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Recording live question; splitting the signal

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July 26, 2005 10:39:48 PM

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

I'd like to tap off the house snake to feed a multitrack recorder through a
set of dedicated mic preamps. The preamps I'm looking at have an input
impedance of 2K ohms. Can I get good results from using simple cable
splitters, or do I need mic splitters with transformer isolation? I've
sampled some specs, and a lot of boards seem to have an input impedance in
the same general range as my pre's (1.3K to 3K). The isolation splitters
are spendy, but if I need to use them to get clean recordings without
messing with the signal to the FOH board I will. All advice is appreciated.

Cheers,
Walt
Anonymous
July 27, 2005 12:41:48 AM

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

"WJ" wrote ...
> I'd like to tap off the house snake to feed a multitrack recorder
> through a set of dedicated mic preamps. The preamps I'm
> looking at have an input impedance of 2K ohms. Can I get
> good results from using simple cable splitters, or do I need
> mic splitters with transformer isolation? I've sampled some
> specs, and a lot of boards seem to have an input impedance in
> the same general range as my pre's (1.3K to 3K). The isolation
> splitters are spendy, but if I need to use them to get clean
> recordings without messing with the signal to the FOH board
> I will. All advice is appreciated.

Under ideal conditions, you likely can get good signals from the
mics without impacting the FOH operation. However, in the REAL
world, no FOH engineer worth his reputation is going to let you do
that without a lot of pre-work, testing, assurances, track record,
reputation, etc. etc., and most of the ones I know wouldn't allow it
under any circumstances.

There are just too many pitfalls, particularly in a live performance,
to make this a viable plan. It is more a matter of joining the two
systems together harmoniously (mainly shielding/grounding/
isolation) much more than just the matter of load impedance.

If you don't want to buy/build a splitting transformer solution, rent
it for the occasion. You aren't the first person to find themselves in
this exact situation, and you won't be the last.
Anonymous
July 27, 2005 2:07:29 AM

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

WJ wrote:
> I'd like to tap off the house snake to feed a multitrack recorder through a
> set of dedicated mic preamps. The preamps I'm looking at have an input
> impedance of 2K ohms. Can I get good results from using simple cable
> splitters, or do I need mic splitters with transformer isolation? I've
> sampled some specs, and a lot of boards seem to have an input impedance in
> the same general range as my pre's (1.3K to 3K). The isolation splitters
> are spendy, but if I need to use them to get clean recordings without
> messing with the signal to the FOH board I will. All advice is appreciated.

For most mics, impedance won't be an issue - though it can be with some,
especially if the feed is being split to three or four inputs rather than
just two. I ran into a real problem with a KMS105 once because of that
(though to be fair to Neuman, it was probably a badly designed mixer that
actually caused all the trouble).

Isolation is always a good idea if you can get it, and occasionally it
will turn out to be a necessity. But in general, you can get by without
isolation most of the time if you're careful to avoid ground loops.
That's the biggest risk in going without isolation. So make sure that
everyone who is sharing the mic feed is also drawing their power from the
same circuit, or from circuits that share a common earth ground.
Related resources
Anonymous
July 27, 2005 3:55:20 AM

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

In article <mpadneVvoNZ9eHvfRVn-uA@comcast.com>, WJ <waltj@hotmail.com> wrote:
>I'd like to tap off the house snake to feed a multitrack recorder through a
>set of dedicated mic preamps. The preamps I'm looking at have an input
>impedance of 2K ohms. Can I get good results from using simple cable
>splitters, or do I need mic splitters with transformer isolation? I've
>sampled some specs, and a lot of boards seem to have an input impedance in
>the same general range as my pre's (1.3K to 3K). The isolation splitters
>are spendy, but if I need to use them to get clean recordings without
>messing with the signal to the FOH board I will. All advice is appreciated.

Maybe you can get by with Y cables. It depends on how careful your
grounding is, how much of a noise problem you've got, and what kind
of microphones you are using. It also depends on political issues.

Splitters solve all of these problems, although splitters with one
direct and one isolated output sometimes don't solve all the political
ones.

