How to record slow-motion sound

By HaLo2FrEeEk
Nov 11, 2009
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  1. I've seen high-speed videos shot with multi-thousand fps cameras, and the ones that have sound have slow motion sound. I want to know how to film this slow motion sound. For a good example of exactly what I mean, watch mythbusters, they do slow motion footage with sound all the time.

    I've tried just recording a regular sound and stretching it in a program like Vegas, but then it gets all distorted and...idk how to explain how it gets, here's an example:

    Normal:
    http://infectionist.com/misc/odst_egg-hitchhikers.mp3

    Stretched (x2):
    http://infectionist.com/misc/odst_egg-hitchhikers_stretch.mp3

    Notice the echo? That happens, and that's only when I stretch it to x2, high-speed cameras film at many many times normal NTSC framerates. Does anyone know a way I can record at higher...framerates? I'm not sure if that's what you would call it when referring to audio, but you should know what I mean.
  2. HaLo2FrEeEk

    HaLo2FrEeEk TechSpot Enthusiast Topic Starter Posts: 225

    Anyone? Bump.
  3. fw2004

    fw2004 TechSpot Enthusiast Posts: 203

    Let me think about this.
    I'll try working with my audio app for a while.

    I think your problem is the sampling rate.
    If you are going to play back at a faster rate than you recorded at, you lose definition.

    I use Cool Edit 2000 for 10 years. Let me see what I can find out with that app, which would apply to any audio editing app.

    Cool will record at rates from 6KHz to 192Khz. As you are probably familiar with MP3 files, the higher the sample or bit rate, the higher the quality (and the larger the file).

    If you want to play back at a faster rate, you need to bump up your recording rate as well, so that you get better definition.
    If you are currently recording at 20Khz, try 40Khz.
    Of course, the faster you record, the less stretching you can do.
    If the app you are using to record will handle rates of at least 192Khz, I think you will get some good results for stretching up to 4X.
    If you want more than that, you will probably have to record a lot faster than 40Khz, and play back a lot faster than 200Khz.
    For this, you will need a professional sound card.

    Hope this helps

    FW
  4. HaLo2FrEeEk

    HaLo2FrEeEk TechSpot Enthusiast Topic Starter Posts: 225

    I'm using Sony Vegas to record audio. It records uncompressed WAV files at 44,100 Hz (so I guess 44Khz?) at a variable bitrate, but the source file for the one I linked to in the first post is 1411 Kbps. So your answer is that I should record at a higher sample rate, not a higher bitrate? I'll check it out in Vegas and see what I can do. Thanks!
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