I'm traveling north on the 15 freeway in a small car with a drummer and a trumpet player. It gets dark early this time of year, and the premature evening has come with fog. We proceed at a snail's pace.

Talk turns to a jazz jam in Little Italy at the Spaghetteria, and some of the young lions that show up there, and the trumpet player -- his name is Bruce Cameron -- says this: "jazz musicians are smart. We're supposed to be good at math. I could do statistics and geometry, but not algebra." He laughs. "Maybe that's why my career has been such a letdown." He laughs again.

And now the drummer -- his name is Kirk Hoffman -- he laughs too, which is good because earlier in the day, the Lenox Lounge, an old-school Harlem jazz nightclub with a long pedigree announced plans to throw in the towel.

And in a few more hours Dave Brubeck will pass, just one day and eight years shy of a full century. This will be marked as a huge loss to jazz in general.

But tonight? Tonight is a good night for jazz. We're headed up to a private jam session in the Blue Room.

The jam session is vital to virtually all forms of music in which free expression is not only encouraged but the norm; classical musicians not so much, but folk, punk, rock, blues, and especially jazz musicians all meet up for regular jam sessions. In jazz, there are two types of jam session: public, and private.

Jazz clubs in years past have made much hay of the public jam session, especially through the golden era of jazz and on into the '50s, the '60s, and the '70s.

As Wiki-defined: "A jam session is a musical act where musicians play by improvising without extensive preparation or predefined arrangements. Jam sessions are often used by musicians to develop new material, find suitable arrangements, or simply as a social gathering and communal practice session."

Patience Higgens, a New York tenor saxist ran the jam at the aforementioned Lenox Lounge for years. It started late in the evening in order to accommodate players who had landed steady work on Broadway. As the shows would close for the evening, jazzers among them would make their way to Harlem and take their turns playing with Higgens' group.

Quite often, public jams are opportunities to see luminaries drop in and work out with whoever else is there. A public jam is quite often a revolving cast of players where order is maintained by means of a sign-up sheet. When it is one's turn to play, sheet music is exchanged, a song or two performed, and the next player in line is called up.

In San Diego, Gilbert Castellanos, Ben Wanicur, Reka Parker, and Mark Augustine host some of the better-known public jams.

The private jam is a different animal entirely.

"I like everything except for the part where you do all that note-playing," a girlfriend once said of my jazz performance. "That's where I tune out." Why? "It gets boring. Totally."

From Le Jazz at Stanfor.edu: "The secret to jazz, of course, is improvisation. Against most non-jazz listener's conception, improvising doesn't mean playing whatever you want. To improvise is to take the melody and changes (harmony) and stretch and embellish them so you still have the same piece, but you're not just playing the same damn thing over and over and over, like in most pop songs."

But no matter. And in fact, my girlfriend of old was not alone. When smooth jazz came along, it found a lively audience of like-minded types who dug the jazz ethic but disliked all that improvising. Nary a complex solo to be found in a smooth jazz song, even though the genre became a real money maker for straight-ahead jazz artists who were willing to have their wings clipped for the sake of a larger paycheck.

Smooth jazz progenitor David Sanborn, for example, on alto sax can noodle with the best of them. That he rarely does is about form over function: smooth jazz does not tolerate long-winded sonic exploration. I wonder if Smooth Jazz musicians have given up the art of the jam as well.

"A private jam has the qualities of both a rehearsal and a live performance. But it is also like going to the gym for a workout," sax man Bill Shreeve explains later in an email. "Jazz improvisation is all about musical communication and interaction between players. Whereas we all practice by ourselves to work on our skill set, it’s important to play with other musicians to develop real world musical interaction skills. Great jazz improvisation is about action, reaction and chain reaction."

Shreeve's tenor gleams like old gold in the Blue Room, but his alto sax looks as if it came from a salvage yard. The best ones often do.

"In our [private] jam," he says, "we take turns selecting songs and frequently wind up playing gems that most or all in the group have never played before. So without worrying about entertaining an audience, we can take more chances, explore new material as well as get a nice workout on our instruments on some familiar favorites."

Bob Jones is 83. He owns the home with the Blue Room. He has been hosting private jam sessions here for 10 years. "My gig is tuning pianos. I'm a drummer. I didn't want to be a piano tuner. I was a pro drummer."

