Recording external audio source
 

Hi,

I connected a Roland keyboard to the HV20 using mini-phone plug (from RCA outs). I get a low hum immediately so I had to turn on MIC ATT. However I notice a gate effect after that meaning I hear the volume being capped frequently.
I tried changing the volume but same effect (and low quality). Any idea if this is normal?I'm sure the audio signal is fine since when I hook it up to PC speakers it sounds just perfect.

Strange that I need to turn MIC ATT in the first place.

Thanks
Luc

Luc - I'm not a musician nor am I familiar with that keyboard. But check if there is a line/mic switch on the keyboard output and set it to "mic". A "line" setting is a hotter signal which may cause what you are experiencing. Alternatively, get a cheap mixer (Bheringer makes some nice ones). That will allow you to set your levels, mix multiple sources and output a nice signal to your camera.

In addition to the line versus mic issue, you could be creating a ground-loop if your camera is plugged into the power adapter.

Try running the camera using battery-only to see if the hum goes away.

That was it! Using the battery it works just fine now, never have thought that could be the problem.

Since it looks like it might be a ground-loop problem, some other things to try:

- If they aren't already, plug the Roland and Canon power cables into the same outlet/power-bar. This will cut down the likelihood that they're connected the long way through the power infrastructure.

- If that doesn't help, try flipping one of the power plugs around - might be difficult if your power cables are keyed (one prong's wider than the other) and/or the Roland has three prongs. It's not uncommon for cheap power-bars to have flipped phases between sockets.

- If none of the above works, but the Roland does have TRS or XLR balanced outputs, you could drop by your local pro-audio/music store and pick up a proper pair of cables to connect the balanced outputs to the HV20's unbalanced mic inputs.

I had this same issue, but with a rode-video mic. The video mic uses a battery, but when I had it plugged in through a 15m extention cable to the camera, i heard a buzz sound. If I unplugged the power cable from the camera went away.

If i removed the 15m extention cable, it removed the buzz completely, regardless whether the camera was plugged in or not.

The problem here though is that I will need to have the camera plugged in and still use a the rode videomic on a boom pole. What will I do here?

Not an expert but maybe with 15m length you need a different gauge cable?Although you would think it doesn't take that much power to need different gauge so no idea.

In my case I had both the Roland and Canon plugged in the same outlet. I do have an extended battery which lasts many hours so no problem.

By the way the HV20 video is on http://www.youtube.com/watch?v=ZE6qm4aCaaY (actually that's the one that has some gate issues but on youtube you lose anyway most of the quality so you won't notice much).

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'm not an audio expert nor am I familiar with the Rode Mic but if you could connect the mic via an xlr balanced cable & get you a Beachtek or XLR Pro adaptor at the camera end, I would think you would eleminate the hum. If not, pick up a decent XLR mic for the boom.

The gottcha is that both the Rode mic and HV20 are unbalanced stereo I/O. The XLR ground-lifting trick won't work because neither side can source or sink a differential balanced signal.

Switching to a different mic would at least let you pick something that works.

The deal with a Beachtek type solution though, allows a long balanced cable from the mic to the Beachtek input and only a 6 to 12 inch cable from the Beachtek output to the unbalanced mic in on the camera. Or am I wrong and the Beachtek XLR inputs or not balanced. I know I've been running a dynamic Seinheiser mic with over 50' of XLR cable to my XLR-Pro adapter without picking up any hum or induced noise. I guess I need to check the specs on the XLR-Pro and the Beachtek. I know I wouldn't ever separate my camera from my XLR-Pro adaptor. It has been a real blessing for improving audio capture to the camera.

It may be worth noting that the XLR Pro has two different grounding settings while the beachtek only has one. That might be relevant.

I was thinking about trying the

Rode Video Mic ->
rodeo mini to XLR Adapter ->
XLR cable ->
XLR to mini converter box ->
camera

chain with my GL2 some time.

Bummer if that doesn't provide any more protection from interference than just using unbalanced mini audio cable.

Shayne Weyker
http://weykervideo.com

Ah, good. Since the Beachtek converts to a balanced/differential signal for the long-haul it should be ok... And looking at BHPhoto, a Zoom H4 does cost less than many of the Beachtek options.

If I were making the decision, I'd opt for the H4 field-recorder approach because you're only going to get 12/16-bit lossy-compressed audio out of an HV20 recording to HDV.

I'd like to try an H4 type solution for capturing sound but I was told it's dang near impossible to keep an external audio stream in sync with the video. Lots of my videos or of live band performances that run up to an hour. Have you had any personal experience syncing an external audio source with video in your RLE.

I know what you mean about the sound. I don't know whether it's my Pinnacle doing it but when I capture my video it separates the audio from the video. I haven't figured what it's doing but the capture folder winds up with two identical size wav files. I think the audio sounds better when I play the wav files than it does after I've outputed to a DVD format. Incidentally in the output selection the audio is designated as mpeg1. Does that make sense. It offers to do Dolby Stereo which I haven't tried because I'm not sure if that will limit the client to need dolby in order to hear the audio.

Audio is just about as important to me as the video so I need to keep working at improving my audio. I think they really screwed up by limiting the audio quality in the HDV specification in order to still fit an hour of HDV on a minidv tape. I wonder if a direct to disk solution would improve the audio even though I'm still going to render to DVD and not HD DVD for the time being? If it does, it certainly would be an expensive and time consuming way of improving audio capture. I guess I'll get me an H4 and get my hands dirty in post op to see. I was ok with the audio capture in standard DV even though it probably wouldn't live up to H4 audio.

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.

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.

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.

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."

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.

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