"xy" wrote in message
om...
http://www.rollmusic.com/systems/folcrom.shtml

I'm not smart enough with electronics to understand if it's a good
ciruit idea or not. It seems cool. But what do I know!

I was hoping some of the circuit-gods around here could offer any
thoughts on it.

Well as described it should work

For example, I'm wondering how something completely passive like that
can maintain proper gain staging,

Well it doesnt. let me quote "requires approximately 30-40dB of make-up
gain" in other words because it is a passive mixer it effectively adds up to
30-40dB of loss meaning it needs to be followed by a pre-amp

and how it could stay quiet and

No active components = bugger all noise

reject rf.

It is shielded


But again, I'm bad at electronics!

On the other hand I just looked at the Price $1000 USD !!!!!!! It would be
expensive at 1/4 that price !

Regards
Richard Freeman

Arjan P wrote in message ...
What a joke.

Actually, it's not a joke.

Electronically it makes sense, with one exception, which I'll get to in a
moment. But unless they're using very high-quality switches for 20 years of
reliability, it's way the hell overpriced. A prosumer version of this could
go for perhaps $250, a higher-quality one (again, that mostly means better
switches) for $450-500.

Like I said, electronically it makes sense; the gain staging should work
okay. If the nominal output level is -35dBu, and the nominal output
impedance is 150 ohms, that'll work just fine with a typical microphone
preamp. If the latter has an input equivalent noise level of -127dBu, then
you'll get a signal-to-noise ratio of 92dB, relative to nominal level, and
however much headroom your converters allow.

The fly in the ointment is the crosstalk spec and the switching. They say
it's -90 dB, but they don't say how that number's derived. My guess is that
it's the figure for how much leaks into the left channel when you're driving
the right channel, or vice versa. All very well and good, if that's all
that's punched in.

But they also give you the facility to swtich an input to both channels at
once, and that will degrade the separation some. I calculate that pushing in
one pair of buttons to switch that channel to the center makes the
separation more like -76 dB, and pushing in more pairs degrades it further.
Maybe the distinction's academic, but it should be noted.

You could build a switchbox like this yourself, and if you remember to only
switch inputs to left or right, not both, getting center stuff by panning,
you could get very nice results, and use up a wad of solder. Of course, then
your results will depend on the quality of your D/A converters.

Peace,
Paul

Since I designed the Folcrom and I'm selling it, I don't expect anybody
to take my word for it that it's a good idea. The people who have been
buying it seem to think it's a good idea, as we've gotten a
surprisingly strong and positive response so far. I'll comment on some
of the commentary below.

Paul Stamler wrote:

Electronically it makes sense, with one exception, which I'll get to in a
moment. But unless they're using very high-quality switches for 20 years of
reliability, it's way the hell overpriced. A prosumer version of this could
go for perhaps $250, a higher-quality one (again, that mostly means better
switches) for $450-500.

I've had to defend the price of the Folcrom on several occasions when
DIY types suggest it's nothing more than a box of resistors and that it
should cost some ridiculously paltry amount. I could have thrown in
three dollars' worth of op-amps and a wall wart and it wouldn't be
passive, and nobody would complain about the price. The fact is that
the bulk of the parts cost lies in the chassis, the switches, and the
circuitboards. The difference between a passive circuit and an active
one does not amount to a meaningful percentage of the selling price.
The parts cost only accounts for about a quarter of the selling price,
which is typical for any gear you buy. Aside from parts cost, there's
also dealer mark-up, distribution costs, assembly labor, and facility
overhead to account for the majority of the cost. I'm not quite
getting rich off this thing. The dealers I'm working with and my
partners seem to think the price is a bit too low, and in fact I think
it's right about where it should be. In truth a person who's handy
with a soldering iron and friendly with a metal shop could build one
for about $300 if they soldered everything point-to-point, but that
would take a hell of a long time. The circuitboard design would be a
hurdle for most DIY folks, which makes the selling price of my box seem
pretty reasonable. Is it worth 30 hours of your time to save $400?
The Folcrom is sturdy and well-built, it looks good, and comes with a
warranty.

