[Sursound] Re. Re: Re Re: Ambisonic Mic Comparison

[Enda Bates]

Hi Sampo,
well the objective directional analysis we're discussing here was not of course, but yeah all of the listening tests on audio quality were naturally double blind.

In terms of the TetraMic, our experience was that in general the output from this mic was a much lower level signal, compared to say the Ambeo. So, my original point was not really that the Tetra is noiser, just that it requires more input gain compared to some other mics, which places more demands on whatever mic preamps are being used. And yes, I'm just referring to program level overall noise.

In our test, the mic preamps were quite modest (the MOTU 8m) although still fairly representative of the types of mic pres often used with these types of mics, hence the issue. So, as John also mentioned, when using the TetraMic with modest mic pres (such as a Motu, or a Zoom portable recorder), noise can be more of an issue with this mic compared to some others, but using better mic pres (such as the Metric Halo) much less so. To me this is something important to be aware of.

Steven, although it arrived too late to include in our tests, to my ears, the new Ambeo plugin greatly improves the high frequency response, so I'd definitely recommend trying it out.

Thanks for the offer Gerard, I'll let you know if we do ever plan on doing more tests like this.
enda

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[David Pickett]

Post by Enda Bates
In our test, the mic preamps were quite modest (the MOTU 8m) although
still fairly representative of the types of mic pres often used with
these types of mics, hence the issue. So, as John also mentioned, when
using the TetraMic with modest mic pres (such as a Motu, or a Zoom
portable recorder), noise can be more of an issue with this mic
compared to some others, but using better mic pres (such as the Metric
Halo) much less so. To me this is something important to be aware of.

There is something not quite right here. It seems quite crazy to
have to spend over USD 3000 for a preamp/AD convertor to use with a
microphone (Tetramic) which is designed to sell for USD 1300 (i.e.
much cheaper than the Soundfield). But I am not convinced that such
an expensive preamp is required. The Tetramic website says: "We've
found that a few commercial mic pre/ADCs will do the job. They are
the <http://www.motu.com/products/motuaudio/traveler-mk3/>MOTU
Traveler, <http://www.motu.com/products/motuaudio/4pre>MOTU 4Pre,
Metric Halo's <http://www.mhsecure.com/v5mm/ULN-8.html>ULN-8, Prism
Sound's
<http://www.prismsound.com/music_recording/products_subs/orpheus/orpheus_home.php>Orpheus,
Apogee's <http://www.apogeedigital.com/products/quartet>Quartet and
<http://www.rme-audio.de/en_products_fireface_ufx.php>RME Fireface UFX."

I am not a MOTU user, but at USD 449, the MOTU 4Pre presumably has a
quite adequate noise specification, or the highly competent Tetramic
engineers would not have mentioned it in the same sentence as the
more expensive options.

David

[Sampo Syreeni]

Post by David Pickett
I am not a MOTU user, but at USD 449, the MOTU 4Pre presumably has a
quite adequate noise specification, or the highly competent Tetramic
engineers would not have mentioned it in the same sentence as the more
expensive options.

Furthermore, on the digital side of things, we can buy somethhing
equivalent to yesterday's supercomputer for nickel and dime (cf.
Raspberry PI and its ilk). It doesn't seem quite right that we couldn't
engineer high quality analogue preamp circuitry towards a similarly low
price point, especially since the advances in digital circuitry are
synergistic with analogue designs.

It's been something like a decade since I looked into something like
Cirrus Logic or Analog Devices A/D silicon. Then a perfectly good four
channel, 16-18 bit equivalent chip cost somewhere in the vicinity of
$35. A reference PCB layout for it came free as well. Thus, the idea
that you'd now have to expend anything beyond some 100€'s in hardware in
order to get a fully functional, top of the line preamp for your top of
the line ambisonic mic, seems pretty much preposterous.

[John Leonard]

Well, of course, the ULN-8 isn’t just a pre-amp: it happens to have eight very nice low-noise high-gain mic pre-amps as part of the package, that’s all. Also, rather obviously, I didn’t buy the Tetramic and then the ULN-8. The ULN-8 has been at the centre of my studio set-up for many years and has proved to be well worth the money.

