What Is The Purpose Of A Mic Preamp?

  • Thread starter Thread starter anppilot
  • Start date Start date
anppilot

anppilot

Never Act Like U Know All
Hey Gang. Not to sound ignorant, but I'm mainly a MIDI person. I am somewhat new to recording vocals and acoustic instruments. Always using line level inputs, I havent been to concerned about using "preamps", "phantom power" and all that stuff. I can say I do know this: I was given a (what I am told) is a $700 Sony stereo mic used for studio production, live, and many other uses. The person who gave it to me is a friend of the family who does audio/video for conventions, and stuff like that (so in my opinion, he knows his stuff... but he could be bs'ing me for all I know). Anyway, it has a battery pack that came with it I believe its incase you have a board that doesnt have Phantom Power. So, Im not using the battery pack thing cause my Tascan TMD-1000 has Phantom pwr built in. Using Cubase VST for my recording medium, I have only recorded one person with this new mic, without a preamp, and it sounded GREAT! Clean, warm, no distortion, and very rich. I have talked to a couple and they say that you should use a mic pre. Someone please explain in laymans terms how a Preamp would benefit my recordings.

Sincerely,
Mike
 
The use of an external mic pre is to bypass the (usually cheap) mic pres built-in to most consoles/mixers at price points less than the Neves or SSLs!! (Which is pretty much ALL of them - analog or digital)

Unless you're recording a large number of tracks at one time, the idea is to get 1 or 2 high-quality mic pres, giving you 1-2 channels of high-quality signal path - avoiding the considerably cheaper electronics in your boards pres. (You patch the output of your pre directly to your recording device, bypassing your mixer).

Your sound quality improves immeasurably (unless you buy a cheap mic pre - which ends up being no better than what's already on your board!)

Hope this helps...

Bruce Valeriani
Blue Bear Sound
 
basically you're already using decent preamps-- in your mixer.
i suspect that "sound quality improves immeasurably" with other preamps means that basically you can't hear the difference.
the amount of noise generated by your preamp is probably negligible compared to the mic noise.
unless you want to add some nice tube "warmth" (distortion)...
 
A real pre will change your mind about what is possible mixing multiple tracks.
 
panang said:
basically you're already using decent preamps-- in your mixer.
i suspect that "sound quality improves immeasurably" with other preamps means that basically you can't hear the difference.
the amount of noise generated by your preamp is probably negligible compared to the mic noise.
unless you want to add some nice tube "warmth" (distortion)...

You obviously haven't heard a good mic combined with a good mic pre for you to say that..

Bruce Valeriani
Blue Bear Sound
 
ok, but the guy's already got a really cool mixer that not only has nice preamps but also built-in 24-bit A/D, all at 100dB SNR from mic inputs to digital output. If anything the mixer is better than the mic.

i have to admit i don't have any experience with multi-thousand dollar preamps though. i'm trying to understand why it would make a difference... maybe you can set me straight:

his mixer claims to deliver 100dB signal to noise ratio from mic input to digital output -- actually this is a little unclear what that's referenced to, but probably it's 25dB below the max 24-bit signal, which gives a dynamic range of 125dB.(http://www.tascam.com/spec_Mixing_Consoles.cfm)

now granted it is possible to find a preamp with greater signal to noise: for $1500 list you can get a mic preamp that delivers a nominal 128dB signal to noise ratio. sweet jezeus. (http://www.sascom.com/laf_lp21.html)

but what signal to noise does the microphone deliver? His mic probably has a noise floor at about 20dB SPL. to get 128 dB S/N out of the microphone, you signal would have to record at 148dB SPL, which is beyond the human threshold of pain. now probably the upper limit for his mic is 130dB SPL anyway. so in practice, to have 25dB headroom he can only record at 105dB SPL. this yields a SNR of about 85dB.

now i am claiming that a preamp with 128dB SNR is a waste of money because the noise floor of the preamp is 43dB below the noise floor of the microphone!

because of how the ear works, you cannot hear any noise that is more than 6dB below another one in a given frequency band: it's masked (the key principle of MP3 compression). Let's use 12dB to make absolutely sure-- i know some of you recording engineers have extra sensory hearing. either way the preamp noise is masked by the mic noise. in fact, with this mic, you could raise the noise floor of your 128dB SNR mic preamp by 31dB (43dB - 12dB) before any human ear could hear the difference.
in other words, for this mic, a preamp with 97dB SNR is just as good as one with 128dB SNR, all other things being equal, and is surely far cheaper. (and i don't even want to talk about the sound card... )

so help me out boys, where have i gone astray?
is it that noise is not really the issue with expensive mic preamps? what is the issue then? frequency response? distortion? karma? dogma? i must be missing something.
 
It's not just a question of noise... it's the quality of the electronics inside, the frequency characteristics of the interaction of the mic and the pre, accuracy of the signal chain...

