[HiC]

I've got a couple of Marshall MXL 990's going through VTB-1 preamps,
going into an Audigy Platinum EX.

Using the level meter on Soundforge, I find there's about a 25db or so
difference in the noise floor when the mics are connected and phantom
power is on compared to phantom power being on but the mics not
connected. This comparison is at about a 45db gain on the input of the
preamps,(near as I can tell from the calibration markings) output at
unity, and the sound card mixer showing 50% - this seems to yield a
decent signal (peaks at about -10db) when recording individual notes
played on an acoustic guitar at about 8" or so from the mics, with the
mics aimed at about the 12th fret.

I observed these levels with both mics sandwiched between a couple of
pillows which were wrapped in a sleeping bag, inside my homemade sound
booth - sheetrock over 2x4's, R-13 insulation, Armstrong acoustic
panels inside - the point being I don't think sound the mics are
picking up is a significant factor.

Seems to be negligible or no difference whether the phantom is on or
not if the mics aren't actually connected. Btw, I do kill the phantom
before plugging or unplugging the mics.

Given the above, I assume the added noise is from the mics themselves.
This may sound ridiculously obvious, but I want to make sure there
can't be some other issue - something within the preamp that might be
engaged or not, depending on whether the mic is actually connected
regardless of whether the phantom is on. Not likely?

[Scott Dorsey]

HiC wrote:

Using the level meter on Soundforge, I find there's about a 25db or so
difference in the noise floor when the mics are connected and phantom
power is on compared to phantom power being on but the mics not
connected. This comparison is at about a 45db gain on the input of the
preamps,(near as I can tell from the calibration markings) output at
unity, and the sound card mixer showing 50% - this seems to yield a
decent signal (peaks at about -10db) when recording individual notes
played on an acoustic guitar at about 8" or so from the mics, with the
mics aimed at about the 12th fret.

If there is nothing plugged into the preamp, it will be noisy because it
is seeing no source impedance. Try shorting pins 2 and 3 of the mike
input and see how quiet THAT is. That's your actual noise floor.
Having the mike plugged in and the phantom turned off should give you
a similar number.

Then plug in the mike. Note that the mike you are using is one that I
would consider very noisy, but note also that what you're getting is
the room noise plus the microphone noise.

Given the above, I assume the added noise is from the mics themselves.
This may sound ridiculously obvious, but I want to make sure there
can't be some other issue - something within the preamp that might be
engaged or not, depending on whether the mic is actually connected
regardless of whether the phantom is on. Not likely?

Well, you have a fairly noisy preamp with a fairly noisy microphone, so
the end result will tend to be noisy. But who cares? Record something.
Listen to it. If the noise is a problem, do something about it. Odds
are the noise won't be a problem and you shouldn't worry about it.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[HiC]

On Feb 6, 2:53 pm, (Scott Dorsey) wrote:

If there is nothing plugged into the preamp, it will be noisy because it
is seeing no source impedance. Try shorting pins 2 and 3 of the mike
input and see how quiet THAT is. That's your actual noise floor.
Having the mike plugged in and the phantom turned off should give you
a similar number.

Doesn't seem to make much difference. At the same soundcard mixer
levels as previously described, with the preamp disconnected
altogether from the soundcard, makes about 2db difference when
compared to the preamp plugged in, mics hooked up but no phantom.

Then plug in the mike. Note that the mike you are using is one that I
would consider very noisy, but note also that what you're getting is
the room noise plus the microphone noise.

Not much room noise to speak of, per my previous description - sound
booth, plus mics further muffled with pillows and a sleeping bag.


Well, you have a fairly noisy preamp with a fairly noisy microphone,

Doesn't seem to be much debate regarding the mics, but I was under the
impression that this pre was supposed to be considered pretty quiet,
per reviews I've seen.


so the end result will tend to be noisy. But who cares?


Well, me given that I have a specific task in mind.

[Scott Dorsey]

HiC wrote:
On Feb 6, 2:53 pm, (Scott Dorsey) wrote:

Well, you have a fairly noisy preamp with a fairly noisy microphone,

Doesn't seem to be much debate regarding the mics, but I was under the
impression that this pre was supposed to be considered pretty quiet,
per reviews I've seen.

Try comparing with something like a Symetrix 302 if you're looking in
the bargain basement price range.

so the end result will tend to be noisy. But who cares?

Well, me given that I have a specific task in mind.

What is that task, and how much quieter do you want it?

