Mic pre-Amps noise floors

[Gaston69]

I would like to know if a mic pre-amp manufacturers use the same kind of measuring the mic pre-amp noise floor, because I see adverts for "clean" pre-amps with S/N Ratio of -120dB and see also Gearslutz respected manufacturers advertising with -91dB S/N Ratio.

Would a -91dB so much more noisier then the -120dB?

I've done lately a recording using DPA 4006 with an Amek DMCL had lot's of noise and cannot find where the noise is comming from, gain was set at 54dB.

Gaston

[mosrite]

The Amek preamps have a solid reputation for being quiet and clean so I would be suprised if it's that.

[ahjteam]

If the noise becomes an issue, record the vocals normally, then add a new track and just record the silence with same settings, then flip the phase from it, it should cancel out majority of the noise off.

[aussie_techie]

its usually best to look at the EIN (equivalent input noise) not just the S/R
for anything needing alot of gain with low noise i would be looking for an EIN of a pre of at most -128db

what were you recording? 54db gain seems like alot for a 4006. last time i used a pair of 4006 was with a small orchestra and only needed 25db gain.

with 4006s and an Amek you noise shouldn't be a problem, maybe start by checking your cables

[klaukholm]

The 4006 will amplify any room noise you have. If there is a hum in the lights or aircondition, or a computer/fanned device running it will certainly come out at 50+db gain.

Other than that it could be the, mic cables, capsules.
Did you use the ad's on the amek?

[andy_simpson]

Originally Posted by Gaston69

I would like to know if a mic pre-amp manufacturers use the same kind of measuring the mic pre-amp noise floor, because I see adverts for "clean" pre-amps with S/N Ratio of -120dB and see also Gearslutz respected manufacturers advertising with -91dB S/N Ratio.

Would a -91dB so much more noisier then the -120dB?

I've done lately a recording using DPA 4006 with an Amek DMCL had lot's of noise and cannot find where the noise is comming from, gain was set at 54dB.

Gaston

How loud do you monitor? This can have a big effect on the perception of noise floor.

Andy

[Alexey Lukin]

Originally Posted by ahjteam

If the noise becomes an issue, record the vocals normally, then add a new track and just record the silence with same settings, then flip the phase from it, it should cancel out majority of the noise off.

It should only increase the noise level by 3 dB.

[John Brook]

According to DPA, the specs on the 4006 48v version are: "Equivalent noise level A-weighted: Typ. 15 dB(A) re. 20 µPa (max. 17 dB(A))" This is noisier than a large diaphragm mikes you may be used to, which have noise spec more in the 9 - 12 db range. DPA's 4041 is: "Equivalent noise level A-weighted: Max. 8 dB(A) re. 20 µPa."

I find that when I'm recording choral groups, I need a ton of clean, clean, clean gain, because youth choirs are just not that loud. Student orchestras are less demanding; bands put out plenty of sound. Remember that sound pressure falls off 6db every time you double the distance to the sound source, so try to mike as close as you can and still achieve good blend.

[kwesloh]

Originally Posted by John Brook

According to DPA, the specs on the 4006 48v version are: "Equivalent noise level A-weighted: Typ. 15 dB(A) re. 20 µPa (max. 17 dB(A))" This is noisier than a large diaphragm mikes you may be used to, which have noise spec more in the 9 - 12 db range. DPA's 4041 is: "Equivalent noise level A-weighted: Max. 8 dB(A) re. 20 µPa."

I find that when I'm recording choral groups, I need a ton of clean, clean, clean gain, because youth choirs are just not that loud. Student orchestras are less demanding; bands put out plenty of sound. Remember that sound pressure falls off 6db every time you double the distance to the sound source, so try to mike as close as you can and still achieve good blend.

