Slow Motion sound recording

[Tom Meimer]

Hi,

what would be the easiest way to record sound while shooting variable frame rates? Right now i am just using an small Zoom H1 Recorder on top of the epic to catch some "ambient sound" but as you would expect the audio quality is not great and sycning all up in post is really time consuming. What would be the "best" way to do this with minimized work in post production? It should also work in an one man situation for outdoor filming.

Thanks!

 

[Doug Beatty]

Simple math: 100*[x/project time base] = % speed change
where x is the over cranked frame rate

After syncing to the slate, blade the audio clip at the clap and add the equivalent speed/duration change to the portion after the current time indicator.

 

[Marc Wielage]

What would be the "best" way to do this with minimized work in post production? It should also work in an one man situation for outdoor filming.

I think these two goals are at odds with each other.

Get a separate audio recorder and record at a high sampling rate, like 192kHz/24-bit, along with a very high-quality microphone placed in the best possible position. Once you have that, you can varispeed this material if needed to match the picture playing back at 23.98. (192 = 4 x 48kHz).

Realistically, though, I think hiring a great post mixer and sound effects person to create a specialized sound design for the project makes more sense. Many of the slo-mo scenes shown in feature films have sounds completely created from scratch, using layers and layers of different sound to create the illusion of slo-mo sound to match the picture. The exception might be dialogue, but even then, there are limits to what is possible and practical.

 

[Tom Meimer]

Hi Marc,

thanks for your answer! I guess you are right about the slow motion sound effects, its probably a better idea to hire an post sound guy for this BUT there is also another problem for me:

I shoot a lot of sport stuff and find myself shooting nearly everything in 4K 120fps just to have the possibility to use some shots in Slow Motion although most of the clips get speed up to realtime in the final edit. Bad thing with this method is that i don`t have any sound recorded in camera. Using an simple external recorder and sync up everything in post is the option i am using now but i was hoping for something easier. Maybe some recorder that gets triggered with the REC Button of the epic and records timecode synced files? I guess thats what i am looking for

 

[Michael Romano]

The sound devices PIX240 will act as a monitor, 1080 prores 422 HQ recorder, accept SDI trigger flags to start rolling when you do and has some of the highest cinema application pre-amps and analog to digital conversion available. It also supports TC on SDI etc.

 

[Tom Meimer]

I was already thinking about the PIX240 but i dont really need the Monitor/Recorder function and something smaller would also be nice. Any ideas?

 

[Marc Wielage]

I shoot a lot of sport stuff and find myself shooting nearly everything in 4K 120fps just to have the possibility to use some shots in Slow Motion although most of the clips get speed up to realtime in the final edit. Bad thing with this method is that i don`t have any sound recorded in camera. Using an simple external recorder and sync up everything in post is the option i am using now but i was hoping for something easier.

Nope, that's the way to do it right. And I would suggest recording at 192kHz / 24-bit in order to give you the best possible sound quality in the event of a 2:1 or 4:1 slow-down. I would also suggest you talk to a good re-recording mixer (final sound mixer/editor) to give you some options on how to maximize quality. This is what NFL Films does.

 

[Tom Meimer]

Ok thanks! And is there any way to make the syncing easier, maybe using a soundrecorder that supports timecode and snyc it with the camera?

 

[Marc Wielage]

As far as I know, there is no workable timecode once the camera is running in varispeed. All you can do is clap at the head and sync it by eye. And even that will only stay in sync once the sound is varispeeded back down (assuming you're doing slo-mo).

You could send audio to the camera, but the results won't sound very good, since the effective sampling frequency will be cut by 75%, from 48kHz to 12kHz. This will sound bad.

 

[AndreasOberg]

Marc, isn't the timecode still there even in varispeed but it will only match on the first frame? Or?
/Andreas

 

[Shiblon Wixom]

The sound would match on the first frame only, if you sync by TC; you'd have to process the audio to match the reduced speed factor of the video (x2, x4, etc), then sync in redcine and output a conformed BWF. It should end up with a matching frame count and speed up or ramp with the video file normally. Obviously you don't have pitch controller in FCP7, but many other NLE's do.