If you're trying to record a clavichord in a quiet hall, this equipment
combination will not be acceptable. Most folks aren't trying to do
that, though.

Use your ears. The meters are nice, but your ears will tell you how
much you really need to reduce the noise. And be aware that the room
noise floor is still probably pretty high compared with even this equipment,
if you are working in a typical home environment.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[HiC]

On Feb 6, 3:58 pm, (Scott Dorsey) wrote:
HiC wrote:

Try comparing with something like a Symetrix 302 if you're looking in
the bargain basement price range.

I appreciate the tip. Obviously you feel it will perform better than
the VTB-1? Will do some inquiring.

[Carey Carlan]

"HiC" wrote in news:1170790396.250019.155530
@m58g2000cwm.googlegroups.com:

I've got a couple of Marshall MXL 990's going through VTB-1 preamps,
going into an Audigy Platinum EX.

Using the level meter on Soundforge, I find there's about a 25db or so
difference in the noise floor when the mics are connected and phantom
power is on compared to phantom power being on but the mics not
connected.

If the input is quiet when the preamp is plugged in but not on, then the
sound card is quiet enough.

Noise increases 25 dB when microphones are attached but muffled in
pillows and sleeping bags. 25 dB is a LOT of noise to add. Have you
looked at the frequency spectrum of the noise? Is it heavily weighted to
treble or bass or is it wideband?

This comparison is at about a 45db gain on the input of the
preamps,(near as I can tell from the calibration markings) output at
unity, and the sound card mixer showing 50% - this seems to yield a
decent signal (peaks at about -10db) when recording individual notes
played on an acoustic guitar at about 8" or so from the mics, with the
mics aimed at about the 12th fret.

45 dB gain is typical for a microphone preamp gain level, so the preamp
volume levels aren't broken.

How much louder is the recording of the music vs the noise level?

I observed these levels with both mics sandwiched between a couple of
pillows which were wrapped in a sleeping bag, inside my homemade sound
booth - sheetrock over 2x4's, R-13 insulation, Armstrong acoustic
panels inside - the point being I don't think sound the mics are
picking up is a significant factor.

Once again, frequency is the key. Your booth and pillows do almost
nothing to curb low frequency rumble.

Seems to be negligible or no difference whether the phantom is on or
not if the mics aren't actually connected. Btw, I do kill the phantom
before plugging or unplugging the mics.

So the phantom power circuit is not adding noise. Is it providing enough
voltage? A voltmeter across pins 2 and 3 should read 48 VDC.

Given the above, I assume the added noise is from the mics themselves.
This may sound ridiculously obvious, but I want to make sure there
can't be some other issue - something within the preamp that might be
engaged or not, depending on whether the mic is actually connected
regardless of whether the phantom is on. Not likely?

You can verify the sound card by playing some generic line level source
like a CD player into the card. It should record clean and quiet.

You can verify the preamp by shorting a 1K resistor across mic input pins
2 and 3. Crank it up. Any noise you get will be preamp plus the tiny
thermal noise of the resistor.

The best way to test your mics is to carry them to a known good system
and plug them in. If they're noisy there, you're done.

Noise is relative. Is it loud enough to interfere with the signal you're
recording? I record noise every day. I just try to keep the signal to
noise ratio high enough (whatever that is).

[Scott Dorsey]

HiC wrote:
On Feb 6, 3:58 pm, (Scott Dorsey) wrote:
HiC wrote:

Try comparing with something like a Symetrix 302 if you're looking in
the bargain basement price range.

I appreciate the tip. Obviously you feel it will perform better than
the VTB-1? Will do some inquiring.

Oh, absolutely. It's basically a cheap SSM2017 chip in a box, but it's
a well-designed layout with a decent power supply. It's sort of the
canonical mid-range console preamp sort of design. Nothing to write home
about, but fairly quiet, effective, and it does the job with no silly
gewgaws or effects.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Richard Crowley]

"Carey Carlan" wrote ...
So the phantom power circuit is not adding noise. Is it providing enough
voltage? A voltmeter across pins 2 and 3 should read 48 VDC.

Actually from pin 1 (ground) to pin 2 should read 48VDC,
and from pin 1 to pin 3 should read 48 VDC. You should
see NO voltage between pins 2 and 3. Minor slip in an
otherwise excelent piece of advice.

[HiC]

On Feb 6, 7:06 pm, Carey Carlan wrote:

Noise increases 25 dB when microphones are attached but muffled in
pillows and sleeping bags. 25 dB is a LOT of noise to add. Have you
looked at the frequency spectrum of the noise? Is it heavily weighted to
treble or bass or is it wideband?