Empirically, based on my own experiences, the two low-cost (sub-$1,000.00) multitrack portable recorders that I tried after initially purchasing the Tetramic, were noisy at high gain when attempting to record quieter sounds with the Tetramic. I found that this was not the case with the ULN-8 and also with the Sound Devices 788T. We shall see how the SD Mix-Pre 6 behaves when it eventually reaches these shores.

As always, other people may have different experiences, but their needs may not be the same as mine.

Regards,

John

[Sampo Syreeni]

Post by John Leonard
Well, of course, the ULN-8 isn’t just a pre-amp: it happens to have
eight very nice low-noise high-gain mic pre-amps as part of the
package, that’s all.

Nowadays even the highest of the highest spheres in operational
amplifier technology costs something like 40 bucks per stereo pair. So,
with the minimum of high grade passive components included, and adding a
competitive markup, plus upholstery, it's unlikely you should have to
pay much in excess of 150 euros for your mic preamp. At that price
point, it already ought to look good as well as sounding nice.

What I mean to say here is that far too many people price themselves out
of the game. Analogue preamp engineering is not exactly the kind of
rocket surgery which calls for thousands of bucks at a pop. Done right,
using current top of the line components, it certainly makes its demands
known to your wallet. But when done right, it won't blow the bank.

Compared to the much more stringent and esoteric demands placed on a
well-designed spatial pickup feeding your preamp, the latter ought to be
a mere financial byline.

Post by John Leonard
Empirically, based on my own experiences, the two low-cost
(sub-$1,000.00) multitrack portable recorders that I tried after
initially purchasing the Tetramic, were noisy at high gain when
attempting to record quieter sounds with the Tetramic.

Then, regurgitating Fons's words, something is very wrong there. Using
current chips and just a hint of age old analog engineering knowhow e.g.
in how to make up a proper gain structure, you can *easily* get into
stable 18 bit territory for less than a hundred bucks, per four
channels. Getting past 20, predictably, start to run into diminishing
returns, true. But then pretty much nobody both has the mic to exercise
such extreme sensitivity, *while* at the same time running such a
forbidding absolute amplitude reference as to not be able to gain ride
any residual noise below the audibility threshold. Pretty much the only
folks with such stringent demands come from a film sound background,
with enough bucks from the get go to render the whole point moot.

Post by John Leonard
I found that this was not the case with the ULN-8 and also with the
Sound Devices 788T. We shall see how the SD Mix-Pre 6 behaves when it
eventually reaches these shores.

To reiterate, if you can hear any difference between such already rather
high end devices, somebody, somewhere royally fucked up. Even if my
understanding of analogue engineering is rather limited, still, given
the almost unreal performance of today's opamps as a building block,
even I am fully confident I could design a minimalistic, well-performing
mic preamp from scratch.

Post by John Leonard
As always, other people may have different experiences, but their
needs may not be the same as mine.

Granted, that. However, I'd still like to challenge you, as a
practitioner, a wee bit. What *are* your needs, really? How do you
quantify them, precisely?

I mean, once we know what you and the other practitioners are *really*
after, I'd contend that even a half-baked theoretician such as myself
could readily give rise to some rather magical sounding things. The kind
of bang for buck which is entirely two or three decades beyond what an
audiophile purveyor would have you believe is possible.

[David Pickett]

This whole business of low noise microphones and preamps is in my
experience a non-issue in the vast majority of cases. Very few
environments are quiet enough to be softer than the noise level of
most microphones. This is true in most cases of recording nature
sounds and very few recording studios get down below NC 20. Concert
halls are even noisier, and we rarely make recordings in anechoic
chambers, however isolated they may be.

Sampo is right about the ease with which a high quality mic amp can
be put together, taking reasonable (and obvious) precaution with
screening, rf suppression and PSU smoothing. I made a simple
two-channel amp with two THAT1510 ICs in a small box for use with
ribbon microphones. It can be powered for hours from two PP3
batteries, and measures and sounds as well as my much more expensive
RME UFX amplifiers.

David

[David Pickett]

Post by David Pickett
This whole business of low noise microphones and preamps is in my
experience a non-issue in the vast majority of cases.

That said, I was upset to discover that MOTU publish no details on
their website of the 4Pre that can be construed as truly technical.