Like I said, electronically it makes sense; the gain staging should work
okay. If the nominal output level is -35dBu, and the nominal output
impedance is 150 ohms, that'll work just fine with a typical microphone
preamp. If the latter has an input equivalent noise level of -127dBu, then
you'll get a signal-to-noise ratio of 92dB, relative to nominal level, and
however much headroom your converters allow.

Exactly. Many folks don't immediately realize that any normal, active
mixer has a make-up gain amplifier built into it. The noise
performance of the Folcrom coupled with a good low-noise preamp is no
worse than a good quiet mixer with built-in makeup gain. In fact it is
even quieter because we left out all kinds of circuitry that's needed
in a traditional mixer but unnecessary in a DAW-summing application.

The fly in the ointment is the crosstalk spec and the switching. They say
it's -90 dB, but they don't say how that number's derived. My guess is that
it's the figure for how much leaks into the left channel when you're driving
the right channel, or vice versa. All very well and good, if that's all
that's punched in.

But they also give you the facility to swtich an input to both channels at
once, and that will degrade the separation some. I calculate that pushing in
one pair of buttons to switch that channel to the center makes the
separation more like -76 dB, and pushing in more pairs degrades it further.
Maybe the distinction's academic, but it should be noted.

It's actually very difficult to pin down an accurate, meaningful
specification for either crosstalk or noise. The measurements will
always depend on what's feeding the Folcrom and what the Folcrom is
feeding. The crosstalk specification we give (-90dB) is sort of a
best-case scenario for the real world. Paul's right that assigning
numerous channels to mono (both left and right output) will degrade the
crosstalk performance somewhat, but that degradation will be very
slight when the Folcrom is fed by a high quality source. In this
context I'm defining "high quality" as a very low-impedance source. A
theoretically ideal source, having zero impedance, would not degrade
the crosstalk whatsoever. Any high quality DAC ought to have a source
impedance of under 100 ohms, which will have a negligible impact on the
crosstalk even if several channels are bussed mono. I would put the
worst-case scenario, barring any unusually high-impedance sources, at
about -70dB.

Let's also remember that this is a mixer we're talking about. Its
output is a stereo mix that you're going to listen to on a pair of
speakers. Crosstalk between the left and right channels is about the
most unimportant specification I can think of. What's the separation
of an LP being played by a good cartridge through a pair of speakers
placed 10 feet apart? In reality, the potential "degradation" of the
crosstalk Paul describes will be absolutely undetectable to even the
most critical listener.

You could build a switchbox like this yourself, and if you remember to only
switch inputs to left or right, not both, getting center stuff by panning,
you could get very nice results, and use up a wad of solder. Of course, then
your results will depend on the quality of your D/A converters.

You absolutely could build a box like this yourself for less than half
of what you can buy mine for. But it'll be a lot of work. And if you
leave out the switches so that you can't assign an input to more than
one channel, nor mute an unused channel, then you'll shave the cost of
the actual mixer substantially. But then you'll need twice as many DAC
channels to feed your mono signals, and you'll have to build dummy
plugs to short any input that's not in use. Those items will cost
substantially more than the price difference between a stripped-down
DIY version and the store-bought version.

In summary, the Folcrom is actually a pretty good idea. We spent a
long time developing and refining the design, and in practice the
device works very well. Users have been thrilled with the ability to
change the sound of their mix buss by switching make-up gain
amplifiers. Its price reflects its production costs and is on the low
side of industry norms.

Justin, I agree with almost everything you say. (Although, I believe
a point-to-point version will actually improve it a little further).

I don't think you are charging too much at all. In fact, your basic
concept already exists, but in a more pricey form: The Millennia
Media Mixing Suite. If you were to price out the equivalent in
the 'Suite with passive channels installed (there are actually two
levels of "passivity"), it would end up being a fair bit more than
the Folcrom. However, then you would have the gain section built in
with various other master section features such as headphone outputs,
oscillator etc. The Suite would be about $3 to 4 thousand in the
equivalent form. It is probably a little higher in quality, but
still at $1000, I think you have a very nice price.

