15 Aug
2009
15 Aug
'09
5:04 p.m.
Is it wrong to use a regular cable (no transformer) to connect the XLR
main and submix group outputs of a console to the TRS (balanced) inputs
of an audio card, or should impedance matching be done in that case?
It is quite common in music stores these days to find cables that are
XLR male on one end and TRS male on the other. (I'm currently using
those on my mixer outputs.) The cables *are* balanced, but they do not
contain a transformer at all.
The impedance of my console's main/submix outputs is rated as less than
75 ohms, but the input impedance of my audio card is 10k ohm. This
would seem to almost answer the question by itself, it weren't for the
near impossibility of actually finding a matching transformer that's TRS
and not TS on its 1/4" end. I looked at a lot of them. They're all
made for hooking up guitars, amps, and mics, and they all seem to have
an unbalanced plug opposite from the XLR end.
If there is indeed a need transformers on each XLR mixer output in this
instance, where can I get one that won't unbalance the connection in the
process? Or is it fine to just use these common XLR->TRS cables that
don't have any? The reason I started to investigate this is because I'm
not sure I'm not getting some of the "tone suck" you might associate
with a badly matched connection, and this seems a likely cause.
Addendum: On the realtime end of things, I'm now achievable a solid,
unbreakable 2ms. I can't seem to do anything that causes an xrun.
That's good at least!
--
+ Brent A. Busby + "We've all heard that a million monkeys
+ UNIX Systems Admin + banging on a million typewriters will
+ University of Chicago + eventually reproduce the entire works of
+ Physical Sciences Div. + Shakespeare. Now, thanks to the Internet,
+ James Franck Institute + we know this is not true." -Robert Wilensky
15 Aug
15 Aug
6:10 p.m.
Hi,
On Saturday 15 August 2009 21:04:22 Brent Busby wrote:
Is it wrong to use a regular cable (no transformer) to
connect the XLR
main and submix group outputs of a console to the TRS (balanced) inputs
of an audio card, or should impedance matching be done in that case?
It is quite common in music stores these days to find cables that are
XLR male on one end and TRS male on the other. (I'm currently using
those on my mixer outputs.) The cables *are* balanced, but they do not
contain a transformer at all.
The impedance of my console's main/submix outputs is rated as less than
75 ohms, but the input impedance of my audio card is 10k ohm. This
would seem to almost answer the question by itself, it weren't for the
near impossibility of actually finding a matching transformer that's TRS
and not TS on its 1/4" end. I looked at a lot of them. They're all
made for hooking up guitars, amps, and mics, and they all seem to have
an unbalanced plug opposite from the XLR end.
There is absolutely no need to do any transformation in that chain. Balanced
to balanced is pretty good.
Afaik impedance-matching doesn't necessarily mean that all impedances have to
be the same, they have to match. So if the output of the mixer has <75Ohm
compared to the input impedance of the soundcard of 10kOhm, it means that
almost no energy is lost at the output and all is "lost" at the input. And you
want the energy of the signal to be lost at the input so you can use it. This
is when you need the signal, not the power. For speakers (and for solar-
modules) you want the impedances to be about the same so the efficiency is high.
For more I have to get out my "physics for engineers"-book...
Have fun,
Arnold
6:44 p.m.
On Sat, Aug 15, 2009 at 10:10:51PM +0200, Arnold Krille wrote:
For speakers you want the impedances to be about the
same
so the efficiency is high.
No. Power amps have very low output impedance, typically less
than 0.1 ohm. Speakers are voltage-driven. They have to be for
good damping. You can easily 'feel' the difference. Disconnect
a speaker and gently tap the cone, you will feel it's 'soft',
and it may even produce some low frequency tone. Now connect
it to the amp and switch on the amp. The cone will feel quite
'hard'. What you feel now is the low impedance of the amp which
allows it to control the movement of the cone - it makes the
speaker resist any movement that is not driven by the amp.
Ciao,
--
FA
Io lo dico sempre: l'Italia è troppo stretta e lunga.
6:11 p.m.
On Sat, 2009-08-15 at 14:04 -0500, Brent Busby wrote:
It's fine. All pro audio balanced connections are low impedance outs
to high impedance ins. This is done so that you can mult outputs (make
copies) and the inputs won't mind a lower dB input signal.
Rich...
Is it wrong to use a regular cable (no transformer) to
connect the XLR
main and submix group outputs of a console to the TRS (balanced) inputs
of an audio card, or should impedance matching be done in that case?
It is quite common in music stores these days to find cables that are
XLR male on one end and TRS male on the other. (I'm currently using
those on my mixer outputs.) The cables *are* balanced, but they do not
contain a transformer at all.
The impedance of my console's main/submix outputs is rated as less than
75 ohms, but the input impedance of my audio card is 10k ohm. This
would seem to almost answer the question by itself, it weren't for the
near impossibility of actually finding a matching transformer that's TRS
and not TS on its 1/4" end. I looked at a lot of them. They're all
made for hooking up guitars, amps, and mics, and they all seem to have
an unbalanced plug opposite from the XLR end.
If there is indeed a need transformers on each XLR mixer output in this
instance, where can I get one that won't unbalance the connection in the
process? Or is it fine to just use these common XLR->TRS cables that
don't have any? The reason I started to investigate this is because I'm
not sure I'm not getting some of the "tone suck" you might associate
with a badly matched connection, and this seems a likely cause.
Addendum: On the realtime end of things, I'm now achievable a solid,
unbreakable 2ms. I can't seem to do anything that causes an xrun.
That's good at least!
6:17 p.m.
Impedance matching ditty :)
Low to High, the signals fly.