Most PA rental places have a splitter available for rental, since it
is one of those things that most people don't use enough to have their
own around.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
July 27, 2005 6:08:11 AM

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

On Tue, 26 Jul 2005 18:39:48 -0700, "WJ" <waltj@hotmail.com> wrote:

>I'd like to tap off the house snake to feed a multitrack recorder through a
>set of dedicated mic preamps. The preamps I'm looking at have an input
>impedance of 2K ohms. Can I get good results from using simple cable
>splitters, or do I need mic splitters with transformer isolation? I've
>sampled some specs, and a lot of boards seem to have an input impedance in
>the same general range as my pre's (1.3K to 3K). The isolation splitters
>are spendy, but if I need to use them to get clean recordings without
>messing with the signal to the FOH board I will. All advice is appreciated.

Having been through a similar dealio myself, I'd want to ask
two questions:

Can you live with the phantom (for example, DI's and such,
and maybe condenser piano mic's) power on the mic lines?

And, more importantly, will the FOH folks give you the
access that you expect? They have lotsa good reasons not to.

The answers to these questions are neither obvious or
necessarily believiable.

Good fortune,

Chris Hornbeck
Anonymous
July 27, 2005 6:47:20 AM

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

"WJ" <waltj@hotmail.com> writes:

>I'd like to tap off the house snake to feed a multitrack recorder through a
>set of dedicated mic preamps. The preamps I'm looking at have an input
>impedance of 2K ohms. Can I get good results from using simple cable
>splitters, or do I need mic splitters with transformer isolation? I've
>sampled some specs, and a lot of boards seem to have an input impedance in
>the same general range as my pre's (1.3K to 3K). The isolation splitters
>are spendy, but if I need to use them to get clean recordings without
>messing with the signal to the FOH board I will. All advice is appreciated.

I'm in/was just in the same boat. First off, good luck convincing the FOH
engineer that you can hard-Y off his/her microphones without isolation. I
talked with Michael Grace about this and technically it can be done, but
indeed there are pitfalls with loading, grounding and such; plus, if
you're running a snake to the split you're adding in your cable's
capacitance to the overall system. You have the possibility
of degrading the signal for all -- how much depends on a lot of factors.

I was looking at perhaps using Grace's new remote-controlled preamp and
locating it at a hard Y split right at the PA company's stage box. This
new model pre has a 5K input Z, so with that and a few feet of cable I
probably could convince the FOH folks to let me do a hard split. (But even
when they know you by reputation and have checked you out with your
clients they are a suspicious bunch, and I don't blame them.)

OTOH, with that preamp we're not talking about a cheap solution (and
neiher are transformers, but they give full protection).

I've also contemplated finding some higher-Z transformers and accepting a
lower signal strength just so that the FOH folks can be assured I won't
screw up their signal. As most of the time I'd only need this is for the
rare rock/pop gigs, I figured there's plenty of signal strength available
so that I could take a 10-12 dB hit.

In small PA settings with acoustic groups who carry a small reinforcement
PA, I've used my mics and pres and returned signals Y'd from the outputs
of my pres to their PA, padded down and run through my bridging
transformers, shields lifted at my end through a resistor and cap. That
*really* takes trust, but you have full control of the preamplification
stage; but they still see a mic signal at their on-stage porta mixer and
can be made happy. This has been very clean, but I only have a few
channels of this available.

Just did a rock gig where a big splitter was rented. Jensen transformers
throughout; worked well. No hum/buzz other than what the PA guys were
chasing on their side. All shields lifted on my side (they had the direct
through and supplied phantom), and my system was squeaky clean. I did use
some of my mics on drums, and had a few other of my mics ready to zip in
if something couldn't get into the splitter (sometimes they took line outs
of guitar heads and ran back to their board via 1/4 phone plugs. Yikes. No
lift switches that I saw; maybe that explained some of the buzz. Nice
folks, though.)

I'll be curious to see the solutions/ideas posted by others.

Frank Stearns
Mobile Audio
--
.
July 27, 2005 9:04:04 AM

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

Gentlemen, thanks for your responses. These aren't pro gigs for me yet, but
things appear to be moving in that direction. Since I don't have an
audio-god reputation and long client list, it seems the way to present a
professional image--and insure minimal impact on the house system--would be
to either own or rent an isolation splitter. I'll look into renting, but
considering my location, saving the pickup/return time would pay for a
splitter before too long. I've been looking at a Whirlwind unit: the
SB24T11G. It features 24 channels straight-through and an isolated split
with ground lifts on each channel. Can anyone comment on the quality of
Whirlwind gear? I've always had good experiences with them.