Rob R.

Justin Ulysses Morse wrote:
Since I designed the Folcrom and I'm selling it, I don't expect anybody
to take my word for it that it's a good idea. The people who have been
buying it seem to think it's a good idea, as we've gotten a
surprisingly strong and positive response so far. I'll comment on some
of the commentary below.

Paul Stamler wrote:

Electronically it makes sense, with one exception, which I'll get to in a
moment. But unless they're using very high-quality switches for 20 years of
reliability, it's way the hell overpriced. A prosumer version of this could
go for perhaps $250, a higher-quality one (again, that mostly means better
switches) for $450-500.

I've had to defend the price of the Folcrom on several occasions when
DIY types suggest it's nothing more than a box of resistors and that it
should cost some ridiculously paltry amount. I could have thrown in
three dollars' worth of op-amps and a wall wart and it wouldn't be
passive, and nobody would complain about the price. The fact is that
the bulk of the parts cost lies in the chassis, the switches, and the
circuitboards. The difference between a passive circuit and an active
one does not amount to a meaningful percentage of the selling price.
The parts cost only accounts for about a quarter of the selling price,
which is typical for any gear you buy. Aside from parts cost, there's
also dealer mark-up, distribution costs, assembly labor, and facility
overhead to account for the majority of the cost. I'm not quite
getting rich off this thing. The dealers I'm working with and my
partners seem to think the price is a bit too low, and in fact I think
it's right about where it should be. In truth a person who's handy
with a soldering iron and friendly with a metal shop could build one
for about $300 if they soldered everything point-to-point, but that
would take a hell of a long time. The circuitboard design would be a
hurdle for most DIY folks, which makes the selling price of my box seem
pretty reasonable. Is it worth 30 hours of your time to save $400?
The Folcrom is sturdy and well-built, it looks good, and comes with a
warranty.

Like I said, electronically it makes sense; the gain staging should work
okay. If the nominal output level is -35dBu, and the nominal output
impedance is 150 ohms, that'll work just fine with a typical microphone
preamp. If the latter has an input equivalent noise level of -127dBu, then
you'll get a signal-to-noise ratio of 92dB, relative to nominal level, and
however much headroom your converters allow.

Exactly. Many folks don't immediately realize that any normal, active
mixer has a make-up gain amplifier built into it. The noise
performance of the Folcrom coupled with a good low-noise preamp is no
worse than a good quiet mixer with built-in makeup gain. In fact it is
even quieter because we left out all kinds of circuitry that's needed
in a traditional mixer but unnecessary in a DAW-summing application.

The fly in the ointment is the crosstalk spec and the switching. They say
it's -90 dB, but they don't say how that number's derived. My guess is that
it's the figure for how much leaks into the left channel when you're driving
the right channel, or vice versa. All very well and good, if that's all
that's punched in.

But they also give you the facility to swtich an input to both channels at
once, and that will degrade the separation some. I calculate that pushing in
one pair of buttons to switch that channel to the center makes the
separation more like -76 dB, and pushing in more pairs degrades it further.
Maybe the distinction's academic, but it should be noted.

It's actually very difficult to pin down an accurate, meaningful
specification for either crosstalk or noise. The measurements will
always depend on what's feeding the Folcrom and what the Folcrom is
feeding. The crosstalk specification we give (-90dB) is sort of a
best-case scenario for the real world. Paul's right that assigning
numerous channels to mono (both left and right output) will degrade the
crosstalk performance somewhat, but that degradation will be very
slight when the Folcrom is fed by a high quality source. In this
context I'm defining "high quality" as a very low-impedance source. A
theoretically ideal source, having zero impedance, would not degrade
the crosstalk whatsoever. Any high quality DAC ought to have a source
impedance of under 100 ohms, which will have a negligible impact on the
crosstalk even if several channels are bussed mono. I would put the
worst-case scenario, barring any unusually high-impedance sources, at
about -70dB.

