[semi-OT] midi snakes using CAT5?

[Jörn Nettingsmeier-6]

hi everyone!


i'm playing with my shiny new BCF2K, and i'm going to use it some
distance from my machine, so i'm going to try a midi link instead of USB.

what is the maximum length of midi chain that you have used without
problems? i read somewhere that no more than 15 meters are recommended,
which strikes me as pretty short even if it's unbalanced.

my idea is to abuse a cat5 cable as a triple midi loom - do you think
that could work? pinout would be as follows:

1 midi 1 signal
2 midi 1 ground
3 midi 2 signal
4 midi 2 ground
5 midi 3 signal
6 midi 6 ground
7 common +5V
8 common +5V


best,

jörn



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[laseray]

On November 1, 2009 10:47:44 am Jörn Nettingsmeier wrote:

> hi everyone!
>
>
> i'm playing with my shiny new BCF2K, and i'm going to use it some
> distance from my machine, so i'm going to try a midi link instead of USB.
>
> what is the maximum length of midi chain that you have used without
> problems? i read somewhere that no more than 15 meters are recommended,
> which strikes me as pretty short even if it's unbalanced.
>
>
> my idea is to abuse a cat5 cable as a triple midi loom - do you think
> that could work? pinout would be as follows:

15 meters is a recommendation based on typical cables used in a simple system.
Data corruption ensues somewhere after 15m, depending on cable quality, EMI,
and so forth. I would imagine a CAT5 as having better shielding and IIRC runs
for that are advised to somewhere up to 50m. Different frequency ranges though,
so signal loss/degradation per meter may vary.

Usually you need a buffer/booster box for any regular MIDI cable runs greater
than 15m.

You can also use professional microphone cables for MIDI with DIN plugs. That
might get you a little better EMI rejection and hence a longer run also.

A CAT5 cable should work, as long as the pairs of signal/grounds are really
twisted together. Hum and crosstalk may be a factor otherwise.

Raymond

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On Sun, 2009-11-01 at 12:56 -0400, Raymond Martin wrote:
>
> 15 meters is a recommendation based on typical cables used in a simple system.
> Data corruption ensues somewhere after 15m, depending on cable quality, EMI,
> and so forth. I would imagine a CAT5 as having better shielding and IIRC runs
> for that are advised to somewhere up to 50m. Different frequency ranges though,
> so signal loss/degradation per meter may vary.

My recollection is that when MIDI was originally standardised, they
needed to specify a maximum length, and that 15M was chosen somewhat
arbitrarily (No tests were done, no eye patterns examined).

Now midi is actually at heart a 5mA current loop interface running at a
fairly low baud rate (31.25 Kbaud IIRC), so should be good for far more
then 15m without any problem, however nobody really knows and it will
depend a bit on the environment and the receiver.

Interference is unlikely to be an issue assuming good quality twisted
pair cable (Cat 5 counts), but bulk capacitance just might ultimately
limit the length.

Regards, Dan.

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[Arnold Krille-3]

Hi,

On Sunday 01 November 2009 16:47:44 Jörn Nettingsmeier wrote:

> i'm playing with my shiny new BCF2K, and i'm going to use it some
> distance from my machine, so i'm going to try a midi link instead of USB.
> what is the maximum length of midi chain that you have used without
> problems? i read somewhere that no more than 15 meters are recommended,
> which strikes me as pretty short even if it's unbalanced.
> my idea is to abuse a cat5 cable as a triple midi loom - do you think
> that could work? pinout would be as follows:
> 1 midi 1 signal
> 2 midi 1 ground
> 3 midi 2 signal
> 4 midi 2 ground
> 5 midi 3 signal
> 6 midi 6 ground
> 7 common +5V
> 8 common +5V

If you want to make use of the drilling of the pins in cat5, it should be

1+2 Midi 1
3+6 Midi 2
4+5 Midi 3
7+8 Midi 4

Why do you want to carry 5V? According to my docs, Midi is just Signal+ and
Signal- and shield. Which, when carried over Cat5, should be all on the
shield.

I made myself some adaptors Midi->XLR->Midi a year ago but never actually used
them to date.

