The Robbery - S1-E2
Continuity mistake: Jerry is being grumpy on The Couch with his friends for giving up The Apartment, arms crossed. Notice his right sleeve, down till the wrist. When Carol enters the room with her husband for the first time, Jerry is still with his arms crossed but the sleeve is up, mid-length. (00:20:35)
The Robbery - S1-E2
Continuity mistake: Jerry is back from Minneapolis, and he puts The Keys down on the kitchen isle. When Elaine walks in with the plunger, The Keys have moved forward and more towards the center. (00:04:45)
The Robbery - S1-E2
Continuity mistake: During the initial conversation when the camera is on Elaine there's a chair prominently featured in the background, with a jacket on the back. The chair turns around between shots - in particular, when Jerry proudly proclaims himself "Master Packer" it is positioned at the desk instead of facing towards the camera. (00:01:10)
The Robbery - S1-E2
Continuity mistake: George is chatting with Elaine as he is waiting for Jerry. Elaine splits an Oreo cookie. When he mentions her "price range", she is not seen fully but her left hand is in frame and she brings it up. When George turns around to address Jerry though, it's her right hand to be raised. (00:03:20)
The Robbery - S1-E2
Continuity mistake: George sits down at the diners' table with Jerry after his bathroom (and mirror) break. When Jerry asks him "So what are you getting?" he is holding the menu in a different way between front view and reverse. (00:18:40)
The Robbery - S1-E2
Continuity mistake: Jerry has just won the contested deed for The Apartment beating George. Look at The Jacket on the counter. When Kramer makes his trademark entrance, The Jacket is placed differently. (00:16:40)
The Robbery - S1-E2
Continuity mistake: When Jerry tells Elaine to "Do it in the shower", he gestures with his fancy retractable umbrella. But he is holding it by opposite ends in the two consecutive shots. (00:02:30)
Answer: Composer Jonathan Wolff used a synthesizer, although in seasons 7-9, a real bass is used in addition. Wolff also recorded himself making hundreds of mouth noises, pops, and slaps to add to the synthesized bass licks so that each episode has a different theme. The only real "back-story" is Jerry Seinfeld was having trouble coming up with a theme song and talked to a friend who happened to know Wolff. They wanted to avoid that cheesy late 80's sit-com theme song and Wolff came up with what we enjoy now. Jonathan Wolff has also talked about this further in interviews, recently Reed Dunela interviewed him, so for a fuller account of his story; check out "The Wolff of 116th street".
Bishop73