Audio Inputs

J

jdogg0075

Im sorry if this is a dull noob question. Ive done some research and i still don't get some of the ideas of audio inputs. I get how XLR has phantom power and this is the best and that 1/8" mini jack is crappy because its unbalanced. My question is i keep seeing this 1/4" jack input for stereo.

Im just really confused on what inputs are balanced and what ones are not? If you could give any help.

-Thanks in advance
 
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Since balanced audio requires 3 conductors, it's a good rule of thumb that all professional quality sound gear will have XLR connections, which have a signal+, signal-, ground and shield (3 conductors) to carry balanced audio.

If you buy a camera with a 1/8" stereo miniplug as input, the trick to getting noise free audio is to use an XLR pre-amp mixer (like the Beachtek) which outputs an unbalanced, stereo signal suitable for your 1/8" input jack. Then keep the wire between the balanced pre-amp and the camera as short as possible (up to 3 feet is probably safe in most environments), to reduce noise pickup.

Doug

p.s. Balanced audio gear provides for excellent noise canceling, so you won't get that background hum from your wires, which act like radio antennas. The more electrical equipment you have around you, the more important this becomes.
 
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oakstreetphotovideo said:
p.s. Balanced audio gear provides for excellent noise canceling, so you won't get that background hum from your wires, which act like radio antennas. The more electrical equipment you have around you, the more important this becomes.
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Oh so true, I was filming an interview a few weeks ago and unknowingly picked up some minor background interference from the guy's cell phone. Didn't ruin the shot, but its not 100% what it could have been.
 
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All balanced and unbalanced means is its stereo or mono. Balanced means it has both a right and left channel (stereo) and unbalanced means it has a single channel (mono). Now most shotgun microphones (including shotgun mics for movie dialogue) are indeed mono and unbalanced, the only reason why you DO want a BALANCED input is because a balanced signal can travel much farther without much resistance.
It all gets pretty complicated from here, but what you need to know is that an unbalanced signal will start to give you some buzzing if the cord is more than 15-20 feet.
With a balanced XLR input, you have nearly unlimited length because a balanced signal can travel much farther without much resistance (buzzing).

Another big reason why you'd want an XLR input OR an external device WITH an XLR, is because typically the preamps you'll find in an XLR input are far superior to that of a 1/4 or 1/8 inch jack.
1/8 inch and 1/4 inch will be fine so long as you can get an external preamp like beachtek. I actually use a battery operated 10 channel studio mixer for my audio. The preamps are even better and its only 100 bucks (behringer eurorack ubb1002).

Hope that helps.
 
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OrchidsofWrath said:
All balanced and unbalanced means is its stereo or mono. Balanced means it has both a right and left channel (stereo) and unbalanced means it has a single channel (mono).
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This is absolutely, 100% wrong. The rest of your post is dubious. A balanced signal is not stereo. It has two wires carrying exactly the same signal with one of them inverted. I'd go into details about how this is used to cancel noise, but that isn't important. What is important is that a balanced audio signal provides a way for the pre-amp to cancel the noise. Using only 2 wires (signal and ground), you must rely on the shielding in the cable to protect you from noise, and that is generally inadequate around a lot of electrical equipment.

If none of that made sense, then all you must remember is that balanced equipment offers a means for noise cancellation that is not available with unbalanced equipment. It has nothing to do with being stereo or mono. Finally, if you want a minimal noise floor (very clean audio), you want to use balanced gear.

Doug
 
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Hey thanks everyone for posting. Im really starting to know more about audio now. It really has helped. The only thing im struggling with now is finding the right recording device. I wanna look for one that can record in 24 bit that would be nice. But basically my set up would be a shotgun mic on a boom pole run with xlr cable to a beachtek i think its called pre amp then to a mini jack to the recorder.

Im not sure if i want to use mini disk player to record because of the analog to digital conversion and i really cant find a cheap DAT recorder. Im still looking for advice on a recording device. Preferably 24 bit and all digital. Probably to much to ask for on a budget. Any thoughts?
 
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Unless there are incredibly good reasons not to, with digital production, it's almost always better to have your audio go into the camera.

Firstly because it means everything is in sync. Secondly, because despite the non-professional inputs, the actual digital audio set of even incredibly cheap camcorders has always been excellent. In fact, I've known of a few film makers shooting on film who recorded their audio onto DV using cheap camcorders. A camcorder is really a DAT machine that also records images.

There are however exceptions:

If you've a minijack input and you intend running around a lot with the camera, the interface isn't robust enough and you may get an erratic signal.

If you're shooting on either a VX2000, VX9000 or an early PD150 the preamp is a disaster area and will generate unacceptable noise levels.

Other than that my advice is to put the audio into the camera.

Next - if you decide to record it to an external device the mini-disc is fine. The problem with mini-disc is it a very strong compressed audio medium and isn't ideal... and you may also find that a shotgun mic needs a preamp between it and your recording device.

In terms of other devices there are a lot of very good hard disc recorders out there Marrantz make good ones.

However, by the time you've bought your Beachtek XLR to mini-jack adapter, a preamp and a hard disc recorder... you could have afforded to buy a camera that has XLR inputs.
 
