[HN Gopher] Why 23.976 and not 24 FPS?
       ___________________________________________________________________
        
       Why 23.976 and not 24 FPS?
        
       Author : mfiguiere
       Score  : 24 points
       Date   : 2022-10-09 21:23 UTC (1 hours ago)
        
 (HTM) web link (cinematography.com)
 (TXT) w3m dump (cinematography.com)
        
       | lykr0n wrote:
       | The amount of hidden engineering in Analog systems is mind
       | blowing. Imagine how many hours were spent in a lab figuring out
       | the exact right timings, chemical mixtures, and circuit design
       | needed to make modern Cinema exist as we know it.
        
         | nmilo wrote:
         | Sometimes it makes me sad how "boring" digital transmission is.
         | Just pack up your data and send it over IP. Life is too easy.
        
       | petee wrote:
       | Great answer for where 29.97 came from, but I seem to be missing
       | the explanation of 23.976 fps which is suddenly introduced as
       | just an effect of audio post, but not how or why exactly...
       | 
       | Edit: more specifically, if audio was being converted to NTSC for
       | dailies, why would it be 23.976 and not 29.97?
        
         | johntb86 wrote:
         | The traditional frame rate for film is 24fps, which is
         | converted using 3:2 pulldown to 30 fps. 23.976 fps converts
         | using 3:2 pulldown to 29.97 fps (23.976*30/24=29.97).
        
           | Tempest1981 wrote:
           | While reading about 3:2 pulldown, I saw that for PAL (25 fps)
           | there is 2:2:3:2:3 pulldown to 30 fps.
        
             | dylan604 wrote:
             | but rarely does anyone actually do this. normally, a 4%
             | speed change is done to get the frame rate to match. as for
             | the audio, it totally depends on how much effort someone
             | put into it to correct the pitch so that the frequencies
             | are the same in both frame rates. typically, nope. things
             | sound higher pitched in 25fps than they do at the original
             | 24 or 24000/1001 frame rates
        
         | [deleted]
        
         | assttoasstmgr wrote:
         | Because audio for 23.976fps _film_ is playing at the same speed
         | as 29.97fps _video_. Which is really interlaced video at 59.94
         | _fields_ per second. 3:2 pulldown is used to synthesize extra
         | video frames to transfer to NTSC video so for a given instance
         | of time, for every 4 frames of _film_ you get 5 frames of
         | _video_. (23.976 /29.97 = 4/5) The instance of time remains
         | unchanged so the audio is playing back at the same speed. This
         | is all inherited from the CRT days before progressive video
         | playback on flatscreens, and the video fps was tied to the
         | local electrical frequency (50 Hz in Europe vs 60 Hz in USA /
         | Japan) which is how the CRT timings were derived.
         | 
         | Coincidentally PAL video plays back at 25fps, to convert film
         | to PAL they just speed it up from 24 to 25fps, audio and all,
         | which is why if you watch a Euro DVD release of the same film
         | all the actors sound like they just ingested helium before the
         | scene because the audio is playing back ~4% faster.
        
         | cammikebrown wrote:
         | It's the same ratio. 30/29.97 = 24/23.976
        
       ___________________________________________________________________
       (page generated 2022-10-09 23:00 UTC)