This is one that has been bugging me, so I finally remembered to ask. When you record your voice or any sound for that matter, if you play it back at a higher speed, why does the pitch change? Why wouldn’t the pitch just stay the same and the sounds start/end quicker? Its clearly a higher tone. I found this kind of unusual because I can make sounds faster (for example talking very fast) but the pitch is the same unless I alter it on purpose. Is this just common for sounds when played through electronic equipment?
“Wow! Spider-Man! Are you really friends with the X-men?” "Not since Cyclops tried to use my viewmaster."
(Marvel Team Up #1)
If a 1000 Hz (cycles per second) tone is on a tape that is sped up to twice the recorded speed, twice the number of cycles will occur in the same time. The resulting tone will be at 2000 cycles per second, so the pitch will double.
Don’t concentrate just on the sounds getting closer together. They do, but that’s not all that happens.
Diver’s right. It’s exactly the same as the Doppler effect - you know, when the train is coming down the track the whistle changes from a high pitch to a low one as it passes you, because of the speed of the train.
The same thing happens when you speed up the tape - all the vibrations that you recorded must be played back, so you get a higher pitch.
When you talk fast, you are not performing the same operation. Imagine playing a guitar - you strike the same note 4 times, once per second. now, strike the same note 3 times per second, you are not changing the note you play, just the number of notes you play. If you recorded the first notes and play it back at triple speed (on a traditional tape) you’ll get a higher pitch because it has to compress the entire one second note into one third of a second.
Note that digital recorders are capable of playing back sounds faster than they were recorded without changing the pitch - this is because the player can calculate the correct pitch and reproduce it properly, and then just play it less time - just like playing your voice as if it were a guitar.
Some analog tape players could do it to–they had rotating heads that matched speed with the tape streaming at a higher speed, so the pitch was the same, but the tape was faster. It basically sampled the audio tape.
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In the straight analog scenario, a 200 Hz soundwave becomes a 400 Hz soundwave if its playback speed is doubled, and it can be digitally resampled to match the original frequencies; that has pretty much been covered. I’m just wondering about RM’s reply - not doubting, wondering - are you talking about an analog to digital conversion in the players you mention?
No, what I was describing was supposed to be pure analog. Now, I never saw one, but they were described to me. As an example (only) the tape would stream at twice speed, the tape head(s) would rotate with the tape but slower so that the tape went by the head at normal speed. Thus, it would sample the tape at normal pitch, but the tape would stream at twice the speed.
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