I've used the 4006s on hundreds of live recording with many different Mic Pres and the self-noise of the mics has never been an issue. They are extremely revealing and I would agree with a previous posters that the probable culprit is ambient noise. Please don't place your mics with the intention of making your recording less noisy. Put the mics where they sound good. Period. I did a gig a few years ago at a respected studio and the chief engineer said he wanted to get rid of his 4006s because they sounded 'boxy' It seemed especially suspicious given that both mics had the same "problem" As it turns out the 4006s were the only mic in his collection that captured the 'boxy' sound of his studio accurately (not to mention the HVAC and low-flying aircraft)
Good luck with this.
Kyle

[Martin Kantola]

Originally Posted by ahjteam

If the noise becomes an issue, record the vocals normally, then add a new track and just record the silence with same settings, then flip the phase from it, it should cancel out majority of the noise off.

What a bunch of crap!

Martin

[Testing123]

Originally Posted by ahjteam

If the noise becomes an issue, record the vocals normally, then add a new track and just record the silence with same settings, then flip the phase from it, it should cancel out majority of the noise off.

Huh? You're assuming the noise from both tracks will be phase coherent, which I don't think will be the case. I think that technique will make the noise worse.

[rufus13]

Originally Posted by ahjteam

If the noise becomes an issue, record the vocals normally, then add a new track and just record the silence with same settings, then flip the phase from it, it should cancel out majority of the noise off.

What you might be thinking of is a differential microphone that rejects acoustic noise that hits both microphones (Desired source sings/talks/plays into one microphone). Noise, by its' nature, is random and will not cancel (using your description, because the event is different, at a different time). On the other hand, steady tones or cyclic events may be possible to suppress in a DAW using inversion/cancellation, along with gating, EQ notching, and manual waveform re-drawing. It's common to prefer the version with noise over the gnawed-on "clean" post-production version.

Better to find and kill the offending noise before recording than attempt a post-production fix.

Cheers.

[nosebleedaudio]

Noise measurements can be confusing..
Most mics quote noise "A" weighted, so you're comparing apples with apples.
The problem with pres as a comparison is some quote noise "A" weighted filter, others 22 to 22kHz bandwidth.
The numbers will be several db apart, the "A" filter giving a lower or better looking number.
And as stated above ambient noise will be higher than most pres...
This is one of the main reasons a real studio needs quiet rooms...

[ghellquist]

Originally Posted by Gaston69

I've done lately a recording using DPA 4006 with an Amek DMCL had lot's of noise and cannot find where the noise is comming from, gain was set at 54dB.
Gaston

There are several probable sources. You will need to verify each of them, perhaps by borrowing or renting equipment to compare with.

room noise - this is according to my guess the most probably source. All rooms has noise in them, more or less. The room noise becomes an issue if what you are trying to record has a low volume and is far away. Possible ways around it may be to

• get closer - closer gets a better ratio between noise and source
• change to a directional mic - the difference is not quite as large as can be expected, but it can make enough of a difference

microphone - microphones have different inherent noise. The noise comes partly from the electronics in the mic, partly from the air molecules impinging on the mic. A larger mic membrane has a better ratio between "air noise" and the sound we are trying to mic. In this case, with a professional quality mic, the electronics is not an issue, but it could be with some cut-price mics. Going for a larger diameter mic will decrease the noise here, and probably give you a stronger signal that needs less amplification in the mic preamp. Personally I do not think the 4006 is the problem. They are avesome mics, but not necessarily the first choice for every situation.

mic preamp - all mic pre amps adds noise. Some more some less. Do try to test a different amp and see if could have an effect. Again the Amek may not be the culprit.

sound card - all sound cards adds noise. Some more, some less. In classical recording I generally want a bit of headroom, so my peaks may be around -12dB. RMS may be down at -50dB FSA in softer passages. Each bit of digital is roughly 6dB, so we might be eating margin here. And most sound cards gives from 16 to at most 20 bits of true precision, regardless if they are marketed as 24bit. Check the S/N ratio on the sound card, many end up around 96dB, ie around 16 bit. And if your source is down at -50 dB you are rapidly eating the noise margin here. Some sound cards has switchable input sensitivity and might be noiser in one setting then in a different one.

There are a few ways to mess things up that may add noise. One is if you inadvertantly goes from balanced outputs to unbalanced inputs. This will eat amplification, which you need to compensate in some other place.

Regardless, do try (rent, borrow) other equipment to find what works best for you.

Gunnar