iTunes 9.1 was released the other day, and one of the many improvements it offers is one found in the preferences for iPods and iPhones: Convert higher bit rate songs to 128kbps AAC. You can find this on the summary page of your iPhone/iPod. It used to only be available for iPod Shuffle, but is now available for other iPod models — and I’m assuming, the iPad, too.

Songs that you purchase from iTunes and Amazon come in a high-quality, close-to-CD-sounding bit rate: 256kbps. That’s roughly 32KB per second, or 2MB per minute. An album of 60 minutes, therefore, would be around 120MB.

However, my iPhone, even at 32GB, still cannot hold my entire music library. One solution I tried was re-encoding some of my higher bit rate albums at 128kbps, which to my ears sounds great for the majority of my music. The problem is that I now have two versions of the albums floating around in my iTunes library, doubling the space on my hard drive.

What this new feature does is encodes a 128kbps version to your iPhone/iPod directly instead of keeping both the higher bit rate versions as well as the lower bit rate versions in iTunes. In other words, keep your 256kbps in your iTunes library, and only have 128kbps versions on your iPhone/iPod.

After selecting this little checkbox, I managed to squeeze out around 2GB of space, and it cost me nothing but a long wait. Be prepared: if you have a lot of music at higher bit rates, this can take some time. It took me nearly three hours to convert 850 songs on my 2GHz MacBook.

Anyway. Nerdery done. Try it out if you wanna free up some space.