It's everything that makes the difference between any sound equipment at the multi-thousand dollar level versus anything else at a lower price point. Just look at a basic 8-channel analog mixer for say $1000 - it needs 8 pres in it - they gotta use the basic, cheap op-amps everyone else uses to meet that price point... with that single cost-cutting measure you've started to mess with your sound. Maybe the that one component doesn't add that much noise on it's own... well, it's an 8-channel board so multiply that noise level by 8... ooops we've buggered the sound again!!! Now add op-amps for the busses, bring it up from 8 channels to 24-channels, 8-busses, auxes, etc... you get the idea.

What started as tiny distortion at the front of the signal chain now has multplied many times by the time the signal hits your mixers output...

Geddit???

I'm not saying you can't make stuff sound good with cheaper gear - you can, but you have to work on it and know how to deal with the limitations inherent in the cheaper gear. One of the best ways is bypass the built-in pres, and use a high-quality external - direct to tape - bypassing the board completely!

Bruce Valeriani
Blue Bear Sound
 
that makes sense.
my main point is just that the signal is at very least as good as [oops, i mean: no better than] the pathway's weakest link, so if you're going to throw down money, it's best to spend it on the worst component.

so would you look at total harmonic distortion (THC) as the most important factor, when looking at specs?

p.s., just wanted to correct some misstatements

for the tascam--- i was looking at the tm-d4000 specs.
the tm-d1000 says 80dB SNR.
and the THD is >.1% -- not so hot.

for the lafont-- actually the 128 SNR is mislabeled-- what they really mean is -128 equivalent input noise (EIN).
so SNR is probably more like 100dB..
doesn't say about THD













[Edited by panang on 09-17-2000 at 14:07]
 
I own the TM-D1000, so how much would you say the pre-amps included are worth? I want to know this so I can decide what my price range would be if I wanted to buy a pre-amp.
 
TO be honest - I think specs are essentially useless in trying to determine what the sound quality will be... Sure you can make some estimated guesses, but what really counts is LISTENING....

Spec sheets are usually written by the marketing department after chatting for a few seconds with the component designer. They're also there for the engineers to argue about...

Marketing person to engineer:
"...so you say noise level is -90db, that's almost -100db... wow!"
What ends up in the manual:
"...s/n ratio approximately -100db..."

Engineer 1 to engineer 2:
"... yeah John, saw your specs yesterday - gimme a break - I acheived that LAST year..."

I'm exaggerating, of course for the sake of my point, but bottom line is specs can easily mislead - if you have a good set of ears however, you won't be misled...

SO... throw your specs out - you wanna know what a mic sounds like thru your board, beg borrow or steal one and plug it in and TRY IT! Is it noisy? Is it clean?? Does it sound like what's going into it or is it brittle/honky/dull???

When you buy an effect - take it home, plug it in and REALLY LISTEN - does it sound cheesy or fake (reverbs) - do you hear noise/distortion/etc... if you don't like it make sure you buy from stores that let you return it if it doesn't suit you... and don't buy from the ones that don't have that kind of policy.

My opinion... take it for what it's worth... (about 2 cents Cdn - 1 cent US!!) :)


Bruce Valeriani
Blue Bear Sound


[Edited by bvaleria on 09-17-2000 at 07:36]
 
when you're buying stuff on the web, though, you basically have just the specs and random bits of hearsay.
(so maybe one shouldn't do that, i don't know)
at least the specs are objective, even if there is some innaccuracy. 100dB SNR preamp is going to sound better than 80dB, other things equal (but only if your mic and sound card are good enough).
 
I Think

I think panang is a little too stuck on specs... Sorry panang, I just had to say it.
 
Yes... WAY too hung up on spec... ask for people's opinion on this forum... ask at RAP (rec.audio.pro)... hey wait here's a novel idea - go to a retailer and TRY IT!!!!

:)

Bruce Valeriani
Blue Bear Sound
 
no, you're right, i am hung up, but i didn't get there by myself.... i'm doing research, and i have to justify the equipment i use .. one can't write in a grant proposal, that some guy on a BBS named "recording engineer" says these $2000 XYZ preamps are tops (and that i need to use them with my $400 dollar sound card and my $100 microphones.. but that's another story;)
in research, hearsay just doesn't cut it. a listening test is important, but still too subjective. to use human listeners i'd have to run an experiment with 20 people or so... with every combination of equipment... a whole project in itself.

so what i'm basically trying to do is find out from you guys which specs (besides the price!) best predict the audio quality... so that i can match the quality of my preamps with that of my microphones and sound card...
 
Ahhh.. now it's clear (why you put so much stock into the specs), but I think you'll have yourself a problem anyways - the truth is - the specs DON'T tell you the story - only hints. Some of the most highly regarded (now vintage) microphones had pretty horrible specs, but it was their sound characteristic that made them well-liked....

It's like that with a lot of equipment... Put 2 pieces of gear side-by-side - specs up the ying-yang - and ask 2 engineers which they prefer... one'll say A - it's so much warmer-sounding, and the other'll say B - no way, mine doesn't sound muffled....

You may need to find another way to qualify your gear purchases...

Bruce Valeriani
Blue Bear Sound
 
Back
Top