There are entire horror movies that aren't as unnerving as the opening credits to John Carpenter's Halloween. What's so eerie, and sets the tone for a film that has become a revered horror classic and spawned too many better-left-unmentioned sequels, isn't the slow zoom into the firelit face of a menacingly grinning jack-o'-lantern. It's the insistent, jittery score, a simple piano melody repeating over a menacing drone.

Like the film itself, that memorable music is the work of John Carpenter, who composed the scores for many of his own films. His contributions include the pulsating electronic anthem for Escape From New York, the aptly swaggering synth-rock theme from Big Trouble in Little China, the lonesome harmonica howl of the sci-fi satire They Live, and the glossy, urgent throb of Assault on Precinct 13.

Carpenter, now 68, has slowed down in recent years on the filmmaking front. His last directorial effort was 2010's little-seen The Ward, which arrived after nearly a decade without a feature under his name.

"I was a moviemaking addict for many years," Carpenter said earlier this month from his home in L.A. "I just made one movie after another. I can't do that anymore. I'm too old now."

Carpenter's grumbled complaints about his age, which he repeated several times during our brief conversation, seem a bit disingenuous, considering that he's in the midst of a summerlong world tour - it will bring him Saturday to the Keswick Theatre - performing some of his synth-driven film scores, along with the music from his two recently released albums, Lost Themes and Lost Themes II.

Despite the title, the albums, recorded with his son Cody and godson Daniel Davies, consist of new music, not rejected scores from his films.

"I didn't make that up, my friend," Carpenter said of the Lost Themes title. "The record label thought it was a good way to sell more records. But they're not necessarily lost themes. They're lost in real movies, but they're not for real movies. They're for the movies in your head."

Now that he's taking his music on the road, Carpenter is free to conjure new images every night onstage, without the burden of having to fund, cast, shoot, and edit them. "I love playing music at this point in my life, and not playing it for a visual image, but playing it just for its own sake," Carpenter said. "All sorts of images come to mind when I'm doing it, and I think to myself, 'Oh, man, that would be pretty good.' But I was always a kid who could visualize movie scenes that didn't exist."

Carpenter is a lifelong film buff, famously a huge fan of the Hollywood Westerns whose plots he would borrow from in his horror and action movies. But he also grew up around music. His father was a music professor who played classical music around the house, though young John got more excited at the birth of rock-and-roll. "I'm old enough to have seen Elvis when he was on Ed Sullivan the first time," he recalled. He later directed Kurt Russell in a 1979 TV movie about the King.

Throughout his high school years in Bowling Green, Ky., and later in Los Angeles while studying film at USC, Carpenter developed a taste for live music when he played in a succession of cover bands, albeit in far-less-glamorous situations than he finds himself these days.

"We used to play for fraternity parties, so my experience in live performing was to stand there playing for drunken fraternity boys and their dates and watching them do the alligator."

He started scoring his own films out of necessity rather than a passion for music. "When you're a low-budget filmmaker, you don't really have any money to spend on a composer or an orchestra," he said. "You've got to rely on your own resources. A lot of movie directors or student filmmakers depend on records or preexisting music. But I decided - maybe arrogantly or stupidly - that I could, with a synthesizer, sound big enough and provide music that would be moody enough for a movie."

The film composers that Carpenter loved - he immediately cites Bernard Herrmann and Dimitri Tiomkin when prompted - were known for their sweeping symphonic scores. Lacking access to an orchestra, Carpenter turned to the synthesizer, creating memorable minimalist sound tracks that lend a stark tension to his films.

The same qualities mark his music on the Lost Themes albums, which could easily play under a scene of Snake Plissken reluctantly saving the world, or Michael Myers stalking unsuspecting teens. And they might yet, in the latter case. It was recently announced that Carpenter would return to his most-famous creation, executive producing the coming 10th sequel.

For now, though, the director suggests conjuring your own images to match his sounds. "Some night, go out in a car and drive around the city and put in one of the two Lost Themes albums," he said. "All of a sudden, you'll be in a movie."

John Carpenter: Live Retrospective, 8 p.m. Saturday at the , Keswick Theatre, 291 N. Keswick Ave., Glenside. Tickets: $29.50-$65. Information: 215-572-7650, keswicktheatre.com.