Is the impedance of a balanced cable less than the impedan..

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In article <20041105085718.11419.00000116@mb-m29.aol.com>,
Leoaw3 <leoaw3@aol.comnospam> wrote:
>Sorry to waste time on such a basic question - but I'm just not understanding.
>
>I tend to run balanced cables for just about everything - unbalanced only
>occasionally for very short cables. But I thought the prime issue was external
>noise coupling into the cable. Do balanced cables inherently have a lower
>impedance than unbalanced?

No.

This is discussed in the FAQ... the idea with balanced cables is basically
that there are two opposing signals being sent down the line, and what the
input looks at is the difference between them. When noise is induced, it is
induced into both lines, and so it gets cancelled out.

Impedance has nothing to do with it... you can have high-Z balanced lines
and low-Z unbalanced lines (although they are not as common).
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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The "characteristic impedance" of a cable -- balanced or unbalanced -- is
determined by a number of factors that are under control of the cable designer.
One type of cable is not inherently higher- or lower-impedance than the other.
(In fact, I've never seen a balanced cable with a spec'd characteristic
impedance.) The characteristic impedance is not generally seen as a significant
performance factor at audio frequencies.

Do not confuse the cable's characteristic impedance with the resistance of its
conductors. They have nothing to do with each other.

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In article <cmg233$ik6$1@panix2.panix.com>, kludge@panix.com (Scott Dorsey)
wrote:

> In article <20041105085718.11419.00000116@mb-m29.aol.com>,
> Leoaw3 <leoaw3@aol.comnospam> wrote:
> >Sorry to waste time on such a basic question - but I'm just not
> >understanding.
> >
> >I tend to run balanced cables for just about everything - unbalanced only
> >occasionally for very short cables. But I thought the prime issue was
> >external
> >noise coupling into the cable. Do balanced cables inherently have a lower
> >impedance than unbalanced?
>
> No.
>
> This is discussed in the FAQ... the idea with balanced cables is basically
> that there are two opposing signals being sent down the line, and what the
> input looks at is the difference between them. When noise is induced, it is
> induced into both lines, and so it gets cancelled out.
>
> Impedance has nothing to do with it... you can have high-Z balanced lines
> and low-Z unbalanced lines (although they are not as common).
> --scott

I attended Bill Whitlock's tutorial at the AES and this is at odds with his
definition of a balanced system. He says that it is the balance between source
and load impedances that determines whether a system is balanced or not and that
the differential nature of the signals is irrelevent.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x---------- http://ccrma.stanford.edu/~jay/ ------------x

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"Jay Kadis" <jay@ccrma.stanford.edu> wrote in message
news:jay-143DE0.07491605112004@news.stanford.edu...
> In article <cmg233$ik6$1@panix2.panix.com>, kludge@panix.com (Scott
> Dorsey)
> wrote:
>
>> In article <20041105085718.11419.00000116@mb-m29.aol.com>,
>> Leoaw3 <leoaw3@aol.comnospam> wrote:
>> >Sorry to waste time on such a basic question - but I'm just not
>> >understanding.
>> >
>> >I tend to run balanced cables for just about everything - unbalanced
>> >only
>> >occasionally for very short cables. But I thought the prime issue was
>> >external
>> >noise coupling into the cable. Do balanced cables inherently have a
>> >lower
>> >impedance than unbalanced?
>>
>> No.
>>
>> This is discussed in the FAQ... the idea with balanced cables is
>> basically
>> that there are two opposing signals being sent down the line, and what
>> the
>> input looks at is the difference between them. When noise is induced, it
>> is
>> induced into both lines, and so it gets cancelled out.
>>
>> Impedance has nothing to do with it... you can have high-Z balanced lines
>> and low-Z unbalanced lines (although they are not as common).
>> --scott
>
> I attended Bill Whitlock's tutorial at the AES and this is at odds with
> his
> definition of a balanced system. He says that it is the balance between
> source
> and load impedances that determines whether a system is balanced or not
> and that
> the differential nature of the signals is irrelevent.

I think you misunderstood.

