What pre-amp really does

C

c3kings

Well-known member
Dear All,

I heard a lot about the importance of pre-amp. For example, people will say that getting a mixer is crucial becasue it has a better pre-amp than the one in your camcorder.

But to be honest, being ignorant, I don't really know what pre-amp does in the whole recording process. My only understanding is that pre-amp is the thing to give the electricity to the mike (maybe I am wrong).

I know it is not a forum of audio engineering, but at least, I want to be able to explain to people more than, "well, it is just a better pre-amp."

Thanks a lot in advacne.

King
 
the preamp is amplifying the small signal from your mic to these levels your mixer or recorder need .
good preamp stand for low noise , ability to pass and amplify wide fq spectrum ,good linearity , be able not to clip on wide range of signals
every preamp colorize the sound in different way what may or may not be pleased by your ear , thats why there are so many different companies which produce these .
 
A preamp amplifies the signal from the microphone. Why would you want to do that?

The object is to amplify the actual mic signal so it is "louder" than any noise already in the system...from cables, electronic circuits, cosmic rays, whatever...so the difference between the "noise floor" and the signal is greater.

Without a preamp, the difference may be 40 dB. With a preamp, the difference may be 60 dB. (numbers made up to illustrate the concept...the difference can be a lot higher than that)

What you want in a good preamp is one that will amplify the signal it receives without adding any more noise of its own, and without "coloring" the signal.

The preamps in the DVX are good. Using an outboard preamp/mixer can still be a good idea because htting the DVX with a "hotter" signal means you don't have to turn the gain up on the DVX....the higher the gain setting, the more noise you may get. It's almost always better to keep things more toward their mid-range than the higher end.

I probably made a hash out of that explanation. Someone will correct me if I screwed up. :)
 
To Pre-Amp or not to Pre-Amp

To Pre-Amp or not to Pre-Amp

c3kings said:
Dear All,

I heard a lot about the importance of pre-amp. For example, people will say that getting a mixer is crucial becasue it has a better pre-amp than the one in your camcorder.

King
Click to expand...

Hi King,

Who are those "people" anyway? They sound a bit conceptual to me. It's not as though cameras have extra input jacks beyond the internal pre-amp that allow you to bypass it. If that were the case, then yes, an argument might be made that an external super-duper pre-amp might provide better fidelity. But since an external pre-amp is *ADDED* in the serial chain, you're still going through the internal camera pre-amp. So under normal circumstances, you can't improve the fidelity of the incoming signal by adding yet another piece of gear.

Now then, if the camera's pre-amp provided 60db Signal to Noise and only fair distortion characteristics with a low input signal from a dynamic mic, then indeed processing the signal with an external pre-amp that has 80db S/N and ultra-low distortion might be justified. But this is an extreme example which I doubt your "people" are quoting since it would depend on a specific (an unusual) situation.

Regarding coloring the the signal, back in the olden days amplifiers used vacuum tubes. Among other things, the tube amps would generate secondary audio output signals that were a low amplitude frequency multiple of the original frequency (harmonics). Actually, a small amount of harmonic distortion can sound pleasant to the ear. With the advent of better transistor technology, harmonic distortion was essentially wiped out but many audiophiles complained the signal didn't sound as pleasing to the ear. That's where the coloring comes in and why antiquated vacuum tube amplifiers are still being sold today. In fact, some high-end transistor-based pre-amps have harmonic distortion circuitry to simulate vacuum tube harmonics.

Finally, a mixer allows you to do a multitude of other things to process the signal, but then we're outside the pre-amp discussion.

Hope that clears things up a bit.

Regards, Michael
 
moonlitnite said:
Hi King,

Who are those "people" anyway? They sound a bit conceptual to me. It's not as though cameras have extra input jacks beyond the internal pre-amp that allow you to bypass it. If that were the case, then yes, an argument might be made that an external super-duper pre-amp might provide better fidelity. But since an external pre-amp is *ADDED* in the serial chain, you're still going through the internal camera pre-amp. So under normal circumstances, you can't improve the fidelity of the incoming signal by adding yet another piece of gear.


Regards, Michael
Click to expand...


By using an external microphone preamp, you are in fact bypassing the cameras internal preamplifier (when you switch the inputs to line level). I don't have schematics for the camera, but I would argue that in line mode, the level pots on the camera only function to attenuate the signal.

I posted a little example about a year ago that highlighted just this comparison, and I believe most people agreed they could hear a difference. The biggest improvement was using a high quality external preamp. Using an external recorder was also another step up in quality, but not really as obvious, at least in my opinion.
 
most of the high end cameras such Sony 900,900r , digi beta , xdcam do by pass the preamp so you actually have better external one , not to mention part of then can be bypassed all the analog stage and go directly digital (xdcam 900r , 900and digi beta on channels 3 and 4)
dont really know if the panasonic works this way or not but it really doesnt matter as long what i get with my mixers sounded better then what i get with direct microphone .
 
Tigeba and Oleg,

Right Tigeba, I definitely agree if it's a pro-sumer+ camera with line level inputs, it should be bypassing the preamp. And even better, Oleg, if you can digitally record with an external device using high bit-per-second/high sampling rate gear (mixing in the NLE). The 64kbps camera audio certainly isn't in the same league as a 384kbps digital recorder.