Have fun,

Arnold


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[laseray]

On November 1, 2009 12:55:44 pm you wrote:

> On Sun, 2009-11-01 at 12:56 -0400, Raymond Martin wrote:
> > 15 meters is a recommendation based on typical cables used in a simple
> > system. Data corruption ensues somewhere after 15m, depending on cable
> > quality, EMI, and so forth. I would imagine a CAT5 as having better
> > shielding and IIRC runs for that are advised to somewhere up to 50m.
> > Different frequency ranges though, so signal loss/degradation per meter
> > may vary.
>
> My recollection is that when MIDI was originally standardised, they
> needed to specify a maximum length, and that 15M was chosen somewhat
> arbitrarily (No tests were done, no eye patterns examined).
>
> Now midi is actually at heart a 5mA current loop interface running at a
> fairly low baud rate (31.25 Kbaud IIRC), so should be good for far more
> then 15m without any problem, however nobody really knows and it will
> depend a bit on the environment and the receiver.
>
> Interference is unlikely to be an issue assuming good quality twisted
> pair cable (Cat 5 counts), but bulk capacitance just might ultimately
> limit the length.
>

Check MIDI manufacturers association pages, specifically:
http://www.midi.org/aboutmidi/tut_midicables.php

At the bottom it talks abut MIDI over Ethernet, with links.

Cheers,

Raymond
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[Jörn Nettingsmeier-6]

Arnold Krille wrote:

> Hi,
>
> On Sunday 01 November 2009 16:47:44 Jörn Nettingsmeier wrote:
>> i'm playing with my shiny new BCF2K, and i'm going to use it some
>> distance from my machine, so i'm going to try a midi link instead of USB.
>> what is the maximum length of midi chain that you have used without
>> problems? i read somewhere that no more than 15 meters are recommended,
>> which strikes me as pretty short even if it's unbalanced.
>> my idea is to abuse a cat5 cable as a triple midi loom - do you think
>> that could work? pinout would be as follows:
>> 1 midi 1 signal
>> 2 midi 1 ground
>> 3 midi 2 signal
>> 4 midi 2 ground
>> 5 midi 3 signal
>> 6 midi 6 ground
>> 7 common +5V
>> 8 common +5V
>
> If you want to make use of the drilling of the pins in cat5, it should be
>
> 1+2 Midi 1
> 3+6 Midi 2
> 4+5 Midi 3
> 7+8 Midi 4

sure, i just numbered the wires, your count is based on rj45, but i
meant the same.

> Why do you want to carry 5V? According to my docs, Midi is just Signal+ and
> Signal- and shield. Which, when carried over Cat5, should be all on the
> shield.

any midi has to carry 5v iirc. and midi is not balanced, so there is no
signal+ and signal-. would be cool if there was - then 100m would be no
problem :)


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[Arnold Krille-3]

On Sunday 01 November 2009 19:23:27 you wrote:
> Arnold Krille wrote:
> > Why do you want to carry 5V? According to my docs, Midi is just Signal+
> > and Signal- and shield. Which, when carried over Cat5, should be all on
> > the shield.
> any midi has to carry 5v iirc. and midi is not balanced, so there is no
> signal+ and signal-. would be cool if there was - then 100m would be no
> problem :)

Actually midi seems to be something that drives an led inside the opto-
coupler. So it doesn't matter if that signal is 5V to ground or 2.5V to -2.5V.
As long as the two "signals" are not connected to anything besides the opto-
coupler in the receiving device, all is well.
The book on my desk with electronic-nifties for studios labels the two pins
used by midi as signal+ and signal-...

Have fun,

Arnold


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[Fons Adriaensen-2]

On Sun, Nov 01, 2009 at 07:23:27PM +0100, Jörn Nettingsmeier wrote:

> any midi has to carry 5v iirc. and midi is not balanced, so there is no
> signal+ and signal-. would be cool if there was - then 100m would be no
> problem :)

Midi does not carry a 5V supply. You need 5V to (or more) to
create a midi output, but that voltage is required in the
equipment providing the output only.

A midi input is floating (the input of an optocoupler).