Let's also remember that this is a mixer we're talking about. Its
output is a stereo mix that you're going to listen to on a pair of
speakers. Crosstalk between the left and right channels is about the
most unimportant specification I can think of. What's the separation
of an LP being played by a good cartridge through a pair of speakers
placed 10 feet apart? In reality, the potential "degradation" of the
crosstalk Paul describes will be absolutely undetectable to even the
most critical listener.

You could build a switchbox like this yourself, and if you remember to only
switch inputs to left or right, not both, getting center stuff by panning,
you could get very nice results, and use up a wad of solder. Of course, then
your results will depend on the quality of your D/A converters.

You absolutely could build a box like this yourself for less than half
of what you can buy mine for. But it'll be a lot of work. And if you
leave out the switches so that you can't assign an input to more than
one channel, nor mute an unused channel, then you'll shave the cost of
the actual mixer substantially. But then you'll need twice as many DAC
channels to feed your mono signals, and you'll have to build dummy
plugs to short any input that's not in use. Those items will cost
substantially more than the price difference between a stripped-down
DIY version and the store-bought version.

In summary, the Folcrom is actually a pretty good idea. We spent a
long time developing and refining the design, and in practice the
device works very well. Users have been thrilled with the ability to
change the sound of their mix buss by switching make-up gain
amplifiers. Its price reflects its production costs and is on the low
side of industry norms.

Justin Ulysses Morse wrote:

Since I designed the Folcrom and I'm selling it, I don't expect anybody
to take my word for it that it's a good idea. The people who have been
buying it seem to think it's a good idea, as we've gotten a
surprisingly strong and positive response so far. I'll comment on some
of the commentary below.

So what's the maximum input level? 42 dB-what?

S O'Neill wrote:

So what's the maximum input level? 42 dB-what?

It's pretty arbitrary, really. There's nothing in the Folcrom that can
be overloaded, but if you put enough signal in then eventually the 1/4W
resistors will overheat. I calculated that to be an input signal of
100.75 volts RMS on any single input channel. I believe that's
42.28dBv.

However, if all 16 inputs were driven with equal and fully-correlated
(identical) signals and all fed to the same (left or right) output
buss, then the maximum level for each channel would be 76.49VRMS before
the summing (output) resistors would overheat. I think that's
+39.89dBv. Obviously none of things are ever going to happen in the
real world, so there's not really a need for a MOL specification other
than an academic one.


Rob Reedijk wrote:

It is probably a little higher in quality, but still at $1000, I think you have a very nice price.

Thanks for the support. And actually, the street price of the Folcrom
is $795.

ulysses

What I don't understand about this type of box (both this one & the active
ones made by other companies) is how they can actually accomplish what the
claim to. I've read claims that they "avoid the resolution loss that
occurs when lowering gain digitally" (paraphrase). But if they don't
include pots or faders, you still have to controll the gain digitally. Is
there some "Magic" in running what for all practical purposes is a digital
mix through an analog summing bus? Or is it pretty much the same as mixing
down digital tracks to analog tape?

agent86 wrote:

What I don't understand about this type of box (both this one & the
active ones made by other companies) is how they can actually
accomplish what the claim to. I've read claims that they "avoid the
resolution loss that occurs when lowering gain digitally"
(paraphrase).

The basic claim that there is a resolution loss when gain is lowered
digitally ignores all of the DAW software that either does summing in 64 bit
fixed point, or 32 bit floating point. 64 bits gives something like 300 dB
dynamic range, and 32 bit floating point gives about 1,000 dB dynamic range.
Wither is obviously grotesque overkill, but they are the next logical step
up from the 140 or so dB of dynamic range you get with 24 bit fixed point,
minus the losses inherent in mixing.