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"Scott Dorsey" wrote ...
> Jay Kadis wrote:
>>I attended Bill Whitlock's tutorial at the AES and this is at
>>odds with his definition of a balanced system. He says that
>> it is the balance between source and load impedances that
>>determines whether a system is balanced or not and that
>>the differential nature of the signals is irrelevent.
>
> That's very much true... as long as the impedances are the
> same, the noise will be induced in the two lines in the same
> way. And it is the differential_input_ subtracting the noise
> common to the two lines that makes the system balanced.

Jay seems to be talking about impedance matching between
OUTput and INput, and Scott seems to be talking about
impedance matching between the two differential input
nodes. My study and experience agrees more with Scott's
explanation than with Jay's (and his interperetation of
Whitlock).

In modern solid-state equipment where output impedances
are quite low, why does the output impedance match with
the input impedance have anything to do with noise rejection?
It seems to be almost entirely up to the input to reject
whatever inappropriate signal.

And isn't Whitlock's POV from a world of equipment which
uses proper transformers at each input and output? Alas not
likely to be found in the real world.

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In article <10on9bhe3gn8obc@corp.supernews.com>,
"Richard Crowley" <rcrowley7@xprt.net> wrote:

> "Scott Dorsey" wrote ...
> > Jay Kadis wrote:
> >>I attended Bill Whitlock's tutorial at the AES and this is at
> >>odds with his definition of a balanced system. He says that
> >> it is the balance between source and load impedances that
> >>determines whether a system is balanced or not and that
> >>the differential nature of the signals is irrelevent.
> >
> > That's very much true... as long as the impedances are the
> > same, the noise will be induced in the two lines in the same
> > way. And it is the differential_input_ subtracting the noise
> > common to the two lines that makes the system balanced.
>
> Jay seems to be talking about impedance matching between
> OUTput and INput, and Scott seems to be talking about
> impedance matching between the two differential input
> nodes. My study and experience agrees more with Scott's
> explanation than with Jay's (and his interperetation of
> Whitlock).
>

No, I meant both the source/load balance AND the matching of the
inverting/noninverting impedances.

> In modern solid-state equipment where output impedances
> are quite low, why does the output impedance match with
> the input impedance have anything to do with noise rejection?
> It seems to be almost entirely up to the input to reject
> whatever inappropriate signal.
>

The balance between the source and load impedances IS critical in maintaing the
CMRR of the differential amplifier, but in the sense of matching both the
inverting and non-inverting impedances of the Wheatstone bridge that is created.

> And isn't Whitlock's POV from a world of equipment which
> uses proper transformers at each input and output? Alas not
> likely to be found in the real world.
>

Bill also has a patent on a bootstrapped balanced amplifier circuit, the IC
implementation of which was announced at the AES.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x---------- http://ccrma.stanford.edu/~jay/ ------------x

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On Fri, 05 Nov 2004 14:16:16 GMT, donaldun@spamfreepearce.uk.com (Don
Pearce) wrote:

>On 05 Nov 2004 13:57:18 GMT, leoaw3@aol.comnospam (Leoaw3) wrote:
>
>>Sorry to waste time on such a basic question - but I'm just not understanding.
>>
>>I tend to run balanced cables for just about everything - unbalanced only
>>occasionally for very short cables. But I thought the prime issue was external
>>noise coupling into the cable.

That's an important issue, but that also assumes the inputs and
outputs are balanced, as well as the cable. A lot of the 'semi-pro'
gear such as the Delta 44 and 66 cards are not actually balanced,
though the marketing may lead one to believe they are.
But even so, long runs of unbalanced cables (or more correctly,
unbalanced systems/connections, which may use "balanced" cables) often
don't pick up much noise in many circumstances. YMMV.

>>Do balanced cables inherently have a lower
>>impedance than unbalanced?
>>
>>Thanks MUCH,
>>-lee-
>
>In general the impedance of a balanced cable will be higher than that
>of an unbalanced one.

For practical purposes, audio cables themselves have infinite
impedance (perhaps the only notable exception is an guitar without an
internal preamp driving a long cable). It's the impedance of the
source and destination that count (and where the above generality is
true), not the cable.