A Sound on Sound review of the larger box says:

"MOTU don't publish any specifications for the 8Pre's analogue
circuitry, such as frequency response or signal-to-noise ratio. While
it might be nice to know these things, it could be argued that exact
figures are almost meaningless to the typical user the 8Pre is aimed
at. In any case, modern digital electronics design almost always
ensures that signal-to-noise ratio and bandwidth are no longer the
key concerns for the performance of an audio interface."

...

David

[Sampo Syreeni]

Post by David Pickett
This whole business of low noise microphones and preamps is in my
experience a non-issue in the vast majority of cases.

That said, I was upset to discover that MOTU publish no details on their
website of the 4Pre that can be construed as truly technical. [...]

Obviously they should publish their figures. In fact I don't think we
should really implicitly trust any figure given out by any equipment
purveyor. Instead we should, how was it now, "trust, but verify".

My personal waking up experience there was when I as a teenager upgraded
from a Gravis Ultrasound soundcard to a Gravis Ultrasound MAX. At the
time those were the most cost efficient means of producing sampled sound
from a PC expansion card, and I believe it's settled the original Gravis
card, at least in its later iterations, can still be called a small
marvel of sound, low-cost engineering.

The MAX on the other hand immediately sounded noisy and irritating to
me. Of course I still just had to have it, because it was the first
credible consumer range card on the market to not only support 44/16
playback, but to have it done at low central processor load. Gravis
achieved that by tacking on a separate Crystal Logic two channel
converter chip (CS4231), while leaving their existing custom GF1 ASIC
chip to do offloaded sample playback synthesis (32 voices!!!). The
efficiency gain in direct playback was because you could do DMA over the
ISA bus, without the tortuous peeking and poking and unreliable
DMA-to-device-memory, and chunking to fit register constraints, and
without any hardware synchronization on board the GF1, and whatnot.
Programming that chip was sheer hell, which showed in any application
not doing precisely what it was meant to do, and everybody liked the
stupider, more direct access of the MAX's new chip.

Except that the card sounded like shit. No user accessible feature of it
made it silent. It not only hissed, it let through power supply
fluctuations. Those emanating from hard drive seek servoes, in
particular.

I eventually got incensed enough to actually contact Crystal Logic, and
procure the new chip's databook. (Then they still used to send them for
free, over mail.) My first analysis of the problem was that they had
this new, unknown to me thingy called "dither" in there, and after duly
disassembling half of Gravis's driver code, I determined it was turned
on. So I dialed, a number of times over successive days or perhaps even
weeks, Gravis's Finnish helpline. (They had to have that, because the
Finnish Demo Scene was a considerable driver of Gravis sales then. Demos
can't waste any cycle, now..? ;) ) I pestered the hell out of a couple
of service reps and even a couple of engineers, to no eventual avail. I
resigned to the reality of a now-shitty soundcard, and eventually just
switched it out as part of technological development.

A few years later, after I'd finally taken a slightly more involved look
into mixed analogue-digital engineering as well -- and still nothing
spectacular, just the barest of basics -- I suddenly thought to look
back at my noise problem with the MAX. As it happened, I still had the
databook of the new converter chip with me, with its reference PCB
design, not to mention both the physical card *and* a '486 carrying
motherboard in which to plug it.

If I remember correctly, I ended up cutting a couple of line level
connects on the board and rerouting them through a haphazard out of
board capacitive traps. Did something similar to separate a couple of
digital signals, including the the clock signal to the new converter
chip, from the analogue earth. Put a bit of actual tin foil encased
in saran wrap over the digital section, strategically grounded.

...and then most crucially completely reworked how the analogue
reference of the new converter chip was fed. Because that was the true
root cause of the problem: for some reason unfathomable to me, Gravis's
engineers had decided to mostly adapt Cirrus's reference layout for the
new section, *except* for the *explicit* warnings against in *any* way
directly coupling the pin to the workings of the digital section. Even
touching its (in itself well designed, wide) ground willy-nilly, because
of what ground resistance and reactance do to all of them funny-funny
digital switching transients (remember, at that time the voltages and
currents we worked with on the digital side were at least a decade and
sometimes more beyond today's figures). The circuit board also relied on
external regulation alone, with typically *very* substandard performance
as far as audiophiles would have it; while the first iteration with only
the GF1 ASIC and its analogue output circuitry had been well designed to
withstand that, the added-on Cirrus chip couldn't cope with that at all.