Paul Stamler's post estimated a best case SNR of about 92 dB, which pales
compared to the 130 dB dynamic range in much of the DAW software that is
supposedly being improved upon.

But if they don't include pots or faders, you still
have to control the gain digitally. Is there some "Magic" in
running what for all practical purposes is a digital mix through an
analog summing bus?

The only magic I see is along the lines of "Look over there, cakes!"

Or is it pretty much the same as mixing down digital tracks to analog
tape?

If the discussion is about dynamic range, don't go anywhere near analog
tape!

Arny Krueger wrote:

agent86 wrote:

What I don't understand about this type of box (both this one & the
active ones made by other companies) is how they can actually
accomplish what the claim to. I've read claims that they "avoid the
resolution loss that occurs when lowering gain digitally"
(paraphrase).

The basic claim that there is a resolution loss when gain is lowered
digitally ignores all of the DAW software that either does summing in 64
bit
fixed point, or 32 bit floating point. 64 bits gives something like 300
dB dynamic range, and 32 bit floating point gives about 1,000 dB dynamic
range. Wither is obviously grotesque overkill, but they are the next
logical step up from the 140 or so dB of dynamic range you get with 24 bit
fixed point, minus the losses inherent in mixing.

Paul Stamler's post estimated a best case SNR of about 92 dB, which pales
compared to the 130 dB dynamic range in much of the DAW software that is
supposedly being improved upon.

But if they don't include pots or faders, you still
have to control the gain digitally. Is there some "Magic" in
running what for all practical purposes is a digital mix through an
analog summing bus?

The only magic I see is along the lines of "Look over there, cakes!"

Or is it pretty much the same as mixing down digital tracks to analog
tape?

If the discussion is about dynamic range, don't go anywhere near analog
tape!


I'm inclined to agree with you're point of view, Arny. But even if you buy
the argument about digital resolution vs decreasing gain, these boxes don't
even address that. All the gain adjustments STILL happen in the DAW. An
analog summing bus without faders or pot is NOT an analog mixer AFAIK.

If the argument were that the mathematical calculations within the digital
summing bus were themselves inherently flawed, I could buy that. (Or I
could at least consider it a point worthy of discussion.) But that would
also raise the question of why one would expect the mathematical
calculations within the DA & AD converters to be any less flawed. Then you
have to decide whether any potential benefit gained by summing in analog
exceded the potential loss associated with two extra generations of
conversion.

It's a damn wonder anybody finds time to actually record anything.

agent86 wrote:

If the argument were that the mathematical calculations within the digital
summing bus were themselves inherently flawed, I could buy that. (Or I
could at least consider it a point worthy of discussion.)

This is the argument for analog summing. We know that digital summing
should theoretically be perfect but so far all of the claims that
real-world software is in fact perfect seem to grossly underestimate
some software companies' ability to screw it up. That's my current
view of the situation, anyway. Unfortunately this is one of the most
difficult areas to perform conclusive, objective tests because there
are just so many variables.

But that would also raise the question of why one would expect the
mathematical calculations within the DA & AD converters to be any
less flawed.

The DACs themselves simply aren't asked to perform this particular kind
of calculation.

Then you have to decide whether any potential benefit
gained by summing in analog exceded the potential loss associated
with two extra generations of conversion.

And that's where the real meat lies. People who have tried analog
summing have overwhelmingly concluded that they like the effect it has
on the sound of their mixes and their approach to mixing. That's what
really matters to most engineers I know.

It's a damn wonder anybody finds time to actually record anything.

When's the last time I posted about a recording project of my own?

ulysses

agent86 wrote:
Arny Krueger wrote:

agent86 wrote:

What I don't understand about this type of box (both this one & the
active ones made by other companies) is how they can actually
accomplish what the claim to. I've read claims that they "avoid the
resolution loss that occurs when lowering gain digitally"
(paraphrase).

