Does sound have a ‘frames per second’ like video? If not, how is it slowed down and sped up?

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Does sound have a ‘frames per second’ like video? If not, how is it slowed down and sped up?

In: Physics

3 Answers

Anonymous 0 Comments

Sound recordings does have samples per second. It is possible to play back the sound at different samples per second in order to speed it up or slow it down. However unlike pictures our perception of sound is based around frequency which is based on time. While video framerates are usually in the tens of frames a second sound is usually sampled at 48 thousand samples per second. This is because the frequency information that you perceive is encoded in the samples. In order to capture a sound you need twice the sample rate of its frequency. So while it is easy to speed up or slow down video playback without altering the pictures you perceive if you do the same with the sound playback you will change the pitch of the sound. It is possible to change the playback speed of sound without changing the pitch but this requires fairly complex math to do.

Anonymous 0 Comments

* Yes.
* Digital audio does have something almost exactly the same as frames called “samples”.
* A sample is simply the value of the voltage on the wire at a given point in time.
* Using these samples, the audio system can re-create the voltage wave that can be fed into an audio amplifier just like the signal from a mic.
* So when digital audio is recorded and played back, it has to be done at the proper “sample rate” which is the same as a video’s “frame rate”.
* Said another way, it has to use the proper “samples per second”.
* It’s a little different with straight up analog audio because it’s based on the medium upon which it’s recorded.
* Mostly analog audio is recorded on magnetic tape.
* In order for it to sound correct, the tape needs to be played back at the same speed as it was recorded.
* So in that case it would be a unit of length passing by the playback head over a given amount of time.
* So something like “millimeters per second”.

Anonymous 0 Comments

To add to what others are saying, there is a technique called wavelet transforms that can allow sound to be sped up without changing pitch. It is kind of like listening to music, and writing down the notes that are played as sheet music. If you know that you play C-E-G-C, you can play them fast or slow, and still get the same pitches. In fact, that is literally how .MIDI files work. .mp3 files do something similar (with a lot more notes than could be written down on sheet music).