The final version of my modifications brought down the total noise
somewhere in excess of 30dB. The end result just fell silent, as it
should have been from the start. I'm also rather certain the same result
could have been achieved at negligible cost had the PCB been designed
right from the start; even going with Cirrus's reference design and the
ample commentary which came with it, the board could have been as first
rate as the first iteration was. Combining those two separate teams'
efforts fully, I'm pretty sure they could have exceeded my eventual
achieved performance by at least a couple of decibels in inherent noise
and power supply rejection -- my modifications having costed something
in the vicinity of 15€ in current money, while being total overkill, and
achievable by sane, careful circuit design at a tenth or even a hundreth
of the total cost.

Long story short, openness and the sane engineering discipline which
goes along with it can achieve a lot. Even in the lowest realms of
engineering. In this case, with one half-clueless teenager rectifying an
ex post *obvious* engineering fault of a well-performing, already mostly
well-engineered mass-market product.

[Sampo Syreeni]

Post by David Pickett
This whole business of low noise microphones and preamps is in my
experience a non-issue in the vast majority of cases. Very few
environments are quiet enough to be softer than the noise level of
most microphones.

Agreed, and thanks for pointing that aspect out aloud. Quite a number of
people -- myself in particular because I have very little on-field
experience -- tend to be swayed by minute theoretical disagreements
which have absolutely nothing to do with our two shared goals: the best
all-round practical signal chain possible, and the best sounding records
(in their many forms) achievable within its bounds.

Post by David Pickett
Sampo is right about the ease with which a high quality mic amp can be
put together, taking reasonable (and obvious) precaution with
screening, rf suppression and PSU smoothing. [...]

Now if only all of the bucks being thrown at the problem went to
mitigating such real and well known culprits. If only we did high
fidelity and the high tech which goes along with it at the *true*
fidelity margin, at all price points. I mean if we ever got close to
something like *that* principle, you could even today have a well
rounded, effective setup for less than a week's pay. If you decided to
invest more and had the wherewithal to go there, you could do even
better -- but now all-round, so that what you saved in your mic and
preamp, you could invest into acoustic treatment, professional help and
whatnot, which currently tend to be underappreciated wrt to the
difference they make.

I have a dream... :D

[Eero Aro]

Post by Sampo Syreeni

Post by David Pickett
This whole business of low noise microphones and preamps is in my
experience a non-issue in the vast majority of cases. Very few
environments are quiet enough to be softer than the noise level of
most microphones.

Agreed, and thanks for pointing that aspect out aloud. Quite a number of
people -- myself in particular because I have very little on-field
experience -- tend to be swayed by minute theoretical disagreements
which have absolutely nothing to do with our two shared goals: the best
all-round practical signal chain possible, and the best sounding records
(in their many forms) achievable within its bounds.

I agree that in most cases the noise isn't a critical factor in recording.

However, here is an example of minority:

I recorded radio plays (monirty) in the Finnish language (minority) in
Finland
(minority). The Finnish population is just five million and about 10% of
the population
don't speak Finnish as their mother language. Some radio plays get just
20.000
listeners. (Though some plays I produced, got half a million. :-) )

Still, I tried to use Ambisonics in radio production for a period of
time in the 1990's.
At the best time I knew nine listeners, who had a decoder and a speaker
setup.
Minority! I could have phoned them all and informed about the next UHJ
transmission,
no need to put the information in the newspaper.

Anyway, the microphone wasn't the biggest problem in the production,
there were
many other other things, but very soon I noticed that I couldn't use the
Soundfield
microphones at all. Their self noise was too high. I was using the MK
IV, ST250
and the MK V.

It was much better to use single low noise mono microphones, such as the
Sennheiser MKH 30 and to place the signal into the soundfield by panning.
I often used stereo pairs to capture also the actors movements.

The Finnish Radio Drama is similar to other Scandinavian countries in
that actors
use a large variation in their speech. Sometimes they go very soft, less
than
whispering. This is not very common in Radio Drama in many parts of the
world.
Very often the actors just "read" loud.

