HVX Audio Question - mixer bypasses camera pre-amps?

[John Froton]

Barry,

Is it true that you can bypass the preamps in the HVX by switching to line level on the XLR inputs?

It does not seem that this would be so because isn't it the preamps that allow you to raise and lower the signal level with the dials on the camcorder? This can still be done with a line level signal.

My reason for asking is that I am using a mixpre mic preamp and recall reading posts where people say the preamps in a mixpre are better than the preamps in the HVX --- so it leads me to think that the preamps in the mixpre can somehow take over/replace/or bypass the HVX preamps.

Can you enlighten me on how this works? I have posted in the audio forum with more specific questions regarding settings and levels but thought that this forum would be appropriate to ask a more general and more HVX specific type of question.

Perhaps my understanding of what a preamp is or does is not accurate.

Thanks for any info.

EDIT- woops ... my mistake. Please move to the HVX general news forum ... sorry

 

[Barry_Green]

Very simple -- use the MixPre to take your microphone inputs, and output a line-level signal. Then on the HVX, tell it to receive a line-level signal. That way the HVX's pre-amps are not used at all. And yes, it can increase the overall quality of the sound some. The HVX has very good pre-amps for a camcorder, but a dedicated audio mixer can obviously use better/more expensive components. Somewhere on the forum here MattInSTL did some testing of running mics directly into the DVX, vs. running 'em into a quality mixer and then into the DVX at line level. There was an improvement in the mixer version.

 

[USLatin]

That way the HVX's pre-amps are not used at all.

But they are not by-passed, correct? When the XLR input is set on Line, you are still able to make the level of said signal hotter or lower with the Audio dials in the back of the camera. That leads me to belive that the pre-amp is not by-pased, but instead it is set to where the middle of the Audio dial in the back of the camera gives you 0 dB. whereas switching the inputs to Mic gives you either -50 or -60 dB as set in the menu.
I also am interested in finding the settings that will yeild the least amount of noise being introduced by the HVX's pre amps. It is clear to me that the inputs should be switched to Line, but if the pre-amps are not bypassed, then there might also be a spesific point to which the Audio dials should be left at?

 

[John Froton]

OK .... I think Barry is right on this one and we are a little confused USLatin.

I did some research and found out a little more about what microphone preamps do. In general, the function of a preamp is to amplify a low level signal to line level.

So we are confusing the camera's ability to strengthen the line level signal with doing what a preamp does, which is switch a mic level signal to line level strength.

The ability to adjust the line level signal strength is done by something more of a pot control and is not controlled by a mic level preamp.

I guess we tend to think a preamp would be involved in all amplifying of all signals but in this case the preamps that boost the mic level signal to line level are not related to the volume control of the line level signal.

 

[bbalser]

But they are not by-passed, correct? When the XLR input is set on Line, you are still able to make the level of said signal hotter or lower with the Audio dials in the back of the camera.

Adjusting the "gain" of a signal with the level dials is NOT using the "pre-amp". A pre amp has NOTHING to do with that. The audio signal has a specific strength to it to begin with. A pre amp simply boosts that strength so your recording device can deal with it better, nothing more, nothing less. A pre amp has nothing to do with adjusting the gain of the signal with the level dials. Those are working with the signal strength provided, not adding to it. A pre amp ADDS to the signal, the level dials adjust how much of that provided level you're using.

Think of it this way, the City has a water tower, this is a pre amp. It ADDS pressure to the water line so the water can travel far enough and with enough pressure to get to all the faucets in all the houses around the city. That's the preamp.

At your home, when you turn on your sink, you can use the knob on your sink to allow all of that pressure, or only part of that pressure, to come through the faucet. That's not ADDING anything, only controlling what is already there. That's the level dial on your HVX.

Hope this helps...

 

[John Froton]

Holy cow! Now I am going to have to buy rain gear for the inside of my camera

Just kidding

Thanks for clarifying that.

 

[bbalser]

Yeah, "internal rain gear" is a new catagory of hardware on the B&H web site.

:beer:

 

[ullanta]

OK, look... "preamp" is a fairly general term, and many "preamps" include different approaches to "gain", "trim", "level", etc.

Some preamps do indeed have variable gain; some have fixed gain with a variable trim, etc.

I'm not sure exactly what the circuit topology of the HVX is, but you are certainly NOT "bypassing" all of the preamp functions of the HVX by using an external preamp. What you are doing is making the HVX preamp circuit do as LITTLE of the work as possible, so that it adds the least noise.

The assumption a lot of us work under, which seems to provide the best empirical result, is that the "mid" position of the HVX gain dials neither adds gain nor trims down the levels... that is, the "mid" position makes the HVX audio circuitry do pretty much nothing.

If you can, what you want to do is set your external preamp in such a way that you can use this "mid" setting on the HVX. However, in my experience, this is rarely the case, and I find that some preamps need the HVX to be set for 1/4 past "mid", while others need it to be below "mid" (that is, if you want to use the meters, limiters, and such on your outboard gear. In these cases, the HVX preamp circuitry may be doing a little bit of work, but not the bulk of it.... so the result is still significantly better than using the HVX preamps alone.

As for the semantic issue of "bypassed"... it's a semantic issue. But as you can still add or subtract from the level of the signal... I'd say its not bypassed. Its impact is just reduced. However, if by "preamp" one means ONLY the part of the HVX preamp circuit that gives the major boost from mic to line level, then that is indeed likely bypassed by the mic/line switch. But many external devices that we commonly refer to as "preamps" do indeed have pads and level switches for differing levels of "major" boost that are PART of the larger preamp circuit, and disengaging them does not mean one has bypassed the preamp.

Again, it don't matter... what you want to do on the HVX is keep your gain dials as close to the "mid" setting as possible, to reduce the use of the internal preamp as much as possible.


-Barry

 

[bwest]

Nicely done BenB and good persistence by John Froton and USLatin behalf!

I'm one step closer to understanding this!
Funny how water analogies work for demystifying electricity!