>d
>Pearce Consulting
>http://www.pearce.uk.com

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

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Richard Crowley wrote:

> "Scott Dorsey" wrote ...
> > Jay Kadis wrote:
> >>I attended Bill Whitlock's tutorial at the AES and this is at
> >>odds with his definition of a balanced system. He says that
> >> it is the balance between source and load impedances that
> >>determines whether a system is balanced or not and that
> >>the differential nature of the signals is irrelevent.
> >
> > That's very much true... as long as the impedances are the
> > same, the noise will be induced in the two lines in the same
> > way. And it is the differential_input_ subtracting the noise
> > common to the two lines that makes the system balanced.
>
> Jay seems to be talking about impedance matching between
> OUTput and INput, and Scott seems to be talking about
> impedance matching between the two differential input
> nodes. My study and experience agrees more with Scott's
> explanation than with Jay's (and his interperetation of
> Whitlock).
>
> In modern solid-state equipment where output impedances
> are quite low, why does the output impedance match with
> the input impedance have anything to do with noise rejection?
> It seems to be almost entirely up to the input to reject
> whatever inappropriate signal.
>
> And isn't Whitlock's POV from a world of equipment which
> uses proper transformers at each input and output? Alas not
> likely to be found in the real world.

Alas ?

You *want* transformers messing up the signal every time it leaves or
enters equipment ?

Graham

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In article <418BEF23.C9CA905C@hotmail.com>,
Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote:

> Jay Kadis wrote:
>
> > I attended Bill Whitlock's tutorial at the AES and this is at odds with his
> > definition of a balanced system. He says that it is the balance between
> > source
> > and load impedances that determines whether a system is balanced or not and
> > that
> > the differential nature of the signals is irrelevent.
>
> The differential nature of the signals is hardly *irrelevant* !
>
> Regarding 'balance' between source and load, I'm not sure what you're
> referring to.
> Certainly 'matched impedance' ( load and source Z equal ) is *very* old hat
> and
> unknown in typical pro-audio gear. It *is* important for good balance that
> the load
> impedance is symmetrical about ground, which isn't the case sadly with most
> 'balanced' inputs using a single op-amp and equal value resistors for the
> inverting
> and non-inverting legs.
>
>
> Graham
>

I think that was his point, that the load impedance must be symmetrical. As far
as the signal being differential, what he meant was that you need not use an
inverted signal as well as a non-inverted one, as you would get the noise
rejection even if only one of the lines carried signal.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x---------- http://ccrma.stanford.edu/~jay/ ------------x

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Jay Kadis wrote:

> In article <418BEF23.C9CA905C@hotmail.com>,
> Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote:
>
> > Jay Kadis wrote:
> >
> > > I attended Bill Whitlock's tutorial at the AES and this is at odds with his
> > > definition of a balanced system. He says that it is the balance between
> > > source
> > > and load impedances that determines whether a system is balanced or not and
> > > that
> > > the differential nature of the signals is irrelevent.
> >
> > The differential nature of the signals is hardly *irrelevant* !
> >
> > Regarding 'balance' between source and load, I'm not sure what you're
> > referring to.
> > Certainly 'matched impedance' ( load and source Z equal ) is *very* old hat
> > and
> > unknown in typical pro-audio gear. It *is* important for good balance that
> > the load
> > impedance is symmetrical about ground, which isn't the case sadly with most
> > 'balanced' inputs using a single op-amp and equal value resistors for the
> > inverting
> > and non-inverting legs.
> >
> >
> > Graham
>
>
> I think that was his point, that the load impedance must be symmetrical.

Right. Makes sense. I bet most ppl don't realise that the typical x1 differential
op-amp configuration with 4x10k resistors places an asymmetric load on a balanced
line. I've even had ppl query my use of the correct values ( use 2x3k3 instead on
the non-inverting side ).

Having said that, since the source Z is typically in the 100 ohm region for many
outputs, the unbalance thus created is less than that caused by the possible
mismatch of the typically used 5% resistors !

> As far
> as the signal being differential, what he meant was that you need not use an
> inverted signal as well as a non-inverted one, as you would get the noise
> rejection even if only one of the lines carried signal.

Yes, that's true as long as the 'non-signal' line is correctly referred.