However, using a Soundfield in a radio drama studio isn't very clever,
as there isn't
any special acoustics that would need to be recorded. It is much easier
to add
the room acoustics with a signal processor. I used a four channel output
Lexicon
and the Quantec Room Simulator.

Using the Soundfield in on-location recordings would have captured nice
acoustics,
but the Soundfields of that time were very clumsy to use in the field.
You couldn't
move with a Soundfield and follow the actors, as the suspension was
lousy and
caused noises and the windshields grew very large.

As a compromise, I recorded atmospheres on location without the actors
and mixed those into the play and that lead into good results. But took much
more time, which always wasn't available in radio production.

Eero

[John Leonard]

http://www.johnleonard.co.uk

I look forward to seeing you enter into the market.

Regards,

John

Please note new email address & direct line phone number
email: ***@johnleonard.uk
phone [phone]

Granted, that. However, I'd still like to challenge you, as a practitioner, a wee bit. What *are* your needs, really? How do you quantify them, precisely?

[Augustine Leudar]

Interesting work you are doing. Any thoughts on the Nagra vs the Sound
devices recorders ? also do you have any stereo or mono mic recommendations
for natural field recordings ?

Post by John Leonard
Well, of course, the ULN-8 isn’t just a pre-amp: it happens to have eight
very nice low-noise high-gain mic pre-amps as part of the package, that’s
all. Also, rather obviously, I didn’t buy the Tetramic and then the ULN-8.
The ULN-8 has been at the centre of my studio set-up for many years and has
proved to be well worth the money.
Empirically, based on my own experiences, the two low-cost (sub-$1,000.00)
multitrack portable recorders that I tried after initially purchasing the
Tetramic, were noisy at high gain when attempting to record quieter sounds
with the Tetramic. I found that this was not the case with the ULN-8 and
also with the Sound Devices 788T. We shall see how the SD Mix-Pre 6 behaves
when it eventually reaches these shores.
As always, other people may have different experiences, but their needs
may not be the same as mine.
Regards,
John
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[Steven Boardman]

There is something not quite right here. It seems quite crazy to have to spend over USD 3000 for a preamp/AD convertor to use with a microphone (Tetramic) which is designed to sell for USD 1300 (i.e. much cheaper than the Soundfield). But I am not convinced that such an expensive preamp is required. The Tetramic website says: "We've found that a few commercial mic pre/ADCs will do the job. They are the <http://www.motu.com/products/motuaudio/traveler-mk3/ <http://www.motu.com/products/motuaudio/traveler-mk3/>>MOTU Traveler, <http://www.motu.com/products/motuaudio/4pre <http://www.motu.com/products/motuaudio/4pre>>MOTU 4Pre, Metric Halo's <http://www.mhsecure.com/v5mm/ULN-8.html <http://www.mhsecure.com/v5mm/ULN-8.html>>ULN-8, Prism Sound's <http://www.prismsound.com/music_recording/products_subs/orpheus/orpheus_home.php <http://www.prismsound.com/music_recording/products_subs/orpheus/orpheus_home.php>>Orpheus, Apogee's <http://www.apogeedigital.com/products/quartet <http://www.apogeedigital.com/products/quartet>>Quartet and <http://www.rme-audio.de/en_products_fireface_ufx.php <http://www.rme-audio.de/en_products_fireface_ufx.php>>RME Fireface UFX."
I am not a MOTU user, but at USD 449, the MOTU 4Pre presumably has a quite adequate noise specification, or the highly competent Tetramic engineers would not have mentioned it in the same sentence as the more expensive options.
David

Hi David,

I use the Motu 4pre (with a tablet for on the fly decodes), with a Zoom F8 in the field. I also have a RME Fireface in the studio.
None have problems with the noise floor being louder than that of the mic.
The noise of the Tetramic is only a problem when the subject is quiet or far away. So for most musical applications it’s great. If you are trying to capture wildlife at a distance then there are better options…

Best

Steve
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[David Pickett]

Post by Steven Boardman
I use the Motu 4pre (with a tablet for on the fly decodes), with a
Zoom F8 in the field. I also have a RME Fireface in the studio.
None have problems with the noise floor being louder than that of the mic.
The noise of the Tetramic is only a problem when the subject is quiet
or far away. So for most musical applications it’s great. If you are
trying to capture wildlife at a distance then there are better options…

Quite so. As I read the article, I didnt have the
impression that the sources used were all that
challenging in terms of loudness. The noise and
sensitivity spec on the Tetramic is quite satisfactory:

"... Self noise: 19 dBA per capsule. Self noise
can decrease or increase depending on selected decode

"Maximum SPL per capsule: 135 dB Sensitivity per
capsule: 7.0 mV/Pa nominal (-43 dB ref: 1V/Pa) ..."