Pin 4 is the '+' side, pin 5 is '-'. Usually one of the
two has a series resistor (220R or so) to limit the current
if accidentally connected to a low-impedance voltage source,
and there may be a diode parallel to the optocoupler to
protect against reversed voltage.

For output, pin 4 is normally connected via a 220R
series resistor to +5V, and pin 5 is the output of an
open-collector logic gate able to sink at least 10 mA,
again with 220R in series. That is the standard way to
make a midi out. But since the input is floating you
could reverse the active/passive parts, e.g. use an
active high open collector output on pin 4 and connect
pin 5 to ground (both again via 220R). You could even
make it active in both states and balanced. But little
is gained by doing that. Some midi receivers may rely
on the 'standard' way to steal some power, but I don't
think the standard provides for this.

Ciao,

--
FA

Io lo dico sempre: l'Italia è troppo stretta e lunga.

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[David-712]

On Mon, Nov 2, 2009 at 4:55 AM, Dan Mills <dmills@...> wrote:

> On Sun, 2009-11-01 at 12:56 -0400, Raymond Martin wrote:
>>
>> 15 meters is a recommendation based on typical cables used in a simple system.
>> Data corruption ensues somewhere after 15m, depending on cable quality, EMI,
>> and so forth. I would imagine a CAT5 as having better shielding and IIRC runs
>> for that are advised to somewhere up to 50m. Different frequency ranges though,
>> so signal loss/degradation per meter may vary.
>
> My recollection is that when MIDI was originally standardised, they
> needed to specify a maximum length, and that 15M was chosen somewhat
> arbitrarily (No tests were done, no eye patterns examined).
>
> Now midi is actually at heart a 5mA current loop interface running at a
> fairly low baud rate (31.25 Kbaud IIRC), so should be good for far more
> then 15m without any problem, however nobody really knows and it will
> depend a bit on the environment and the receiver.
>
> Interference is unlikely to be an issue assuming good quality twisted
> pair cable (Cat 5 counts), but bulk capacitance just might ultimately
> limit the length.

My I offer some more information to clarify the notions of cable
"quality" and signal "loss/degradation".

Aside from the EMI issue, what limits performance here is not so much
cable "quality" whatever that means but the unavoidable physical
characteristics of the cable as a transmission line once its length
causes a time delay that is significant relative to the rise/fall
times of the signals it is carrying.

The speed of electromagnetic propagation is fast, but it is not
infinite. It takes time for a signal to travel from one end of the
cable to the other. Plus, if the termination impedance is not matched
to the cable impedance, then reflections will occur at either end of
the cable causing unexpected signal variations. Good old physics
screws up the imaginary fantasy of perfect 1's and 0's.

A good reference on this is www.national.com/an/AN/AN-808.pdf
particularly Figure 7 which is instructive even if you read none of
the text but just look at the picture.

The MIDI 1.0 spec keeps the cable length short to avoid addressing
these issues. It makes no attempt to specify terminating impedances
matched to cable impedance, or deal with any other long cable issues.

Another thing about the that MIDI spec is where it says "optoisolators
... rise and fall times should be less than 2 microseconds" which is
amusing because the total time of one midi bit is 3.2 microseconds. So
don't imagine you have nice square bits driving the system even if
your cable is zero length. So your optoisolators *might* be a limiting
factor depending on their speed (ie age, cost).

The transmitting equipment's ability to adequately drive
current/voltage into the cable impedance *might* be another limiting
factor.

This is not intended to put you off. If you get yourself an
oscilloscope and do some eye pattern tests (Fig 13 and Fig 15), you
might discover your equipment and chosen cable works fine at the
lengths you need. But this is the only way to know for sure.

If you do decide to do this, you would need to keep in mind that your
cable is terminated by a nonlinear impedance (the led in the receiver
optocoupler) so that adds an extra complication because voltage is not
proportional to current at that point in the system. You might need to
scope the output (ie not the input) of the receiver optocoupler for
errors.

So that is why the MIDI spec says to keep the cables short. It avoids
all these complicated issues, allows simple cheap circuitry and any
cheap cable with unspecified characteristic impedance, and yet was
fast enough for the audible performance latency requirement.