High to Low, a big No No
--
Will J Godfrey
http://www.musically.me.uk
7:48 p.m.
Thanks to all for the info! The new DAW is coming along nicely...
--
+ Brent A. Busby + "We've all heard that a million monkeys
+ UNIX Systems Admin + banging on a million typewriters will
+ University of Chicago + eventually reproduce the entire works of
+ Physical Sciences Div. + Shakespeare. Now, thanks to the Internet,
+ James Franck Institute + we know this is not true." -Robert Wilensky
6:18 p.m.
On Sat, 2009-08-15 at 14:04 -0500, Brent Busby wrote:
Is it wrong to use a regular cable (no transformer) to
connect the XLR
main and submix group outputs of a console to the TRS (balanced) inputs
of an audio card, or should impedance matching be done in that case?
It is quite common in music stores these days to find cables that are
XLR male on one end and TRS male on the other. (I'm currently using
those on my mixer outputs.) The cables *are* balanced, but they do not
contain a transformer at all.
The impedance of my console's main/submix outputs is rated as less than
75 ohms, but the input impedance of my audio card is 10k ohm. This
would seem to almost answer the question by itself, it weren't for the
near impossibility of actually finding a matching transformer that's TRS
and not TS on its 1/4" end. I looked at a lot of them. They're all
made for hooking up guitars, amps, and mics, and they all seem to have
an unbalanced plug opposite from the XLR end.
It's not a problem.
The convention nowadays is for low impedance outputs and high impedance
inputs.
We are concerned with voltage, rather than power transfer here, so not
loading the output is a good thing.
http://en.wikipedia.org/wiki/Impedance_bridging
If there is indeed a need transformers on each XLR mixer output in this
instance, where can I get one that won't unbalance the connection in the
process? Or is it fine to just use these common XLR->TRS cables that
don't have any? The reason I started to investigate this is because I'm
not sure I'm not getting some of the "tone suck" you might associate
with a badly matched connection, and this seems a likely cause.
Addendum: On the realtime end of things, I'm now achievable a solid,
unbreakable 2ms. I can't seem to do anything that causes an xrun.
That's a tricky one. You could try switching to a USB soundcard, and
using a hub with multiple devices attached. Removing and adding USB
devices while recording then may help to increase the incidence of
xruns.
If that doesn't work, the only recourse may be to use a slower processor
and an older motherboard. Also, try to find the most obscure and least
Linux compatible PCI and video cards you can, and put as many of them in
the machine as possible.
That's good at least!
6:29 p.m.
On Sat, 15 Aug 2009 21:18:16 +0100
philicorda <philicorda(a)ntlworld.com> wrote:
That's a tricky one. You could try switching to a
USB soundcard, and
using a hub with multiple devices attached. Removing and adding USB
devices while recording then may help to increase the incidence of
xruns.
If that doesn't work, the only recourse may be to use a slower processor
and an older motherboard. Also, try to find the most obscure and least
Linux compatible PCI and video cards you can, and put as many of them in
the machine as possible.
You own me a keyboard!
--
Will J Godfrey
http://www.musically.me.uk
7:50 p.m.
On Sat, 15 Aug 2009, philicorda wrote:
Well...
I should have said, "can't seem to do anything that I'd really want to
casually do on my desktop without going crazy..." :)
--
+ Brent A. Busby + "We've all heard that a million monkeys
+ UNIX Systems Admin + banging on a million typewriters will
+ University of Chicago + eventually reproduce the entire works of
+ Physical Sciences Div. + Shakespeare. Now, thanks to the Internet,
+ James Franck Institute + we know this is not true." -Robert Wilensky
Addendum: On
the realtime end of things, I'm now achievable a solid,
unbreakable 2ms. I can't seem to do anything that causes an xrun.
That's a tricky one. You could try switching to a USB soundcard, and
using a hub with multiple devices attached. Removing and adding USB
devices while recording then may help to increase the incidence of
xruns.
If that doesn't work, the only recourse may be to use a slower
processor and an older motherboard. Also, try to find the most obscure
and least Linux compatible PCI and video cards you can, and put as
many of them in the machine as possible.
6:31 p.m.
On Sat, Aug 15, 2009 at 02:04:22PM -0500, Brent Busby wrote:
Is it wrong to use a regular cable (no transformer) to
connect the XLR
main and submix group outputs of a console to the TRS (balanced) inputs
of an audio card, or should impedance matching be done in that case?
It is quite common in music stores these days to find cables that are
XLR male on one end and TRS male on the other. (I'm currently using
those on my mixer outputs.) The cables *are* balanced, but they do not
contain a transformer at all.
You don't need impedance matching. The only place where it
is still required for audio signals is when you're driving
long rented telephone lines form e.g. an OB van to a broad-
casting center. In that case you need to match both the output
and input to the line impedance. But probably nobody is still
doing that today, it's all digital.
Also when the input is balanced you won't need a transformer
except when the two units being connected are on separate
power systems and you could have a ground difference.
The impedance of my console's main/submix outputs
is rated as less than
75 ohms, but the input impedance of my audio card is 10k ohm.
That's how all pro audio equipment has been designed for the
last 40 years or so. Output impedance < 100 ohm, inputs > 10k.
It's perfectly OK to connect the two. The high impedance ratio
means the output won't 'feel' the input, and you can split the
signal to more than one input without any gain change.
Ciao,
--
FA
Io lo dico sempre: l'Italia è troppo stretta e lunga.
5573
days inactive
5573
days old
linux-audio-user@lists.linuxaudio.org
9 comments
6 participants
participants (6)
-
Arnold Krille -
Brent Busby -
Folderol -
Fons Adriaensen -
philicorda -
Ricardus Vincente