I cannot find comparably detailed specifications
for the MOTU 4Pre, but the sensitivity demands above are not extreme.

Post by Steven Boardman
It's been something like a decade since I looked
into something like Cirrus Logic or Analog
Devices A/D silicon. Then a perfectly good four
channel, 16-18 bit equivalent chip cost
somewhere in the vicinity of $35. A reference
PCB layout for it came free as well. Thus, the
idea that you'd now have to expend anything
beyond some 100€'s in hardware in order to get a
fully functional, top of the line preamp for
your top of the line ambisonic mic, seems pretty much preposterous.

Indeed so. I cant quote prices for the A/D
stage, but the one-off price of a THAT1512 analog
input amplifier costs only EUR 6.82 at
Mouser.com, and requires only a few additional components.

David

[Augustine Leudar]

I use Zoom H2 and H2N and Motu interfaces (ultralite and 24 ao with
ada8200) the pres are fine - the line/mic in on a zoom h2n ,a little
minijack input, are quite noisy however - so I usually prefer to use the
onboard mics than an external with this device.

Post by Steven Boardman
I use the Motu 4pre (with a tablet for on the fly decodes), with a
Zoom F8 in the field. I also have a RME Fireface in the studio.
None have problems with the noise floor being louder than that of the mic.
The noise of the Tetramic is only a problem when the subject is quiet
or far away. So for most musical applications it’s great. If you are
trying to capture wildlife at a distance then there are better options…

Quite so. As I read the article, I didnt have the impression that the
sources used were all that challenging in terms of loudness. The noise and
"... Self noise: 19 dBA per capsule. Self noise can decrease or increase
depending on selected decode
"Maximum SPL per capsule: 135 dB Sensitivity per capsule: 7.0 mV/Pa
nominal (-43 dB ref: 1V/Pa) ..."
I cannot find comparably detailed specifications for the MOTU 4Pre, but
the sensitivity demands above are not extreme.
It's been something like a decade since I looked into something like

Post by Steven Boardman
Cirrus Logic or Analog Devices A/D silicon. Then a perfectly good four
channel, 16-18 bit equivalent chip cost somewhere in the vicinity of $35. A
reference PCB layout for it came free as well. Thus, the idea that you'd
now have to expend anything beyond some 100€'s in hardware in order to get
a fully functional, top of the line preamp for your top of the line
ambisonic mic, seems pretty much preposterous.

Indeed so. I cant quote prices for the A/D stage, but the one-off price
of a THAT1512 analog input amplifier costs only EUR 6.82 at Mouser.com, and
requires only a few additional components.
David
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[Fons Adriaensen]

Post by David Pickett
the <http://www.motu.com/products/motuaudio/traveler-mk3/>MOTU
Traveler, <http://www.motu.com/products/motuaudio/4pre>MOTU 4Pre,
Metric Halo's <http://www.mhsecure.com/v5mm/ULN-8.html>ULN-8, Prism
Sound's <http://www.prismsound.com/music_recording/products_subs/orpheus/orpheus_home.php>Orpheus,
Apogee's <http://www.apogeedigital.com/products/quartet>Quartet and
<http://www.rme-audio.de/en_products_fireface_ufx.php>RME Fireface UFX."
I am not a MOTU user, but at USD 449, the MOTU 4Pre presumably has a
quite adequate noise specification, or the highly competent Tetramic
engineers would not have mentioned it in the same sentence as the
more expensive options.

MOTU doesn't provide an EIN figure for any of the products listed
above. The price doesn't tell you anything either.

All the others do, and they are all in the -127 to -130 dBu range,
so at least 11 dB below the Tetramic's own noise level. That means
they'll add less than 0.5 dB.

Ciao,