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Activity Forums DSLR Video Does audio has a rate like frame rate?

  • Does audio has a rate like frame rate?

    Posted by Nitai Lev-oren on August 26, 2016 at 12:25 pm

    I’m asking this because I’ve heard if you shoot 30 fps or 23 fps you will have a problem with the audio
    Let’s say you record on double system on a DSLR and you have an external recorder. the audio will have a lag, is this true?

    Jim Framer replied 2 years, 1 month ago 4 Members · 10 Replies
  • 10 Replies
  • Blaise Douros

    August 26, 2016 at 5:50 pm

    Audio has a sample rate, measured in kilohertz. Standard audio for video is recorded at 48 khz. This does not change with framerate; audio will always be the same, whether you’re shooting 23.976 fps or 59.94 fps.

    Unsynchronized devices will “drift” out of audio and video sync due to tiny differences in their electronics. For this reason, timecode/genlock hardware, usually found on professional cameras, can be used to synchronize the clocks of each device, and ensure their recordings are synced.

    In practice, unless you have hours and hours of continuous video, you won’t get noticeable drift these days. I’ve never had a problem with noticeable drift in a modern camera and external audio recorder.

    Perhaps you can tell us what you’re trying to accomplish, and we can give you more than very general answers?

  • Nitai Lev-oren

    August 27, 2016 at 2:30 pm

    so the audio speed is constant?
    but if you shoot at 60fps it’s another speed of the video so how it can be like that?

  • Mike Smith

    August 29, 2016 at 9:49 am

    I’m not entirely clear what it is that you are trying to achieve here.

    As I think Blaise tried to explain, the audio sampling frequency for your audio is normally unaffected by video frame rate considerations.

    Your editing software will try to play video at the rate indicated in the video file or the rate you ask it to. It will try to play the audio using the sampling frequency indicated in the audio file – or at another speed if you ask it to. If you try to synchronise audio with video from dslrs this will probably work very well, unless you are going for very long takes where you might (or might not), as Blaise indicated, see a gradual “drift” out of sync over a long period. This is not likely to be much of a problem in most editing situations.

    If you are having trouble with this then the background here might help:

  • Blaise Douros

    August 29, 2016 at 7:13 pm

    Because more frames per second just means that you’re slicing one second of time into 60 pieces instead of 24. A second of audio is a second of audio, regardless of how many frames per second are captured in the video.

    Now, if you shoot 60 fps and do a framerate convert to 24, then the audio slows down to match the video. But if you play 60 fps back in realtime, and you play 24 fps back in realtime…there’s no change in the audio.

  • Nitai Lev-oren

    August 29, 2016 at 7:20 pm

    ok, but how many video frames can fit into 1 second of video?

  • Blaise Douros

    August 29, 2016 at 8:26 pm

    …it depends on the framerate. That’s literally what framerate means. Frames Per Second. FPS. The number of frames in a second.

    24 FPS: 24 frames in a second. 60 FPS: 60 frames in a second. If you shoot a Phantom high speed camera, you can shoot 1000 FPS: 1000 frames in a second.

    If you play back a 1000 FPS clip at realtime in 1000 FPS, it will be one second of video–and if you recorded audio in sync with that, it would play back at realtime, as well. Now, you can slow the video waaaaaaaayyyyy down, and still get smooth motion, because there are more frames there that your eye can perceive–the audio would then slow down by an identical amount. Play it back at 500 FPS? Audio slows down to 1/2 speed. 250 FPS? 1/4 speed.

    I suspect that you are confused because you believe that there is only one “correct” framerate, and that all video plays back at that framerate regardless of what framerate it was shot. This is not the case.

  • Nitai Lev-oren

    August 29, 2016 at 9:06 pm

    thank you for the answer.
    how many frames our eyes can see (online on real life I mean, I think it’s more then 60fps)?

  • Blaise Douros

    August 30, 2016 at 12:06 am

    60 is about the max. Even that is debatable; that’s why we shoot with a 180 degree shutter, to minimize flicker at lower framerates by introducing a certain amount of motion blur to help connect each image.

  • Nitai Lev-oren

    August 30, 2016 at 6:17 am

    thank you

  • Jim Framer

    April 14, 2022 at 1:01 pm

    I feel like no one adequately explained this. Now, video is measured in frames per second, but audio is not; audio is measure in sampling rate. For the purposes of answering your question however, I’ll call the audio sample rate frames per second (or FPS for short).

    A typical video is played back at a speed like 24 FPS or 60 FPS. Audio is usually played back at about 48,000 FPS. Yes 48 THOUSAND times per SECOND.

    So, how then is this possible? Simple: video playback and audio playback happen *independently* of each other. Video and audio are in no way related except for the fact that they’re kept in sync by timing mechanisms. Put differently, audio and video are not played back by the same thing. They are played back by completely unrelated mechanisms; our brains are simply fooled into thinking they’re related like they are in real life. That video game you’re playing renders graphics at 30 FPS, but audio at 48,000 FPS. This is what we mean by 48kHz sample rates.

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