Bruce Cameron: "One's a real instrument," he says, "and one's not."

Jones takes no offense. He is used to the friendly ribbing. It is the standard drummer gambit.

"My mom wouldn't let me play drums. Too bad," Cameron says, grinning. "That would have saved my career."

For good measure, I deflect with a musician joke of my own:

"What's the difference between a bass player and a mutual fund? A mutual fund matures and earns money."

Bada-bing.

The front room, (aka the Blue Room,) is indeed two shades of blue with beautiful blue granite floor tiles and bright oils of jazz musicians decorating the walls. A framed print of Art Kane's famed black and white photo, Harlem Project, taken in 1958 hangs dead center on the main accent wall.

This is one of those Cali-design tract homes in which the front room ceiling has a steep pitch up to a beam that runs the length of the house. The architecture gives the illusion of additional space, useful in the now-cramped space of the front room.

Jones wants to know if I brought my alto sax. I tell him that I am not even close to the guys here tonight in terms of chops. I tell him that I am in fact not qualified to carry their instrument cases.

"Why don't we set up a different jam with players of a caliber that won't make you feel intimidated?" I tell him the minute that he does, I will be there. Jones hands me a cup of coffee. A familiar face leers from the side of the mug: Rush Limbaugh.

In place of Jones, Art Olson will play piano for the session tonight on a white baby grand that is tucked into a corner of the front room. In the opposite corner, a drum kit. Bill Shreeve plays sax, Bud Shyrock sits in on guitar, and Jeff Blanco shows up on acoustic bass. Hoffman sits behind the kit, and Cameron warms up his cornet and his flugelhorn. Terry Briggs, a former promoter and jazz club owner will sing a couple.

Then someone calls out a song, and they launch. No warm-up. They just pick a chart and go. It's like sitting through a club date, but in a guy's living room.

With the front door open, the neighbors are getting a real treat. I walk outside to see just how far the unadulterated sound carries. 'Tis the season: Christmas lights burn holes in the fog. A long block away, and I can still hear the music.

Otherwise, the neighbors are closed in tonight with the blue light of many televisions tinting the darkness.

At the break Cameron, 68, tells me about an old empty storefront in a part of downtown that is now called is now called the Gaslamp but in the 70s was known as the tenderloin district.

"We had monster jam sessions there. That's where I met Charles McPherson." McPherson is a sax legend who has lived in San Diego since the 1970s. "Just about everybody who was great back in the 70s played there during the day while drunks would sleep on the doorway."

"The repertoire," writes Ricardo Nuno Futre Pinheiro in his 2010 doctoral thesis called The Creative Process in the Context of Jazz Jam Sessions "is usually selected in a conversation between musicians that takes place…prior to performance reflecting a relationship of respect. This might have a positive influence on the improvisational process, namely in terms of producing trust between participants as well as generating creative musical interaction."

"Is the [sheet music] in my bag?" Cameron.

"No. It's in your white book." Shreeve.

All of the players (except Shreeve) read from old fashioned paper charts. Shreeve has an iPad. It simplifies greatly the process of locating music.

"We could have played the song by now." Cameron. He finds it, finally.

"Now you'll really have to play good." Shreeve laughs.

"I know," says Cameron.

The solos tonight, the improvisations, almost all take shape and flow in the same direction: sax first, then trumpet, guitar, piano, bass, drums. There is an unspoken internal guidance system here that governs the rules of the jam. No one polices anyone. The jam is self-correcting. The players know how things should sound. In fact, the only sign that anything resembling rehearsal is going on happens when Shreeve calls for the coda or two to be played over. This is the sort of thing that does not happen in a public jam.

The last song, at around 10:30, is "This I Dig of You."

"Holy shit," says Cameron when they finish.

Shreeve: "This was one of the best mediocre nights we've ever had." He grins.

Later, Bud Shyrock will say this about his own playing, which by all accounts was purely stellar. "I don't know what happened. You have bad nights, mediocre nights, and good nights. And I don't know the factors that make that come to pass."

Then someone tells Cameron he sounded great. "Thanks," he says. "I probably got lucky."