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However, by the time you've bought your Beachtek XLR to mini-jack adapter, a preamp and a hard disc recorder... you could have afforded to buy a camera that has XLR inputs.
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Clarification: If you purchase the Beachtek adaptor (or a similar device), you can record directly on a camera with a mini-jack from XLR microphones.

As Clive points out, recording directly to the camera has several advantages. I also agree with Clive that buying a camera with XLR inputs is often the best solution. I will not purchase a camera without XLR inputs, but I understand that some people already own cameras without them, or may wish to purchase a less expensive camera. As Directorik pointed out here or in another thread, it is worth investing in good audio gear (XLR microphones, etc.) because your audio gear will be with you forever if you care for it. By using an XLR adapter, you can invest in good, quality microphones.
 
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Clarification of the clarification:

When I mentioned the Beachtek, Pre-amp, recorder combo I was trying to point out that camcorders have pre-amps so they don't need one... but most recorders don't, so a straight mic through Beachtek to recorder only works if the Beachtek is the model with a pre-amp (most don't have one).

Of course if the recorder has XLR in, then you don't need the Beachtek... but for a mini-disc with an mini-jack in you still do.

Should have made myself more clear.
 
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I was thinking of making a line balancer that uses regular 1/8" stereo plugs. It would have a mono 1/8" input, then provided a balanced run through WAY cheaper stereo headphone extension cables, finally outputting to mono again at the other end. That would minimize the RFyness of mics like the ATR55 on sets with lots of cables (I suffered from this alot before going balanced at bigger expense).
 
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Ive pretty much decided on just saving up as much money as i can to get the DVX 100A. My budget for that camera will be $2770 for hard drive, tripod, mic, ect. Vs. my budget im willing to spend on the HV20 Which is 1500 including same accessories and larger Hard drive for HD video.

In the long run i think the xlr inputs will make a difference on a ton of things plus ill be using a much better camera. If the camera is just as good at recording audio then doing it separately im going with xlr inputs. Thanks for all the audio help.
 
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Balanced audio can also use what most people would consider a stereo headphone jack. (an 1/8 inch, or 1/4 inch with three contacts), as knightly touched on in his post...

jdogg: the DVX is a great camera, I've used it several times and can definitely understand your desire to get one. As a current owner of an HV20 I thought I'd throw out a couple thoughts.

the HV 20 doesn't "technically" record HD video, it records HDV video, which is compressed using mpeg 2 compression, and it ends up being the same size on disk as standard definition DV. an HV20 in conjunction with a beachtek gives you the same audio inputs as the dvx, and it sounds great.

It's a minor annoyance, but something I recall from using the dvx is that if you're shooting in 24p (and possibly 60i, never used it that way so I can't say for certain) is that there is an echo in the headphones, so monitoring your audio is a bit of a pain. The reason for this, as far as I understand it is that you hear both the live audio and the audio synced with the 3:2 pulldown encapsulated video. It's a bit of a shock the first time you hear it because even in a dead room it sounds like you're in an echoey hallway. With the HV20 and my beachtek I don't have that issue.

On the other hand, the HV20 doesn't put the proper flags on the video to make 3:2 pulldown removal automatic, so there are several steps you have to go through to work with the progressive frames in post whereas with the dvx it "just works". Of course if you wanted to step up to the HV20's big brother, the XHA1, I don't believe that is a problem, and it offers you all the same easy control over manual functions as the dvx while still capturing a much higher resolution image.

Here's a quick rough cut from the current short I've been working on. This hasn't had any additional work done to it other than assembling the raw footage. Nothing was done with the audio or the video other than that. I didn't do the pulldown removal, so the image is a little choppy compared to how it would be working with proper progressive frames... http://vimeo.com/385036

I believe it was a sennheiser shotgun mic running into my beachtek, but it may have been a different make, I don't recall as this was actually shot back in November. Also I suppose I should mention I've never considered myself to be a shooter really.. I signed on to this project to do the effects work, and was roped into DPing as well.
 
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knightly said:
I was thinking of making a line balancer that uses regular 1/8" stereo plugs. It would have a mono 1/8" input, then provided a balanced run through WAY cheaper stereo headphone extension cables, finally outputting to mono again at the other end. That would minimize the RFyness of mics like the ATR55 on sets with lots of cables (I suffered from this alot before going balanced at bigger expense).
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I've done the converter from balanced to unbalanced, with about a 100x gain, but I'm not sure the unbalanced to balanced conversion would be as trivial. Essentially, you just invert the signal and send the inverted and non-inverted signals down the two signal wires, but the two signals must be perfectly matched in phase and amplitude. I'd have to build something to see how difficult it would be. I'd recommend using 2 high quality operational amplifiers (a matched set, or a dual amp). Use the inverting input on one and the non-inverting input on the other. I'd also use a little gain to provide a stronger signal on the long wire.

If you want to do it with passive components, it could get expensive, because you'd probably need a high quality, audio transformer.

p.s. I had good luck with the LM833N operational amplifier. It is very clean and the spec sheet for it has a schematic for a simple balanced amplifier circuit.

Doug
 
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