Running spectrum analysis on one recording of "air" in the room shows
"prominent frequency -79 db at 47hz" I got another that indicated -80
db at 22hz. While not exactly clear how this is arrived at as a
"prominent frequency", I gather it's pointing at the low frequency
end?

Apparently you're correct. I find that just by engaging the 70hz
rolloff switch, it drops the noise floor by about 5db. Fooling with eq
drops it even more. This seems promising. I'll be curious to see how
close I can get toward my goal just by tweaking the eq & optimizing
mic placement.

[Carey Carlan]

"Richard Crowley" wrote in
:

"Carey Carlan" wrote ...
So the phantom power circuit is not adding noise. Is it providing
enough voltage? A voltmeter across pins 2 and 3 should read 48 VDC.

Actually from pin 1 (ground) to pin 2 should read 48VDC,
and from pin 1 to pin 3 should read 48 VDC. You should
see NO voltage between pins 2 and 3. Minor slip in an
otherwise excelent piece of advice.

Yup. I should never discuss terminating resistors and phantom voltages in
the same message.

[Carey Carlan]

"HiC" wrote in
oups.com:

On Feb 6, 7:06 pm, Carey Carlan wrote:

Noise increases 25 dB when microphones are attached but muffled in
pillows and sleeping bags. 25 dB is a LOT of noise to add. Have you
looked at the frequency spectrum of the noise? Is it heavily
weighted to treble or bass or is it wideband?

Running spectrum analysis on one recording of "air" in the room shows
"prominent frequency -79 db at 47hz" I got another that indicated -80
db at 22hz. While not exactly clear how this is arrived at as a
"prominent frequency", I gather it's pointing at the low frequency
end?

Apparently you're correct. I find that just by engaging the 70hz
rolloff switch, it drops the noise floor by about 5db. Fooling with eq
drops it even more. This seems promising. I'll be curious to see how
close I can get toward my goal just by tweaking the eq & optimizing
mic placement.

This is typical and harmless. Unless you're recording something really
deep like bass violin or organ, you can roll off everything 47 Hz and
below. Likely culprits are your furnace, refrigerator, traffic, low flying
helicopters, etc. which are gently shaking your house.

My "rule of thumb" bass rolloff is an 8th order Butterworth filter below 64
Hz.

In fact, you'll want to start your high pass filter higher. I edited a
concert this week of ladies' chorus singing a capella (no instruments) with
a rolloff at 140 Hz. As long as you leave the fundamental of the lowest
note, you're usually OK.

[Scott Dorsey]

HiC wrote:

Apparently you're correct. I find that just by engaging the 70hz
rolloff switch, it drops the noise floor by about 5db. Fooling with eq
drops it even more. This seems promising. I'll be curious to see how
close I can get toward my goal just by tweaking the eq & optimizing
mic placement.

You got the air conditioning turned off and all the appliances shut down?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[[email protected]]

On Feb 6, 4:58 pm, (Scott Dorsey) wrote:
HiC wrote:
On Feb 6, 3:58 pm, (Scott Dorsey) wrote:
HiC wrote:

Try comparing with something like a Symetrix 302 if you're looking in
the bargain basement price range.

I appreciate the tip. Obviously you feel it will perform better than
the VTB-1? Will do some inquiring.

Oh, absolutely. It's basically a cheap SSM2017 chip in a box, but it's
a well-designed layout with a decent power supply. It's sort of the
canonical mid-range console preamp sort of design. Nothing to write home
about, but fairly quiet, effective, and it does the job with no silly
gewgaws or effects.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Not SSM2017 anymore in the Symetrix 302. It's been an INA103 for about
15 months according to my neighbor that works at Symetrix. I have one
here with the INA103 and it's pretty darn decent sounding.

bobs

Bob Smith
BS Studios
we organize chaos
http://www.bsstudios.com

[Scott Dorsey]

wrote:
On Feb 6, 4:58 pm, (Scott Dorsey) wrote:
Oh, absolutely. It's basically a cheap SSM2017 chip in a box, but it's
a well-designed layout with a decent power supply. It's sort of the
canonical mid-range console preamp sort of design. Nothing to write home
about, but fairly quiet, effective, and it does the job with no silly
gewgaws or effects.

Not SSM2017 anymore in the Symetrix 302. It's been an INA103 for about
15 months according to my neighbor that works at Symetrix. I have one
here with the INA103 and it's pretty darn decent sounding.