By the way, the reason Cat5 cable gives better performance in *other*
situations is because it has a defined characteristic impedance (100
ohms), and being known it can be matched in the design of the
transmit/receive device impedances to minimise reflections. Cat5 cable
does *not* provide that benefit when used to interconnect MIDI
devices, because they are not designed for 100 ohm cable.

Other relevant references are:
http://en.wikipedia.org/wiki/Transmission_line
http://en.wikipedia.org/wiki/Twisted_pair
http://en.wikipedia.org/wiki/Category_5_cable

And yes there is no need to run 5V down a MIDI cable. It is a current loop.

David
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[Gene Heskett]

On Sunday 01 November 2009, Arnold Krille wrote:

>Hi,
>
>On Sunday 01 November 2009 16:47:44 Jörn Nettingsmeier wrote:
>> i'm playing with my shiny new BCF2K, and i'm going to use it some
>> distance from my machine, so i'm going to try a midi link instead of USB.
>> what is the maximum length of midi chain that you have used without
>> problems? i read somewhere that no more than 15 meters are recommended,
>> which strikes me as pretty short even if it's unbalanced.
>> my idea is to abuse a cat5 cable as a triple midi loom - do you think
>> that could work? pinout would be as follows:
>> 1 midi 1 signal
>> 2 midi 1 ground
>> 3 midi 2 signal
>> 4 midi 2 ground
>> 5 midi 3 signal
>> 6 midi 6 ground
>> 7 common +5V
>> 8 common +5V
>
>If you want to make use of the drilling of the pins in cat5, it should be
>
>1+2 Midi 1
>3+6 Midi 2
>4+5 Midi 3
>7+8 Midi 4
>
>Why do you want to carry 5V? According to my docs, Midi is just Signal+ and
>Signal- and shield. Which, when carried over Cat5, should be all on the
>shield.

Except that I have yet to see a piece of cat5 with shielding.

>I made myself some adaptors Midi->XLR->Midi a year ago but never actually
> used them to date.
>
>Have fun,
>
>Arnold
>


--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
The NRA is offering FREE Associate memberships to anyone who wants them.
<https://www.nrahq.org/nrabonus/accept-membership.asp>

"I will make no bargains with terrorist hardware."
-- Peter da Silva
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[Gene Heskett]

On Sunday 01 November 2009, Jörn Nettingsmeier wrote:

>Arnold Krille wrote:
>> Hi,
>>
>> On Sunday 01 November 2009 16:47:44 Jörn Nettingsmeier wrote:
>>> i'm playing with my shiny new BCF2K, and i'm going to use it some
>>> distance from my machine, so i'm going to try a midi link instead of
>>> USB. what is the maximum length of midi chain that you have used without
>>> problems? i read somewhere that no more than 15 meters are recommended,
>>> which strikes me as pretty short even if it's unbalanced.
>>> my idea is to abuse a cat5 cable as a triple midi loom - do you think
>>> that could work? pinout would be as follows:
>>> 1 midi 1 signal
>>> 2 midi 1 ground
>>> 3 midi 2 signal
>>> 4 midi 2 ground
>>> 5 midi 3 signal
>>> 6 midi 6 ground
>>> 7 common +5V
>>> 8 common +5V
>>
>> If you want to make use of the drilling of the pins in cat5, it should be
>>
>> 1+2 Midi 1
>> 3+6 Midi 2
>> 4+5 Midi 3
>> 7+8 Midi 4
>
>sure, i just numbered the wires, your count is based on rj45, but i
>meant the same.
>
>> Why do you want to carry 5V? According to my docs, Midi is just Signal+
>> and Signal- and shield. Which, when carried over Cat5, should be all on
>> the shield.
>
>any midi has to carry 5v iirc. and midi is not balanced, so there is no
>signal+ and signal-. would be cool if there was - then 100m would be no
>problem :)

Preface, I am a C.E.T., and a broadcast engineer with 47 years time in the
field.  Yeah, that and my 75 years age makes me an old fart. ;-)

Midi, by spec, is a current source, just enough to run the opto-isolator in
the next piece of gear.  The rise and fall times become degraded by cable
capacitance, eventually leading to timing errors.  AFAIK, no one has actually
tried to run it using a low capacitance cable to extend the range.  In cat5,
the twisted pair is probably only a slightly higher impedance than the
microphone cables I have bought labeled as very expensive midi cable just
because they had the right connectors on the end.  So it might go a little
further than the store bought cables, but not by very much.

