Recording external audio source

[Andrew Plumb]

If you're recording live band performances then I'd say definitely go the H4 route. You'll be able to use the H4 to record off the house mix and use the HV20 audio to sync video to and to get more ambient sound in the mix.

Others will have more experience than me (it's my expensive hobby ;-) w.r.t. synchronizing external audio with video, but my guess would be that it's more of an issue with spoken dialogue than musical performances. Music is (mostly) one long audio take (the audio is your timeline) with a selection of camera feeds to choose from, whereas dialogue tends to get cut'n'pasted a lot to tighten things up.

[Jay Cowley]

Originally Posted by Andrew Plumb

Jay, 15m is pretty long for an unbalanced cable - that's one long antenna! You're probably picking up all kinds of 60Hz and other electrical noise along the length. If you're committed to using that mic (is this the one?) for recording audio, definitely try a shorter cable. If shorter isn't an option, wireless may be the only way to keep the mic-to-transmitter and receiver-to-camera connections short.

That said, you might be able to pick up something like a Zoom H4 for the same price as a wireless mic kit. Then you can put the Rode back on your camera to capture reference/background audio and capture higher-res audio at the source with the H4. You then have the option to use TRS/XLR balanced connections to better quality mics and sources, recording at higher bit-rates on the H4.

So many ways to spend more money. ;-)

I don't know if I could return my rode-video mic, it's been more than 14 days from the store I bought it from. I was just looking for a simple external mic that i can use to record dialogue with, since I can't use the mic on my camera or put any mic on my camera since it picks up the motor noise of my 35mm adaptor, i figured the rode videomic would work fine as a cheap mic to go on a boompole

It does work properly when the camera is unplugged and running of battery, so if i need to, i guess i can use the extention cable and then run camera of battery. but this certainly will become inconvenient at times, thats why i thought there might be a way to ground the camera or power adaptor somehow to get rid of this noise.

[Andrew Plumb]

Originally Posted by Jay Cowley

I don't know if I could return my rode-video mic, it's been more than 14 days from the store I bought it from. I was just looking for a simple external mic that i can use to record dialogue with, since I can't use the mic on my camera or put any mic on my camera since it picks up the motor noise of my 35mm adaptor, i figured the rode videomic would work fine as a cheap mic to go on a boompole

It does work properly when the camera is unplugged and running of battery, so if i need to, i guess i can use the extention cable and then run camera of battery. but this certainly will become inconvenient at times, thats why i thought there might be a way to ground the camera or power adaptor somehow to get rid of this noise.

Ah, I missed the bit about the noise going away when the camera was unplugged from the wall. The core issue probably still is the 15m unbalanced cable acting as an antenna.

Re. the 35mm motor noise you're trying to get away from. If it's high enough in pitch you might be able to get away with mounting the Rode on a hotshoe extender and making an acoustic shield out of some heavy (weave) fabric to put between the mic and the camera.

Simple experiment: Wrap an old shirt (thick material and/or multiple wraps) around a coat-hanger and see what effect sliding it between the 35mm and the mic has. If that doesn't work too well, try putting a piece of cardboard in the coat-hanger and wrap the shirt around that. You don't want air to be able to "blow" through, but it needs to be floppy enough that it won't vibrate like a drum skin.

The stiff cardboard should help deflect the motor sound away, but you probably don't want to use cardboard in the final solution because you'll reflect other sounds into the mic from other angles. Pick a non-porous but floppy material to soak up the high-freq sound. ...It's sort of like building a pop shield, but for a different purpose.

[Peter J Alessandria]

Originally Posted by Joseph H. Moore

John,
While the audio can creep over a long period of time, if you're introducing regular cuts in your edit, that should allow you plenty of opportunities to keep in sync. Now, if you're trying to keep an hour long straight through cut in sync, yeah, that might be a challenge.

From one of the B&H reviewers:

"With my camcorder the audio needs to be stretched by 100.049% to stay in sync. This is a very simple solution with the right software, but it caused some frustration until I worked out the ratio which seems to be very consistent with all of the recordings I have made so far."

[Andrew Plumb]

Makes sense. Bare in mind that if you record across a broad range of temperatures outdoors (summer versus winter) you'll probably see absolute and relative drift in those timing numbers. Simple semiconductor physics. ;-)

Roughly translated, unless all your equipment happens to be synchronized to a single time-base, you'll need to calculate and apply the ratios yourself (unless your NLE can do it for you):

1. Find a start reference peak/clap at the start of your audio in the camera footage: T(AV.start)

2. Find an end reference peak/clap close to the end (it's the cumulative timing error you're most worried about) of your audio in the camera footage: T(AV.end)

3. Find the same start reference peak/clap at the start of your externally recorded audio: T(audio.start)

4. Find the same end reference peak/clap at the end of your externally recorded audio: T(audio.end)

5. Pick a reference time-base; externally recorded audio for a more music-oriented performance.

6. Calculate the ratio to multiply the AV track by:

= (T(audio.end)-T(audio.start))/(T(AV.end)-T(AV.start))

7. Repeat for all camera sources, be they HV20, cellphone, etc.


Sanity check:

- if the AV finishes sooner than the audio, you need to multiply by a ratio greater than 1.0 to stretch the AV track. Numerator should be greater than the denominator.

- if the AV finishes after the audio, you need to multiply by a ratio smaller than 1.0 to compress the AV track. Numerator should be smaller than the denominator.

[Andrew Plumb]

Well, whether it's a lucky coincidence or a direct result of these sorts of discussions, the latest e-mailed B&H newsletter links to a couple of relevant items on their website:

- Guide to Alternative Microphones for use on a Boompole

- Guide to Understanding B&H ENG kits