Regards, Michael
 
Thank all of you giving me such an important lesson.
I learn a lot from this forum, AGAIN!
Actually, do you think we can write an email to ask Panasonic to verify if the line-in in fact bypass the camera internal pre-amp? Anyone has their enginners' email address? I don't mind to write to them.
Now that I realize more the importance of pre-amps, is there any suggestion for me which pre-amps (or mixer) are good.
In fact, I am planning to get a SD302, so is there any alternatives that you may suggest around this price range.
At home, I do have two Mackie mixers (12 &16 channels), but they are not appropiate to be used as my documentary location mixer. By the way, do you know if anyone using this kind of mixer for, say, feature film?
Thank you very much.
King
 
moonlitnite said:
Tigeba and Oleg,

Right Tigeba, I definitely agree if it's a pro-sumer+ camera with line level inputs, it should be bypassing the preamp. And even better, Oleg, if you can digitally record with an external device using high bit-per-second/high sampling rate gear (mixing in the NLE). The 64kbps camera audio certainly isn't in the same league as a 384kbps digital recorder.

Regards, Michael
Click to expand...

It is a very interesting idea. So, we are recording at 20 or 24 bit and edit with it, and at last output it back to 16bit 48hz to tape. Anyone has done this workflow? Does it sound better?
Thanks.
King
 
Bad news. SD 302 is out of stock in my area, and SD doesn't let B&H to ship it internationally.
Any suggestion besides SD?
Thanks.
King
 
moonlitnite said:
Hi King,

Now then, if the camera's pre-amp provided 60db Signal to Noise and only fair distortion characteristics with a low input signal from a dynamic mic, then indeed processing the signal with an external pre-amp that has 80db S/N and ultra-low distortion might be justified. But this is an extreme example which I doubt your "people" are quoting since it would depend on a specific (an unusual) situation.


Regards, Michael
Click to expand...

As others pointed out most decent cameras (we are on a DVX user forum) have line inputs. In fact a number of very low end consumer ones do also. The Sound Devices Mix Pre has something like a 116dB S/N, most really good preamps are in the same range.
 
c3kings said:
It is a very interesting idea. So, we are recording at 20 or 24 bit and edit with it, and at last output it back to 16bit 48hz to tape. Anyone has done this workflow? Does it sound better?
Click to expand...

It depends how much processing you're going to do. As you often don't know that until you get to post, many folks prefer to have the higher bit depth to work with if possible. It's like recording video in 4:4:4 even if you know you're only outputting it to DVD.
 
Having greater bit depth gives some leeway in setting the levels and makes life easier for the recordist. The quality difference can not be heard, though*.

Using higher sampling rates is a waste of storage space, unless you have some super mics extending to 40kHz and you plan to slow down the audio fourfold.

*) I have read about many tests where super audio or straight analog signal was compared to 16/44.1 digital audio and in none of those tests the sucjects could distinguish between the two. Thus 16/44.1k or 48k is plenty good enough for final output.
 
GenJerDan said:
It's almost always better to keep things more toward their mid-range than the higher end.
Click to expand...

Is this really the best setting? or should we go a tad lower?
I found myself automatically wanting to turn the gain down one point
from the middle as soon as I got my HVX... Was I getting an actuall
lower in-camera per-amp lower noise or simply making it harder for me to hear the noise?

With my Sound Devices MM-1 comming this Tuesday, will I benefit from even lower on-camera
settings and raising the signal with the MM-1? What settings would you recommend?

Oh! wait...

tigeba said:
By using an external microphone preamp, you are in fact bypassing the cameras internal preamplifier (when you switch the inputs to line level). I don't have schematics for the camera, but I would argue that in line mode, the level pots on the camera only function to attenuate the signal.
Click to expand...

So should I set the XLR input on the camera to "Line" and I'll be actually by-passing
the in-camera pre-amp?
 
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moonlitnite said:
Tigeba and Oleg,

Right Tigeba, I definitely agree if it's a pro-sumer+ camera with line level inputs, it should be bypassing the preamp. And even better, Oleg, if you can digitally record with an external device using high bit-per-second/high sampling rate gear (mixing in the NLE). The 64kbps camera audio certainly isn't in the same league as a 384kbps digital recorder.

Regards, Michael
Click to expand...

why is that , the same bit rate was used with dats for high end at least 15 years - so what did change sudenly - nothing
if i can record to the camera i just save every one money
good enouth for me and most of the producers i work ( 250000us $ comertials and 500000 feuters films , no one ask for double if there no need .
by the way i oun 2 744 which also bring some bread :-))
 
I just called Panasonic and the tech I got wasn't able to tell me what would be the best setting for the Audio level to minimize the noise added by the in-camera pre-amps... he also said that by setting the XLR input to Line you are not bypassing the pre-amp, just setting the camera to expect a different level of a signal commonly out of mixers and other "devices" as supposed to the level it would expect to come out from a Microphone... He also said that this was the first time he's heard of anyone using a pre-amp like this! I guess everyone goes straight to table mixers porta-brace bags full of stuff or a 302... did I mess up by getting the MM-1?


Oleg, I see u r home today, please help me! You and a few others helped me pick my initial items I'll feel so much better if you reply.

do you guys know if there would be noise added from the in-camera pre-amp by setting the channel level too low?
once again, what do you think would be the settings on my Sound Devices MM-1 and on the camera that would be most likely to yield the least noise?
 
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dont be histirical :-) no body really would know ,
i never liked the dvx audio chain to much and if the technitian is right about that the line level is just another 40 db pad i wouldnt besurprise at all .
for regullar work it is more then fine , for cinema relies i wouldnt go stright to dis camera , for tv - it is serving about 1/3 of the shows shown on israely tv .
so if youy set the levels right and dont push your luck to ioverlloqad the input stage you may be will survive ,
about the technition that doesnt know people use external preamp and mixerr with that camera i wouldnt be surprise he may be dont know if it passing or not , ill try to find the schems next week really answer that stupid question .
.
the external gain / limmiter control would be better solution to get the right level , so my sudgestion go what was already invented :-)
 
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