Thanks again,
Walt
Anonymous
July 27, 2005 1:30:40 PM

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

In article <Xr2dnWk8x5Ot5XrfRVn-rA@comcast.com>, WJ <waltj@hotmail.com> wrote:
>Gentlemen, thanks for your responses. These aren't pro gigs for me yet, but
>things appear to be moving in that direction. Since I don't have an
>audio-god reputation and long client list, it seems the way to present a
>professional image--and insure minimal impact on the house system--would be
>to either own or rent an isolation splitter. I'll look into renting, but
>considering my location, saving the pickup/return time would pay for a
>splitter before too long. I've been looking at a Whirlwind unit: the
>SB24T11G. It features 24 channels straight-through and an isolated split
>with ground lifts on each channel. Can anyone comment on the quality of
>Whirlwind gear? I've always had good experiences with them.

It's good, but remember that you can order the Whirlwind gear in a dozen
different configurations. You can get everything with XLRs, or you can
get multipin connectors with pigtails. You can get one isolated output
and one direct, or two isolated outputs with external phantom. You can
get Jensen transformers or their generics (which aren't bad, but are not
as clean as the Jensens).
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
July 27, 2005 4:37:18 PM

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

In article <Xr2dnWk8x5Ot5XrfRVn-rA@comcast.com> waltj@hotmail.com writes:

> Gentlemen, thanks for your responses. These aren't pro gigs for me yet, but
> things appear to be moving in that direction. Since I don't have an
> audio-god reputation and long client list, it seems the way to present a
> professional image--and insure minimal impact on the house system--would be
> to either own or rent an isolation splitter.

That's correct. If there's a PA company doing the show (usually not in
a club, but usually in a concert unless the venue has its own sound
system) find out who's supplying the sound equpment and ask if they
can provide a splitter. You might find that there's already going to
be one for the monitor console and there's a spare set of outputs that
you can use. Advance work is really important when doing remote
recordings.

The advantage of getting the PA doing the show to provide the splitter
is that they won't worry about it. If you show up with a junky looking
box that you rented elsewhere, they might be suspicious. After all, if
a channel goes out because of a short in your splitter, the audience
will be staring at the person at the PA console, not you.



--
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
July 29, 2005 1:42:56 AM

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

<blink blink> Dang.

Sorry about the system clock screwup. I'm not sure how that happened...
Anonymous
July 29, 2005 4:40:28 AM

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

I just sold a pair of Horizon MS-4 splitters that I never used in the
two years that I had them. They're great rack mounted splitters with
all the goodies: isolation, ground lift, parallel out, etc., and
apparently pass phantom power. I bought them because at a prior gig I
needed to split a mic and used a $15 splitter cable. All was well, but
I wanted to be ready for the big time.

Anyway, just thinking of hauling eight channels of splitters and at
least 16 mic cables into a club would drive a soundperson bonkers.
That's a lot of work for both parties involved and a lot of uncertainty
for a soundperson who probably doesn't want to deal with all that,
especially if those aren't Monster cables being sent back to the board.

So I settled on taking line feeds off the board, e.g., direct outs,
inserts half way, aux sends, submix, etc. Granted, I'm at the mercy of
the board and have to use the board's mic pres, but it's the simplest
and quickest way to interact with an already nervous soundperson.

Nevertheless, if politics is not an issue my vote is for the
transformer mic splitters. If you can break the snake, the mic signal
gives you total control over your recording. Good luck.

WJ wrote:
> I'd like to tap off the house snake to feed a multitrack recorder through a
> set of dedicated mic preamps. The preamps I'm looking at have an input
> impedance of 2K ohms. Can I get good results from using simple cable
> splitters, or do I need mic splitters with transformer isolation? I've
> sampled some specs, and a lot of boards seem to have an input impedance in
> the same general range as my pre's (1.3K to 3K). The isolation splitters
> are spendy, but if I need to use them to get clean recordings without
> messing with the signal to the FOH board I will. All advice is appreciated.
>
> Cheers,
> Walt
!