Graham

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"William Sommerwerck" <williams@nwlink.com> wrote in message
> The "characteristic impedance" of a cable -- balanced or unbalanced -- is
> determined by a number of factors that are under control of the cable designer.
> One type of cable is not inherently higher- or lower-impedance than the other.
> (In fact, I've never seen a balanced cable with a spec'd characteristic
> impedance.) The characteristic impedance is not generally seen as a significant performance factor at audio frequencies.

Let's not forget digital audio. AES/EBU does require 110 ohm cable.
SPDIF requires 75 ohm cable. "Characteristic imedance" that is.


> Do not confuse the cable's characteristic impedance with the resistance of its
> conductors. They have nothing to do with each other.

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In article <20041105085718.11419.00000116@mb-m29.aol.com> leoaw3@aol.comnospam writes:

> I thought the prime issue was external
> noise coupling into the cable. Do balanced cables inherently have a lower
> impedance than unbalanced?

No. And at audio frequencies and for typical studio lengths, the
impedance of the cable doesn't matter anyway. However, balanced cables
connect to balanced inputs, and with balanced sources, there's better
rejection of external noise.

--
I'm really Mike Rivers (mrivers@d-and-d.com)
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 here: double-m-eleven-double-zero at yahoo

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Mike Rivers wrote:

> In article <jay-143DE0.07491605112004@news.stanford.edu> jay@ccrma.stanford.edu writes:
>
> > I attended Bill Whitlock's tutorial at the AES and this is at odds with his
> > definition of a balanced system. He says that it is the balance between source
> >
> > and load impedances that determines whether a system is balanced or not and
> > that
> > the differential nature of the signals is irrelevent.
>
> The input must be differential for common mode noise reject to work.
> The source need not be differential (you don't need one lead going
> positive with respect to ground while the other one goes negative with
> respect to ground by the same amount). The only requirement is that
> when looking back "upstream" to the source, each conductor of the pair
> has the same impedance to ground (or the audio reference point).
>
> This is why companies that hang a resistor between Pin 3 of an XLR
> output (or the Ring of a TRS jack) and ground aren't lying when they
> say that the output is balanced, even though onlyt Pin 2/Tip are
> driven.

I would only call that configuration impedance balanced or quasi-balanced. But then I don't
like fibbing about specs.

Not to be confused with 'ground sensing' outputs that use pin 3 to detect any ground
differential between equipment A and B and apply a 'correction signal'. Costs a few more
resistors around the op-amp output..


Graham :-)

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Scott Dorsey wrote:

> Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote:
> >
> >At audio frequencies a cable has no 'characteristic impedance'. The wavelength at
> >audio frequencies is far too long relative to typical cable lengths.
>
> Why do I get echos when I call long distance, then?

You still do ? Been ages since I heard that stuff. Is the US not yet converted
throughout to digital exchanges ?

When I referred to typical cable lengths I had a studio / live sound application in
mind rather than telephony which may involve somewhat large cable lengths.

I appreciate that long 'landlines' operate differently to a 30ft mic cable. I've seen
them being EQ'd for quality audio links.

> >What's more, many balanced circuits operate at *lower* impedances than unbalanced
> >ones !
>
> Absolutely.

Graham

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On Sat, 06 Nov 2004 06:57:25 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:

>Don Pearce wrote:
>
>> On Fri, 05 Nov 2004 21:17:31 +0000, Pooh Bear
>> <rabbitsfriendsandrelations@hotmail.com> wrote:
>>
>> >Don Pearce wrote:
>> >
>> >> On 05 Nov 2004 13:57:18 GMT, leoaw3@aol.comnospam (Leoaw3) wrote:
>> >>
>> >> >Sorry to waste time on such a basic question - but I'm just not understanding.
>> >> >
>> >> >I tend to run balanced cables for just about everything - unbalanced only
>> >> >occasionally for very short cables. But I thought the prime issue was external
>> >> >noise coupling into the cable. Do balanced cables inherently have a lower
>> >> >impedance than unbalanced?
>> >> >
>> >> >Thanks MUCH,
>> >> >-lee-
>> >>
>> >> In general the impedance of a balanced cable will be higher than that
>> >> of an unbalanced one.
>> >
>> >What drugs are you on ?
>> >
>> >At audio frequencies a cable has no 'characteristic impedance'. The wavelength at
>> >audio frequencies is far too long relative to typical cable lengths.
>> >
>> >What's more, many balanced circuits operate at *lower* impedances than unbalanced
>> >ones !
>> >
>> >
>> >Graham
>>
>> 1. Cables have characteristic impedances at all frequencies. They
>> merely have little or no relevance at audio frequencies.
>> 2. Given otherwise similar geometries, the impedance of a balanced
>> cable is higher than that of an unbalanced cable.
>> 3. The question is about cables, not circuits.
>
>The correct *answer* is that cables play no important role in this debate. It's
>entirely the circuits that determine operation.
>
>
>Graham

