Calculating sound speed for high speed music video

[Christoffer Glans]

I'm gonna shoot a music video with a timebase of 25 fps and shooting fps at 40. How do I calculate the speed up of sound that we will use on location?
Doing 50 fps is easy, it's just double the speed, but 40 or 30 is trickier. How do I calculate this to get the exact percentage in speed?

 

[Chris McKechnie]

Like you said, double-time is easy. For playback on set, you would need to bring the song into an edit platform like FCPX or Premier Pro. Under the speed settings of the audio clip, adjust to the following speed for your various scenarios:

40 fps - 160%
30 fps - 120%

To calculate what percentage, take your FPS (40 in this sample) x 100 then divide by your actual project FPS 25 = 160%

You can then export that clip and write to a CD, your phone, etc and playback at normal speed since it's already sped up. Hope that helps!

 

[Christoffer Glans]

Hmm, I'm using Adobe Audition so the percentage is backwards :001_unsure:
Instead of using 200% for double speed I use 50% in the Stretch and Pitch settings.

 

[Marc Wielage]

You should hire an experienced sound mixer who knows how to do varispeed playback with timecode. I find double-speed to be right on the edge of what regular singers can lip-sync to. On some songs, they can't even go that fast because it's just too much, particularly depending on how much they have to move during the scene.

You're much better off playing the original file in varispeed on the set, rather than trying to use a CD, BTW.

 

[MichaelP]

I blogged about such a process and created a simple spreadsheet to calculate before and after scenarios including pitch correction:
http://24p.com/wordpress/?p=195

 

[M.Halsell]

Thank you Michael

 

[Marc Wielage]

Here's also two very thorough discussion threads on the JWSound group about the challenges of playing back sync-sound on music video sets:

http://jwsoundgroup.net/index.php?/topic/12778-music-playback-questions/

http://jwsoundgroup.net/index.php?/topic/9681-music-video-workflow/

The absolutely best way to do it is to use a laptop with Pro Tools, because you can dial in the actual playback speed to a fraction of a percentage point. The trick is getting timecode back out of the system; not all timecode slates can accept varispeed timecode.

 

[Björn Benckert]

you take the shot speed and devide it with the playback speed.


40/25= 1,60

so speed you music 160%

i would do this: create a normal large 25fps timecode on withe background starting at 00:59:50:00 in a nle.
place the sound track on start even 01:00:00:00 and preferably a few beeps 5 and 3 seconds before music starts.
export the clip. in normal 25fps and good compression.
then import that clip back in the nle and speed 160% put additional info in the frame like"40fps 160%"
export again with ipad codec.

use the ipad for plaback with a cable going from the headphone jack to an amplifyer and also as tc slate infont of camera.
as the tc in the ipad frame is against white you can use a white board marker pen to write additional text on each slate right on the ipad glas