Ever catch the TV classics, like the Brady Bunch, on TV Land or such? Any fan of such shows will instantly recognize how the intro song is sped up to save time to squeeze in more commercials). But, how do you physically speed up a song without the voices sounding like chipmunks?
Computer programs to change the speed of recordings without changing the pitch have been around since at least the 1970s.
I assumed they speed it up, then lower the pitch.
I have an audiobook reader app on my phone that will do the same thing, so you can listen to the book in less time.
I read an article about Fresh Air, and it said that they sometimes speed up the voices to make the interview fit into the given time. So this seems pretty standard now.
I thought this was going to be about how sitcoms (and drama shows) don’t even have intros any more. Just credits flashed under the action. Not all, true, but less than before.
But then the question is, how do they lower the pitch without slowing it down?
I don’t know the technical answer to this question, but you can start digging by reading up on [url=“Audio time stretching and pitch scaling - Wikipedia”]audio time-scale/pitch modification."
They speed up Seinfeld reruns on TBS about 9% to fit in more commercials. The entire episode. It’s not enough to notice while you’re watching. Here’s a side-by-side comparison.
If you’ve ever had a CD player go wonky, the answer is obvious. Stretching or squishing digitally-stored sounds doesn’t affect pitch. Just play each sound shorter or longer.
As others have said, the tools to change audio timeline without changing pitch have been around for a while. I use both Sound Forge and Audition for the purpose.
The Mrs is a concert pianist (among other things). I am listening to her trio practice right now. A standard service I provide her (in return for more than adequate pay, I assure you) is to take chamber music movements and produced slowed versions. The audio quality is quite good until you get to around 50% speed (or about 150%, but I rarely speed things up).
A few years back, David Letterman did a silly bit where they ran a rerun show speeded up about 5% - just enough that you could tell, if you were paying attention, and of course being Letterman the slight chipmunking/Keystone Copsing was just part of the fun. Then they squeezed in a new three minutes at the end. All gimmick.
In these days where no trick is too elaborate to squeeze in more marketing, I’d bet that nearly every rerun show that doesn’t have actual edits (remember the syndicated Star Trek episodes that steadily lost scenes over the years?) use time compression. Or may use both, but I suspect the time to edit “unnecessary” seconds is too costly and may now be prevented by syndication and rerun licensing. So add two percent chipmunk, and you’ve got that much more ad time. And only a few people ever even notice.
Blipverts, anyone? 
I use Sound Studio these days; in earlier decades I used SoundEdit 16. Either way, as everyone’s already said, it’s a standard soundwave editor feature. (So is changing the pitch without modifyin the tempo, for that matter).
I noticed years ago when The Simpsons went into syndication…some of those episodes I know/knew really well. Every now and then you’d notice something just seemed “off” somehow. Anyway, they do a pretty common method of cutting both content and “time compression.” The time compression comes that way from the studio, usually, so I imagine it’s done for most other syndicated shows, too. More than you wanted to know about the cuts and compression on every Simpsons episode, maybe, here: http://www.simpsonsarchive.com/episodes/scg-faq.html#whycut (the Syndication Cuts Guide is a mixture of fascinating, “I don’t have time for this sh**”, and depressing).
In addition, free programs like Audacity include all the usual time-scaling and pitch modification filters if anybody wants to play around with it. There is audible artifacting that occurs if you try to time-scale or pitch-shift too much, but within a reasonable range, it sounds okay.
Several decades ago, when I was doing audio, our tools for shortening things were limited to a) speeding things up and b) literally cutting out spaces between syllables, breaths and other pauses.
Trial and error taught us we could easily speed things up by about 3% with nearly no one able to detect it. Deleting pauses (much easier to do with today’s software) makes for an odd rhythm, but doesn’t change pitch in the slightest. I’ve noticed it seems to be used a lot on legal disclaimers at the end of commercials.
Anyone ever notice this: I used to be watching jeopardy and I noticed that every couple seconds a frame was missing and it jumped. As soon as I noticed this once I couldn’t help but see it all the time and it ruined it for me. Obviously they were fitting more ads in, but I don’t think they do it anymore.
I understand that back in the 30s/40s at the Termite Terrace, they did alter Mel Blanc’s voice over for Daffy Duck.
This is not true. If you stretch, you do have to create more sound, and if you squish, you have to remove sound. To do it well, and not the really choppy sounding effect you get on the CD player you mention, actually takes some processing power.
Also, to the OP: it’s not just the intro that is sped up. The entire show can be sped up to fit in more commercials. Though you can’t go overboard, or it will break the timing. That’s when they go on and actually cut out content, cutting away faster or cutting out scenes.