Each week Ross Rubin contributes Switched On, a column about technology, multimedia, and digital entertainment:

The iPod and iTunes haven't ostensibly suffered for (and have arguably gained from the) lack of a subscription music service. However, while such services have proven a tough sell to consumers at large, they have their benefits. One is the general liberation from the 30-second sample, a tiny prison of time that makes it difficult to engage in meaningful music discovery, the silver lining in the digital cloud that has been raining on the music industry for so many years.

In contrast to Rhapsody, Napster and Microsoft's Zune Pass, which offer several ways within their software for subscribers to hear full tracks in which they might be interested, Apple has recently turned "out of band" for music discovery. The high-profile announcement with Starbucks at the introduction of Apple's latest round of iPods brings the portable devices to where the free music is rather than vice versa. Among Apple's portable music players, the automatic track identification works only with the iPod touch and the iPhone. However, the flat-panel televisions in New York City Starbucks locations also note PCs and Macs as suitable (and prevalent) clients for purchasing music played at the popular coffee retailer.

An encouraging aspect of the collaboration between Starbucks and Apple is that the right company is making the brown product. However, one hot spot of trouble brewing in this Half-n-Half is that one can listen to the music only at a Starbucks location. This begs whether Apple would continue such a partnership when the iPhone finally gets access to 3G (perhaps to the scandalous exclusion of AT&T) or whether it or another device such as the iPod touch embrace WiMAX. But extending access to Starbucks' percolated playlists need not wait for such wireless advances. The two companies could enable access via a simple option in iTunes that would stream Starbucks' Hear Music XM station -- or an equivalent -- via any broadband connection.

This is why Apple's other recent music-discovery announcement is in many ways the more important one. Apple has teamed with iBiquity, the developer of HD Radio, and the nation's largest radio broadcasters that transmit Top 40 hits and absolutely no government brain control signals to domestic radios everywhere, to enable tagging of songs on select HD Radio-capable receivers. There could be a number of ways that such tags make their way back to iTunes.

This represents a significant turnabout from the early iPod days in which Apple used the entire 30-second Ataris punk song, "The Radio Still Sucks" in one of the commercials for the device. We are still in the early days of HD Radio, but it is the heir apparent to AM and FM. And while its receivers are too power-hungry to embed in a portable player today, the agreement could portend support for HD Radio in future iPods, or at least add-ons such as the FM radio attachments Apple, Griffin Technology, and others have offered.

The Starbucks and HD Radio music discovery partnerships dispense with the time and money requirements of competitors. In contrast, services such as Napster or Rhapsody must get users to pay attention to ensure that they will continue to pay money. There is too much labor to find music you love. On the other hand, while even subscription services have limited libraries, they are vast compared to the eclectic smattering of music played at Starbucks and the wider but generally mainstream selection of music played on popular radio stations.

A passive radio-like discovery strategy, while a step forward for Apple to compete against the full track selections available on subscription services, can offer only serendipitous discovery. The challenge for those offering full-track listening -- even for lala.com which plans to offer it for free -- remains navigating consumers around a large catalog in the most efficient and effective way possible.