See my answer number 1. And thank you for your retraction.

d
Pearce Consulting
http://www.pearce.uk.com

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In article <418C7551.220C6D68@hotmail.com> rabbitsfriendsandrelations@hotmail.com writes:

> > This is why companies that hang a resistor between Pin 3 of an XLR
> > output (or the Ring of a TRS jack) and ground aren't lying when they
> > say that the output is balanced, even though onlyt Pin 2/Tip are
> > driven.
>
> I would only call that configuration impedance balanced or quasi-balanced. But
> then I don't
> like fibbing about specs.

No, this is balanced. Period. I started using the term "impedance
balanced" (in fact I may have invented it, though I don't claim to be
the only one to invent the term) to distinguish such an output
configuration for people who expect a balanced output to have both
sides of the line driven with a signal with respect to ground. (But
then, how do you explain a transformer output which has only leakage
to give you any signal referenced to ground to those people?)

> Not to be confused with 'ground sensing' outputs that use pin 3 to detect any
> ground
> differential between equipment A and B and apply a 'correction signal'. Costs a
> few more
> resistors around the op-amp output..

That's yet another scheme, but it's to give a differential output.
Then there's the single ended output with an inverter going to the
other lead to give a differential output - but those outputs are
rarely balanced because the impedance looking back into the two active
lines isn't the same. But to someone who looks only for voltage, it
looks like a "balanced" output.

The point that Bill Whitlock makes is that balanced and differential
outputs are different and that having one does not mean that you have
the other (or at least an effective version of the other).


--
I'm really Mike Rivers (mrivers@d-and-d.com)
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 here: double-m-eleven-double-zero at yahoo

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In article <jr1qo0t6u8mbmpp8eccqm7tl151pb5sqqg@4ax.com> chrishornbeckremovethis@att.net writes:

> My gripe is with the limitations of the term "differential input".
> Of course we all know what it means, but *all inputs* are
> differential. What is a better term for three pin inputs?

Oh, man! Now you REALLY want to confuse people. <g<>


--
I'm really Mike Rivers (mrivers@d-and-d.com)
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 here: double-m-eleven-double-zero at yahoo

Archived from groups: rec.audio.pro (More info?)

> The natural result of revisionism. I'd be fascinated to
> see an explanation of how "all inputs are differential".

Simple. An unbalanced input senses the difference between ground and the signal
line. In that sense it is "differential."

This is why unbalanced lines are so susceptible to hum and ground loops -- the
ground is not absolute; it can be altered.

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"William Sommerwerck" <williams@nwlink.com> wrote in message
news:10ose4b4urgadf5@corp.supernews.com...
>> The natural result of revisionism. I'd be fascinated to
>> see an explanation of how "all inputs are differential".
>
> Simple. An unbalanced input senses the difference between ground and the
> signal
> line. In that sense it is "differential."
>
> This is why unbalanced lines are so susceptible to hum and ground loops --
> the
> ground is not absolute; it can be altered.
>

Archived from groups: rec.audio.pro (More info?)

>> Simple. An unbalanced input senses the difference between
>> ground and the signal line. In that sense it is "differential."

> Yes, and "that sense" is what practically nullifies the meaning
> of differential. Exactly what I meant by revisionisim diluting
> the meaning of our language. But perhaps it is so pervasive
> that people don't notice it anymore. Too bad.

Right. "Differential" implies that the two inputs are "floating" -- neither is a
reference.