Passive? routing? matrix? switcher with multiple busses?

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

"Loren Amelang" wrote ...
> Is there really no such thing as a passive matrix switcher with
> multiple internal busses, that can make multiple independent
> connections among any of its I/O connectors? Or have I just not found
> the proper search term?

The nature of video is such that routing a video source to a
variable number of destinations is not possible the way it
is in audio. Most modern audio sources are low-impedance
voltage sources and audio destinations are relatively high-
impedance sinks. This allows one to route an audio output
to several destinations without appreciable loss or distruption.

However, video signals have up to 5,000x more bandwidth
than audio and need properly-matched source and load impedances
to operate properly. A video routing switcher is actually a
combination of a matrix switch and several distribution amplifier
stages.

Note that video matrix switch ICs (some even completely self-
contained with output amps, etc.) are available from vendors
like Maxim, etc. See a listing of them at...
http://www.maxim-ic.com/solutions/ [...] p?pl_pk=50

See particularly MAX453, MAX454, MAX455 (2x1, 4x1,
and 8x1 buffered video multiplexers or the newer
MAX4359, MAX4360, MAX4456 (4x4, 8x4, and 8x8
buffered video crosspoint switch circuits.

Many of their ICs are available in an "Evaluation Kit" where
the chip is already installed on a PC board with all the required
peripheral components to make a working circuit.

I have made myself a couple of video Distribution Amplifiers
by using the Evaluation Kits with first-class performance and
specifications at a cost far less than anything you could buy off
the shelf. Of course I had to provide my own enclosure, connectors,
power supply, etc. so likely not practical for everyone.

Maxim not only makes cool ICs, but they also sell them direct
online (at www.maxim-ic.com) and many of them are available
at vendors like www.digikey.com, etc.

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

On Sat, 4 Dec 2004 14:12:40 -0800, "Richard Crowley"
<rcrowley7@xprt.net> wrote:

>"Loren Amelang" wrote ...
>> Is there really no such thing as a passive matrix switcher with
>> multiple internal busses, that can make multiple independent
>> connections among any of its I/O connectors? Or have I just not found
>> the proper search term?
>
>The nature of video is such that routing a video source to a
>variable number of destinations is not possible the way it
>is in audio. Most modern audio sources are low-impedance
>voltage sources and audio destinations are relatively high-
>impedance sinks. This allows one to route an audio output
>to several destinations without appreciable loss or distruption.

Understood. While I have occasionally connected a single source to two
destinations simultaneously with not totally disastrous results, my
main goal is to be able to make two (or more) simultaneous connections
between single sources and single destinations. The equivalent of the
"tape-monitor" loop in a receiver, for instance.

>However, video signals have up to 5,000x more bandwidth
>than audio and need properly-matched source and load impedances
>to operate properly. A video routing switcher is actually a
>combination of a matrix switch and several distribution amplifier
>stages.

Is that necessary if you are only connecting a single destination to
any one source? Assuming they are compatible when connected directly,
of course?

>Note that video matrix switch ICs (some even completely self-
>contained with output amps, etc.) are available from vendors
>like Maxim, etc. See a listing of them at...
>http://www.maxim-ic.com/solutions/crosspoint_switches/index.mvp?pl_pk=50
>
>See particularly MAX453, MAX454, MAX455 (2x1, 4x1,
>and 8x1 buffered video multiplexers or the newer
>MAX4359, MAX4360, MAX4456 (4x4, 8x4, and 8x8
>buffered video crosspoint switch circuits.

Interesting! I've used several Maxim chips in other projects, and
somehow I had a feeling I would end up building my own switcher.
Thanks!

Maybe "crosspoint switch" is the search term I was looking for?

Loren

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

"Loren Amelang" wrote ...
> "Richard Crowley" wrote:
>
>>"Loren Amelang" wrote ...
>>> Is there really no such thing as a passive matrix switcher with
>>> multiple internal busses, that can make multiple independent
>>> connections among any of its I/O connectors? Or have I just not found
>>> the proper search term?
>>
>>The nature of video is such that routing a video source to a
>>variable number of destinations is not possible the way it
>>is in audio. Most modern audio sources are low-impedance
>>voltage sources and audio destinations are relatively high-
>>impedance sinks. This allows one to route an audio output
>>to several destinations without appreciable loss or distruption.
>
> Understood. While I have occasionally connected a single source to two
> destinations simultaneously with not totally disastrous results,

Professional/industrial video equipment usually has high-impedance
inputs with two connectors so that you can "loop-through" the video
signal to additional inputs. Then you put a 75-ohm termination at the
end of the line.

But few (if any?) consumer devices have loop-through inputs.
Connecting a standard 75-ohm ouput to more than one 75-ohm
terminated inputs will significantly degrade the signal, even
reducing the amplitude of the sync portion to the point where
some equipment won't be able to lock to it. NOT RECOMMENDED!