The basic claim that there is a resolution loss when gain is lowered
digitally ignores all of the DAW software that either does summing
in 64 bit
fixed point, or 32 bit floating point. 64 bits gives something like
300 dB dynamic range, and 32 bit floating point gives about 1,000 dB
dynamic range. Wither is obviously grotesque overkill, but they are
the next logical step up from the 140 or so dB of dynamic range you
get with 24 bit fixed point, minus the losses inherent in mixing.

Paul Stamler's post estimated a best case SNR of about 92 dB, which
pales compared to the 130 dB dynamic range in much of the DAW
software that is supposedly being improved upon.

But if they don't include pots or faders, you still
have to control the gain digitally. Is there some "Magic" in
running what for all practical purposes is a digital mix through an
analog summing bus?

The only magic I see is along the lines of "Look over there, cakes!"

Or is it pretty much the same as mixing down digital tracks to
analog tape?

If the discussion is about dynamic range, don't go anywhere near
analog tape!


I'm inclined to agree with you're point of view, Arny. But even if
you buy the argument about digital resolution vs decreasing gain,
these boxes don't even address that. All the gain adjustments STILL
happen in the DAW. An analog summing bus without faders or pot is
NOT an analog mixer AFAIK.

Agreed.

If the argument were that the mathematical calculations within the
digital summing bus were themselves inherently flawed, I could buy
that. (Or I could at least consider it a point worthy of discussion.)
But that would also raise the question of why one would expect the
mathematical calculations within the DA & AD converters to be any
less flawed.

Different products, different vendors, different development cycles,
hardware versus software.

But, none of these factors would apply to every implmentation, just some of
them.

Then you have to decide whether any potential benefit
gained by summing in analog exceded the potential loss associated
with two extra generations of conversion.

A digital mixer is a picture of simplicity compared to a converter. For
example a digital mixer need not have any brick wall filters or
frequency-dependent processing.

It's a damn wonder anybody finds time to actually record anything.

It's easy, just stick to business.

If obsession strikes, just do a PCABX DBT.

On Thu, 06 May 2004 13:40:48 -0400, agent86
wrote:

I'm inclined to agree with you're point of view, Arny. But even if you buy
the argument about digital resolution vs decreasing gain, these boxes don't
even address that. All the gain adjustments STILL happen in the DAW. An
analog summing bus without faders or pot is NOT an analog mixer AFAIK.

Ironically, changing the gain in 'digital' is a multiplication
function, and that increases the word length and requires dither to go
back to the original word length, and all that.
Summation (the calculation replaced by this box of resistors) is
literally adding numbers in a processor, and as long as you keep up
with overflows (which may require double precision integers, but
that's not a lot of overhead), the result is always 'exact'.

I suppose the reason these things are made is because people can
hear the difference, and many people like what comes out of the
resistor box better than what comes out of a digitally summed bus. I
hesistate to even post in this thread, because I don't think I can
hear the difference myself, and that seems to be the big criterion
here on RAP.

Perhaps the difference is in two D/A converters (giving the exact
same distortion to everything) vs. 8 or 16 D/A converters (each one
does something slightly different to the signal its carrying), but
that's just a hypothesis.

-----
http://mindspring.com/~benbradley

Thanks for the compliment, but I stink at electronics! It baffles me.
For some unexplainable reason, I do have "skill" at soldering. But I
have no idea what I'm wiring up. I need to be told, "do this do
that".


You could build a switchbox like this yourself, and if you remember to only
switch inputs to left or right, not both, getting center stuff by panning,
you could get very nice results, and use up a wad of solder. Of course, then
your results will depend on the quality of your D/A converters.

Peace,
Paul

In article writes:

Thanks for the compliment, but I stink at electronics! It baffles me.
For some unexplainable reason, I do have "skill" at soldering. But I
have no idea what I'm wiring up. I need to be told, "do this do
that".

That's what you get for the $1,000. g


--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

and thanks for all the insights guys. Paul, I appreciate your
thoughts on the crosstalk and noise. I'm really anti-noise and
crosstalk. It's like kryptonite to me. So thanks for the warning!