Another effect in the 4 twisted pair cat5 is crosstalk if using each pair as
a different midi port, but I don't think that would show up before the signal
lags ate the signals lunch.

Just for grins, I once changed the crystal in an rs232 interface so that it
could be run at midi speeds, then hooked it up to a couple of different
keyboards.  The polarity inherent in the opto-isolator inputs seemed to
protect the input and I ran it that way for a couple years with no damages to
either keyboard, or to the rs-232 ports hardware.

From an engineering standpoint, midi, designed as an idiot proof interface,
has served us very well indeed.  But with cat5 all over the place and cheap
as dirt, I am amazed that the gear makers haven't switched interfaces. Today,
the average midi circuit is badly overloaded because its so slow. I've heard
music that because of the note update rate, sounded like Floyd Cramer's
piano, and it wasn't written that way...  Gigahertz ethernet can be run
several hundred feet, with 200-2000x the data rate midi can manage.  Think of
the possibilities that could open up.  Every instrument in a 200 piece
orchestral construction getting its note on in the same millisecond.  That
might be too perfect, too mechanical, but you get the idea.

--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
The NRA is offering FREE Associate memberships to anyone who wants them.
<https://www.nrahq.org/nrabonus/accept-membership.asp>

"I will make no bargains with terrorist hardware."
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On Mon, 2009-11-02 at 10:52 +1100, David wrote:

> Another thing about the that MIDI spec is where it says "optoisolators
> ... rise and fall times should be less than 2 microseconds" which is
> amusing because the total time of one midi bit is 3.2 microseconds. So
> don't imagine you have nice square bits driving the system even if
> your cable is zero length. So your optoisolators *might* be a limiting
> factor depending on their speed (ie age, cost).

I think you make a factor of 10 error! One midi bit is 1/31250 = 32
microseconds, not 3.2 which makes a difference.

On transmission line effects, lets see, 31,250 baud lets say you need
the first ten harmonics to give a reasonable eye pattern, so say 300Khz
bandwidth, and that transmission line effects become important at one
tenth of a wavelength (reasonable rule of thumb), and that velocity of
propagation is 0.6C, then:

Wavelength = 300,000,000*.6/300,000 = ~600M, so transmission line
effects can be totally ignored out to at least 60M or so.

Lumped constant models look to be quite good enough, and it will almost
certainly be a 5mA sources ability to charge the cable capacitance that
will impose the ultimate limit.

Current loops tend to have excellent interference rejection, and the
fairly tight twisting in cat 5 can only help with this.    

Regards, Dan.

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[David-712]

On Mon, Nov 2, 2009 at 12:20 PM, Dan Mills <dmills@...> wrote:

> On Mon, 2009-11-02 at 10:52 +1100, David wrote:
>
>> Another thing about the that MIDI spec is where it says "optoisolators
>> ... rise and fall times should be less than 2 microseconds" which is
>> amusing because the total time of one midi bit is 3.2 microseconds. So
>> don't imagine you have nice square bits driving the system even if
>> your cable is zero length. So your optoisolators *might* be a limiting
>> factor depending on their speed (ie age, cost).
>
> I think you make a factor of 10 error! One midi bit is 1/31250 = 32
> microseconds, not 3.2 which makes a difference.

Yes you are correct, I made a factor of 10 error.

The copy of the MIDI 1.0 spec I looked at says "the interface operates
at 31.25 kbaud" so I interpreted this as 31.25 10-bit symbols per
second, which is one possible interpretation of baud, but this is not
what they meant. The slippery old baud claims another victim. They
meant "the interface operates at 31.25 kbit/s", so I made a mistake
and thank you for clearing it up !!

I broadly agree with your rule of thumb, and it is a useful addition
to my attempt to give a better understanding of what issues are
involved here, and it makes sense to add it.

