Primus are just one of the teenager-friendly ’90s acts to be revived in Nick Catchdubs and Mr. Ducker’s Radio Friendly Unit Shifter mixtape

The free, legal online music released in the last few months has had a distinctly nostalgic bent to it, reaching back both to the summer that was and to a bygone decade. August’s offerings also finally forced Radio Silence to cave in and offer the highly researched, incredibly influential presidential endorsement so many readers haven’t been clamouring for.

Nick Catchdubs and Mr. Ducker — Mishka Presents Radio Friendly Unit Shifter (www.zshare.net/download/18038220d7aeb70d/)

If the 20-year cultural loop holds true, those grungy and post-grungy sounds of the ’90s will make a major comeback in a few years. In fact, astute listeners have probably already noticed drop-D tunings and smelly flannel starting to steal attention from kitschy ’80s synth bleats. Nick Catchdubs and Mr. Ducker’s mix, Radio Friendly Unit Shifter, is almost enough to make the impending return of all things ’90s not seem like a dreadful possibility. And to be clear, it is a dreadful possibility.

Essentially, the mix is a gigantic, hour-long melting pot of music that made 15-year-old boys excited 15 years ago, from Rage Against the Machine to Folk Implosion to Cibo Mato, Primus and Everclear. Though it might not take much talent or bargain bin-digging to compile a mix of old hits, Catchdubs and Ducker undeniably produce huge grins throughout. At the very least, Radio Friendly Unit Shifter serves as an important reminder to anyone who might have forgotten that Harvey Danger’s “Flagpole Sitta” and Rancid’s “Roots Radicals” are completely awesome, while Porno for Pyros’ “Tahitian Moon” and Temple of the Dog’s “Hunger Strike” are kind of crap.

alpha. — The FIXtape (www.zshare.net/download/174784731530fffc/)

This month’s obligatory hip hop mix tape mention goes to the annoyingly named Indianapolis emcee alpha. (not to be confused with the British trip hop group Alpha) and his (also annoyingly named) album the FIXtape. Fortunately, alpha. makes up for his troubles with punctuation and capitalization with a thoroughly enjoyable album filled with bizarre beats and engaging rhymes. One of the FIXtape’s most distinguished characteristics is its often detached, spectral production, which lends the often politically charged lyrics extra weight.

Considering that the American presidential election is finally ramping into high gear — and that John McCain received a mention in last month’s Radio Silence — it should also be mentioned that the FIXtape includes a surprisingly listenable rapped biography of Democratic hopeful Barack Obama. Yes, picking which candidate you want to win the presidency based on the amount of quality, positive hip hop songs they influence is completely acceptable.

Air France – Rooftop Music (69.90.113.100/podcast/2008/246.mp3)

Air France’s Rooftop Music mix would have been better if it came out in mid-June instead of late August, but it’s definitely worth a listen. As the name suggests, the mix is ideal for sitting out on a patio — or rooftop if you’re lucky enough to find one — with a cool cocktail on a perfectly breezy summer night. The mix features the chic, chill sounds of Quiet Village, St. Etienne and Hugo Montenegro, among others. With any luck, there will be a few more nights this year where it can be used to its full potential.