Friday, October 19, 2007

Know your Audio: Van Halen Synth Track Glitch

This was a great submission from a reader:
Hey SomeAudioGuy, Giz has a story up about Van Halen f*cking up their concert. What WAS that...-S.H.

Apparently they decided to pre-record the synth intro to Jump, but on playback the sample rates weren't correct, and it leads to a spectacular train wreck on stage.

Giz has video here (I'd embed here but it's not on Youtube)!

So what happened?

According to the article the the synth was played at 48KHz, instead of 44.1KHz.

But what does that mean AudioGuy?

Well, that's a good question. Ya see Timmy, digital audio is a lot like film.
When you go to a movie what you are actually seeing are individual pictures playing really quickly after each other. To be specific, film travels at 24 frames per second, so every second you're actually seeing 24 pictures. Like a flip book, those pictures become movement as the eye has a hard time adjusting.

Great Guy, but we're talking about sound...


Right, see audio is also stored as slices of information per second, only there are a helluva lot more of them. This is know as the "sample rate". The more samples per second, the more "complete" the sound will be (just like video, the more frames per second the smoother the video). Standard audio CD's have a sample rate of 44.1KHz. Thats 44.1 KILO-Hertz. A "hertz" is a fancy way of saying "cycle per second" (1Hz = 1 cycle per second). A "kilo" of something is a thousand of something, so a KHz is a thousand cycles per second.

That means every second you listen to a cd @ 44.1KHz, you are actually listening to 44,100 slices of sound!

But Van Halen?

Yes yes, so if you record something at one sample rate, but play it back at another, it will change how the music sounds.
Going back to the movie analogy, old movies were shot at 16 frames per second. Well the eye can actually see that flicker between pictures, so over time it evolved to 24 for film (29.97 for DVD, and video games routinely reach 60+ fps). However what happens when you play back an old movie using modern gear?
The modern gear will play back at 24 frames. Thats 8 frames per second, or about 30% faster, than it should. That's why Charlie Chaplin and Buster Keaton movies are so jerky and "sped up".

Movies AGAIN AudioGuy?

Geez, a little patience...
So the intro to Jump was audio at 44.1KHz, but being played at 48KHz. This will speed up the tempo, and by increasing the frequency, will also raise the pitch. As this isn't a huge increase, it wont sound like the chipmunks, but it will frak up all of the instrument tuning. As you can hear Diamond Dave, Eddie, Alex, and Wolfgang couldn't quite adjust to the change, as the synthesizer was now just a smidge sharp (prolly about 10%)...

Oh, well why didn't so just say so?


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