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Old September 10th, 2018, 09:19 AM   #1
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Audio recording using external recorder ...

I have a colleague who is recording video at 30fps on a DLSR and is using an external audio recorder. So that the audio doesn't drift, which kHz should he be recording at? Am I right in assuming that an incorrect kHz makes the audio/video drift?

Thanks.
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Old September 10th, 2018, 09:20 AM   #2
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Re: Audio recording using external recorder ...

Any external recorder will drift, you have to correct that in post.
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Old September 10th, 2018, 09:26 AM   #3
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Re: Audio recording using external recorder ...

Thanks. I'll get to him to record sufficient atmos as well ...
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Old September 10th, 2018, 09:57 AM   #4
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Re: Audio recording using external recorder ...

48KHz is the video standard sampling rate for audio. Although some editing systems will automatically accomodate 44.1, it’s best to set all audio recorders to 48. It’s been a long time since I saw a video recorder with options in this, some also offer (offered?) a 32KHz sampling rate - they too should be set to 48KHz.

The next question is usually bit depth / word length.

16-bit is the distribution standard. 16 or 24 are used in shooting. Some softwares bump up to 32-bit internally and for intermediate renders/exports. All of these work, though many prefer to record in 24-bit if available.

So, 16/48 or 24/48 (24-bit / 48KHz).

Drift is speculative - you really don’t know what your systems will do until you try them on longer shots. And, some synchronization methods fix drift automatically (PluralEyes, Premiere sync on audio).

IMPORTANT: for recording with a DSLR (or any camera) and a separate audio recorder, you MUST record at least a crappy track on the DSLR to provide post sync reference. Yes, there are timecode and clapper board methods, but the digital software tools for sync on audio are excellent, and they need audio recorded on both the audio and a/v clips to work.
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Old September 10th, 2018, 01:13 PM   #5
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Re: Audio recording using external recorder ...

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Drift is speculative
Every single recorder I have owned the past years drifted, the zoom h1, h4, the tascam dr5,10,40,60, all of them, sometimes only a few frames on a hour recording, other times a second or more. This can only be corrected in post.
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Old September 10th, 2018, 09:29 PM   #6
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Re: Audio recording using external recorder ...

Quote:
Originally Posted by Stu McAlister View Post
I have a colleague who is recording video at 30fps on a DLSR and is using an external audio recorder. So that the audio doesn't drift, which kHz should he be recording at? Am I right in assuming that an incorrect kHz makes the audio/video drift?

Thanks.
Assuming you're using any at least semi pro recorder (with TC, which are *VERY* cheap now! Such as the Zoom F4 or MixPre3), then it is *NOT* the recorder which is drifting but the camera which is drifting.

As cameras are known to be notoriously bad at keeping accurate time. It is incorrect to assume initially it is the audio recorder's fault if you're using a similar class of recorder.

Your solution here is to use genlock, but that is only a feature offered on high end cameras and expensive timecode boxes. With one exception, the new Ultrasync ONE offers genlock as well as LTC:


The hobo cheap solution: make sure you stop/start your camera every ten (or twenty or so ish) minutes, rather than just letting the interview (or stage show, or wedding, or whatever) roll on and on and on for hours on end with cutting.
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Old September 11th, 2018, 12:37 PM   #7
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Re: Audio recording using external recorder ...

In my experience, cameras keep very good time.
Occasionally an older AVCHD palmcorder may drift by one frame in 90 minutes, but my 4K cameras and DSLR all stay locked for at least 90 minutes.
The Zoom F8, which is the 8 channel version of the F4 will also stay locked with the cameras because it is specifically designed for video use. It can also jam sync timecode with any camera that can output a timecode which saves some time in the edit.
I used to use a Zoom R16 which lost a frame every 10 minutes or so.
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Old September 11th, 2018, 01:04 PM   #8
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Re: Audio recording using external recorder ...

It would be interesting to know if Stu could tell what type of audiorecorder his friend is using.
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Old September 11th, 2018, 10:04 PM   #9
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Re: Audio recording using external recorder ...

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Originally Posted by Tony Neal View Post
In my experience, cameras keep very good time.
Occasionally an older AVCHD palmcorder may drift by one frame in 90 minutes, but my 4K cameras and DSLR all stay locked for at least 90 minutes.
The Zoom F8, which is the 8 channel version of the F4 will also stay locked with the cameras because it is specifically designed for video use. It can also jam sync timecode with any camera that can output a timecode which saves some time in the edit.
Drifting by a frame every hour or so as you say then sounds extremely bad to me. (and we're not even counting time that could be lost when switching batteries, or other things such as jumping back and forth between off and on speed)

So basically you're agreeing with me, "camera's can't hold time".
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Old September 12th, 2018, 01:41 AM   #10
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Re: Audio recording using external recorder ...

I run up to 5 camera's in a 1,5 hour multicam shoot that are not genlocked and none of them drifts, only my audio recorders do.
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Old September 12th, 2018, 03:27 AM   #11
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Re: Audio recording using external recorder ...

Some videographers get concerned about audio drift with external recorders but it really isn't a problem providing you are also recording an audio track on the video for synching. I record weddings and school/theatre productions with 3 or 4 cameras where continuous audio ranges from 30-120 minutes. Sometimes I film 3 productions a week and never have a problem in post.

Sure there may be a slight drift over time, but that is easily corrected automatically in software. Alternatively, if there is no synching software available, the waveforms can be visually aligned very easily. It is also easy enough to align audio by listening for any out of synch by monitoring individual audio tracks with reference to the main track. Even 1 frame audio adjustments in a continuous close up are not noticeable in pauses in the audio.

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Old September 17th, 2018, 12:48 AM   #12
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Re: Audio recording using external recorder ...

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Originally Posted by Noa Put View Post
I run up to 5 camera's in a 1,5 hour multicam shoot that are not genlocked and none of them drifts, only my audio recorders do.
But are you using audio recorders in the same price category as your cameras? Otherwise you're not fairly comparing apples with apples, or even apples vs oranges.
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Old September 17th, 2018, 01:07 AM   #13
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Re: Audio recording using external recorder ...

That's why I was asking Stu if he could tell what type of audio recorder his friend is using.
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Old September 18th, 2018, 02:16 PM   #14
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Re: Audio recording using external recorder ...

Quote:
Originally Posted by Stu McAlister View Post
I have a colleague who is recording video at 30fps on a DLSR and is using an external audio recorder. So that the audio doesn't drift, which kHz should he be recording at? Am I right in assuming that an incorrect kHz makes the audio/video drift?

Thanks.
Actual 30fps or 29.97fps?

Anyway, sample rate and frame rate are different things. What matters is how close the two clocks are. The only way choosing a different sample rate would be the cause of a problem is if it weren't played back in at the same rate, for example recording in 44.1kHz and playing back at 48kHz.

Same deal with fps. If you record at an actual frame rate of 30fps and the playback software treats it as 29.97fps there would likely be a problem syncing audio to it.
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Old September 19th, 2018, 03:31 PM   #15
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Re: Audio recording using external recorder ...

I'm like Roger above - I rarely find syncing things together a big deal at all. Most of my stuff has drummers in it, and their downbeats are always great to use for syncing. Normally, the odd frame here, or there is quite enough - worst case for me would be re-syncing every song or two, if one of the sources is a pain. Stability nowadays is pretty good, but 48 thousand samples a second is never going to be absolutely spot on, and doesn't need to be.
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