> my main goal is to be able to make two (or more) simultaneous
> connections between single sources and single destinations.
> The equivalent of the "tape-monitor" loop in a receiver, for instance.

In that case, Scott's suggestion of a patch bay may be more like
what you are looking for. I was assuming you were actually
needing an any-to-any solution which would call for a non-
blocking matrix.


>>However, video signals have up to 5,000x more bandwidth
>>than audio and need properly-matched source and load impedances
>>to operate properly. A video routing switcher is actually a
>>combination of a matrix switch and several distribution amplifier
>>stages.
>
> Is that necessary if you are only connecting a single destination to
> any one source? Assuming they are compatible when connected directly,
> of course?

Yes. A properly driven and terminated transmission line is
required for high-quality transport of any high-frequency signal
like video.

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

In article <10r7kreoa6v397d@corp.supernews.com> rcrowley7@xprt.net writes:

> > Radio Shack has had a few variations on that.

> That would be a great suggestion if he were looking for audio-
> only. But I understood that he was asking for audio & video.

He may need to buy two devices, or spend more than he was expecting to
get one device that switches both video and stereo audio in one shot -
a "matrix" for sure.

How much is not having to use both hands worth?

--
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,rec.video.production (More info?)

I agree. The lowest cost "real solution" would be to use a small DA for
each source, and a patch bay to send them to their destinations. This is
essentially what a router is, just in one case and with a control
mechanism - - either serial or with a dedicated panel.

If real broadcast quality isn't important, then check out some vendors
associated with the security field. I'm often surprised by the low prices
in the couple of catalogs I happen to get.

Steve



"Mike Rivers" <mrivers@d-and-d.com> wrote in message
news:znr1102335580k@trad...
>
> In article <10r7kreoa6v397d@corp.supernews.com> rcrowley7@xprt.net writes:
>
> > > Radio Shack has had a few variations on that.
>
> > That would be a great suggestion if he were looking for audio-
> > only. But I understood that he was asking for audio & video.
>
> He may need to buy two devices, or spend more than he was expecting to
> get one device that switches both video and stereo audio in one shot -
> a "matrix" for sure.
>
> How much is not having to use both hands worth?
>
> --
> 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?)

Found a definition of "matrix switcher":

<http://www.extron.com/product/prodtype03.asp>
"Matrix switchers route multiple audio/video sources to multiple
audio/video destinations. Matrix switchers provide the ability to
route any input to any output - or multiple outputs - at any time."

I guess they mean a _buffered_ matrix switcher can route one input to
multiple outputs.


It looks like the key to my terminology question is that when a
switcher offers more than "n by 1" switching, it can specify the
number of available crosspoints. As in:
"Kramer VS-44AV 4x4 (4 Crosspoint) Mechanical CV / Audio Matrix, 220
MHz"

<http://www.kramerelectronics.com/indexes/desc.asp?p=VS-44AV>
"The Kramer VS-44AV is a high quality mechanical 4x1x4 switcher for
composite video and stereo audio signals. It is designed to route up
to four sources to any one of four available outputs simultaneously.
The VS-44AV is unique in allowing four different cross points of video
and stereo audio to operate at the same time. However, it is important
to note that it cannot distribute an input signal to multiple outputs
simultaneously."

I assume the limitation on "an input signal to multiple outputs
simultaneously" is because it isn't buffered.

I'm still not clear what the "4x1x4" terminology means. It sounds like
a combination of a 4x1 input switch and a 1x4 output switch, but that
would only allow four simultaneous crosspoints if they were all in the
same row or column. I want to be able to put four simultaneous
crosspoints in a diagonal or random pattern. So maybe this still
doesn't do what I imagined. They don't make a passive counterpart for
S-Video, anyway.


Another useful search term is "loop back" (as in the "tape-monitor"
facility of a receiver).

<http://www.extron.com/technology/faq.asp>
"Video loop back is a feature of Extron system switchers that allows
selected inputs to be looped out of the system switcher to a scaler or
scan converter and then looped back into the System. The result is the
switcher and the scaler or scan converter essentially operate as one
unit."

That would solve one of my problems, but I really want to be able to
switch any appropriate piece of equipment into the loopback position.
That patchbay is sounding better all the time. Especially since I
can't always use "audio follows video" switching. Sometimes the audio
goes to or through additional equipment.

Loren

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

"Mike Rivers" <mrivers@d-and-d.com> wrote in message
news:znr1102369850k@trad...
>
> In article <rgi9r016rc5hvndq74mqauv4ckf0bbahua@4ax.com> loren@pacific.net
> writes:
>
>> >Radio Shack model 42-2115
>
>> Thanks! Looks like a handy gadget to have around. Not sure I'll be
>> using it with my serious audio system, though... Have to look inside
>> first, at least.
>
> You know what they say about laws and sausages - If you like them,
> you'd better not watch either being made. Just cheap switches and some
> resistors.

Are you describing the laws or the rat-shack switch boxes? :-)