Apple has confirmed it will be holding a major event in San Francisco on Tuesday September 9th, with the announcement expected to feature the new iPod nano 4G. It’s traditional for Apple to announce fresh iPod models just in time for the Fall and Holiday shopping seasons, and speculation has been rife as to how the nano might evolve.

iPod nano 4G

An obvious and likely improvement is more capacity. Flash memory prices have dropped since Apple’s last refresh, and the existing 4GB and 8GB capacities will probably be joined by at least a 16GB nano. It’s also possible that Apple will reduce the price of their lowest-capacity iPod nano 4G, in an attempt to create a tempting upgrade for iPod shuffle owners and maintain the pressure on rival PMPs.

The form factor of the iPod nano 4G also looks set for a change. Photos and dimension diagrams purporting to be the upcoming nano have leaked, suggesting that Apple will return to the long & thin style of the 1G and 2G models. Although this would make for a longer casing than the stubby iPod nano 3G, the extra length would accomodate a deeper display that, when held horizontally, would be better for widescreen video. Given that Apple is already supplying widescreen-format content through iTunes for the iPod touch and iPhone, it makes sense that they would rework their mainstream PMP to take advantage.

Following the more curved profile of the iPhone 3G and the speculated iPod touch 2G, the iPod nano 4G is believed to have a curved, oval-profile casing. It’s presumed that this would be metal, with a straight plastic or glass screen cover inset into the fascia so as to minimize reflections. The exact resolution of the screen is unknown, but Apple is likely to pick a similar pixel density to that of the iPod touch if decent video performance is its new goal.

While Apple has not commented on the leaked dimensions, they do match those used by case manufacturer XSKN in their EXO mask N4 range. They’re given as 90.75mm tall by 38.75mm wide by 6.08mm deep, which would make the iPod nano 4G the thinnest and narrowest iPod nano so far.

SlashGear will be Live Blogging the September 9th Apple announcement, so check out http://live.slashgear.com/ at 10am EST for the full details!