 3.3 MB
Obviously an MP3 or AAC is a lot smaller, but you also lose some of the sound information in the process. This new Apple Lossless codec promises to save 25% in file size and is supposed to sound exactly the same. To test this out I opened both the uncompressed movie and the lossless movie in Peak.
Visually the two files seemed to have identical waveforms.
Lossless Compressed Audio
With a quick listen on my studio headphones, I couldn’t tell the difference. I needed to be sure though that there was literally no difference. This is where I used a method that Marc talked about in his article.
I inverted the phase of the Lossless compression file.
Then I copied the entire file to the clipboard, and using Peak’s “Add” DSP function, I mixed the phase inverted Lossless audio with the original uncompressed audio.
The resulting audio file was completely silent.
A sound waveform looks a squiggly line drawn along the X-axis of an X/Y graph. You might be familiar with a Sine wave from trigonometry. A simple tone looks like that. When a sound is phase inverted, the peaks and valleys of that squiggle are swapped. So where the original sound might have a peak at 4 on the Y-axis, the inverted sound would have a valley at the same point in time at -4 on the Y-axis. Obviously if you add 4 and -4 you get zero. So a phase inverted sound mixed into the original sound should give you a silent audio file.
Since I phase inverted the compressed file, mixed it in with the uncompressed file, and wound up with a silent file, the codec truly is lossless. The two files are sonically identical.
Out of curiosity, I imported the original AIFF file into iTunes. I went into the preferences and changed my import settings to “Apple Lossless Encoder.”
Then I used the “Convert” function under the Advanced menu to convert my AIFF into a compressed file using the new Lossless codec.
The resulting file was an AAC file with the same .m4a extension as my other AACs. When I got info on the new AAC, I found that it was 1061 kbps.
Lossless Compressed Audio
With a space savings of 25% and truly no loss of sound quality, Apple’s new codec is definitely something to take a look at for both sound professionals and audiophile consumers.