But nothing beats a test once you know what all the issues are, which
was the point I was attempting to make.

Also it would probably not hurt to improve the midi output's EMI
rejection with some ferrite beads and bypass caps if there's going to
be a longwire antenna hanging off it, even if it is made of twisted
pair.

Cheers
David
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[Arnold Krille-3]

On Monday 02 November 2009 00:56:15 Gene Heskett wrote:

> On Sunday 01 November 2009, Arnold Krille wrote:
> >If you want to make use of the drilling of the pins in cat5, it should be
> >1+2 Midi 1
> >3+6 Midi 2
> >4+5 Midi 3
> >7+8 Midi 4
> >Why do you want to carry 5V? According to my docs, Midi is just Signal+
> > and Signal- and shield. Which, when carried over Cat5, should be all on
> > the shield.
> Except that I have yet to see a piece of cat5 with shielding.

Look for that STP or S/UTP or FTP cables :-)

Honestly all the cables I make myself are from (single-)shielded twisted pair.
And except for the cheap cables that come with some devices, all the cables I
buy are shielded too (with no extra costs).

Unshielded is usable to connect that slow wlan-repeater that can't really go
more then 10MBits but for anything else in networking you should used shielded
cable.

And as Jörn is asking about using it in professional surroundings, it will
most definitely be the shielded cable he is using...

Have fun,

Arnold


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[Gene Heskett]

On Monday 02 November 2009, Arnold Krille wrote:

>On Monday 02 November 2009 00:56:15 Gene Heskett wrote:
>> On Sunday 01 November 2009, Arnold Krille wrote:
>> >If you want to make use of the drilling of the pins in cat5, it should
>> > be 1+2 Midi 1
>> >3+6 Midi 2
>> >4+5 Midi 3
>> >7+8 Midi 4
>> >Why do you want to carry 5V? According to my docs, Midi is just Signal+
>> > and Signal- and shield. Which, when carried over Cat5, should be all on
>> > the shield.
>>
>> Except that I have yet to see a piece of cat5 with shielding.
>
>Look for that STP or S/UTP or FTP cables :-)
>
>Honestly all the cables I make myself are from (single-)shielded twisted
> pair. And except for the cheap cables that come with some devices, all the
> cables I buy are shielded too (with no extra costs).
>
>Unshielded is usable to connect that slow wlan-repeater that can't really
> go more then 10MBits but for anything else in networking you should used
> shielded cable.
>
>And as Jörn is asking about using it in professional surroundings, it will
>most definitely be the shielded cable he is using...
>
>Have fun,
>
>Arnold
>

FWIW, I have around 120 feet of unshielded cat5 stretched around my property,
with 100mbit cards at all points, from a switch I can see here in my den,
down into the basement and out through the same hole the telco cable comes
in, under the back porch floor, and up the house wall to an anchor point on
the porch roof, thence to an anchor point at the peak of a workshop shed I
built 10 years ago, down to a 4 port switch in there, then from that another
cable is currently running out the shop door and about 35 feet across the
back yard to a window in the garage, and 20 some feet to a test machine.  I
can move something from here to that last machine at 10megabytes/second.  
Std, unshielded cat5.    The piece from the house to the shed has been
swinging in the wind for about 6 years now, a never ending source of
amazement to me that it hasn't failed.

My point is that the opto-isolation isn't required for ethernet since it is a
transformer coupled differential circuit, therefore quite immune to
longitudinal voltages caused by poor wiring practices, local high powered AM
broadcasting signals etc.

--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
The NRA is offering FREE Associate memberships to anyone who wants them.
<https://www.nrahq.org/nrabonus/accept-membership.asp>

If this is timesharing, give me my share right now.
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[Jens M Andreasen-2]

Slightly related: I am probably not the only person who gets cell-phone
signals leaking in all over the place, right?
 
* Says beep-be-deep in speakers.
* Moves mouse-pointer around.
* Shakes CRT pictures back and forth.

The nastiest thyristor-dimmers might be gone by now, but modern
cell-phones aren't too much fun either.

But useful for testing quality of cables and shielding perhaps?

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