That's good news. The INA103 is a pretty slick device. Interestingly
enough, it sounds better when it's operating at the highest gains possible
since most of the distortion is low-level nonlinearity on the differential
output stage. I think that's probably a good compromise.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Richard Crowley]

"Scott Dorsey" wrote ...
wrote:
(Scott Dorsey) wrote:
Oh, absolutely. It's basically a cheap SSM2017 chip in a box, but it's
a well-designed layout with a decent power supply. It's sort of the
canonical mid-range console preamp sort of design. Nothing to write
home
about, but fairly quiet, effective, and it does the job with no silly
gewgaws or effects.

Not SSM2017 anymore in the Symetrix 302. It's been an INA103 for about
15 months according to my neighbor that works at Symetrix. I have one
here with the INA103 and it's pretty darn decent sounding.

That's good news. The INA103 is a pretty slick device. Interestingly
enough, it sounds better when it's operating at the highest gains possible
since most of the distortion is low-level nonlinearity on the differential
output stage. I think that's probably a good compromise.

Are the THE chips being used in any commercial equipment yet?
Or are they even in full production yet?

[Scott Dorsey]

Richard Crowley wrote:

Are the THE chips being used in any commercial equipment yet?
Or are they even in full production yet?

The THE transistor arrays are used in a bunch of discrete preamps. I
don't know if the 1510 has been used in anything commercial yet.

The 1510/1512 are in full production and available from Mouser.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[HiC]

On Feb 7, 9:49 am, (Scott Dorsey) wrote:
HiC wrote:

Apparently you're correct. I find that just by engaging the 70hz
rolloff switch, it drops the noise floor by about 5db. Fooling with eq
drops it even more. This seems promising. I'll be curious to see how
close I can get toward my goal just by tweaking the eq & optimizing
mic placement.

You got the air conditioning turned off and all the appliances shut down?

A/C is off, as well as the breaker box next to the air handler -
already went through that drill a while back trying to figure out what
gear was making the faint buzzing noise.

The refrigerator being on or not doesn't seem to make any difference,
it's 2 rooms away - the sound would have to go through 2 walls plus
the sound booth wall which is built exactly the same way as the house
walls.

[Scott Dorsey]

HiC wrote:

The refrigerator being on or not doesn't seem to make any difference,
it's 2 rooms away - the sound would have to go through 2 walls plus
the sound booth wall which is built exactly the same way as the house
walls.

It doesn't go through the walls... it vibrates the floor, then the floor
under the mikes vibrate. Low frequency sound is VERY readily conducted
through the building structure. That's much of what makes commercial
studio rooms so expensive to build.studio rooms so expensive to build.
You may not even hear it, but put your fingers out and lightly rest them
on a tabletop and see what you can feel.

Good shockmounting can reduce the problem, but it won't eliminate it.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[HiC]

On Feb 8, 9:16 pm, (Scott Dorsey) wrote:

It doesn't go through the walls... it vibrates the floor, then the floor
under the mikes vibrate. Low frequency sound is VERY readily conducted
through the building structure. That's much of what makes commercial
studio rooms so expensive to build.
You may not even hear it, but put your fingers out and lightly rest them
on a tabletop and see what you can feel.

Whatever the refrigerator may be putting out isn't registering on the
level meters - i.e. plugged in and running or unplugged makes no
difference in the highest level recorded when recording ambient sound,
so in this case it doesn't appear to be a significant factor.

Both mics are shock mounted and of course, the stands are sitting on
carpet and padding, whatever added benefit that is.

So, a "floating" floor really makes a big difference?

About what frequency range is considered low frequency noise that
you're referring to?

[Scott Dorsey]

HiC wrote:

Whatever the refrigerator may be putting out isn't registering on the
level meters - i.e. plugged in and running or unplugged makes no
difference in the highest level recorded when recording ambient sound,
so in this case it doesn't appear to be a significant factor.

Okay, that's good.

Both mics are shock mounted and of course, the stands are sitting on
carpet and padding, whatever added benefit that is.

That's good also.

So, a "floating" floor really makes a big difference?

Absolutely. Cars drive by outside, nothing happens inside. Drum kit
plays in one room, you can hardly hear it in the next.

About what frequency range is considered low frequency noise that
you're referring to?

Say 5 Hz to 30 Hz or so. Sometimes lower. I believe that microphone doesn't
have really extended low end, though, which helps a lot.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."