Large MB system (lengty post)

Design Concepts
1

Hello,

Let me introduce myself.  My name is Loren and I am currently a working at a mid to large sized recording facility in the US.  I must say that I am a huge fan of the site and I am a complete noob when it comes to this type of project.  I have been around computers and electronics all of my life (my dad built our first computer from a Heathkit kit).  Please interject if I have misunderstood something.  I apologize for the lengthy post but I believe the background will be helpful and have a few questions about an entire system I’m cooking up in my head.

Now the background on what led me to this site.  Part of my job is to make sure that the studio operates well. It’s a fairly new and I’m working on ensuring sessions go well.  One thing that I am working on is a system to allow producers to communicate with musicians through a variety of ways.  None of the rooms are physically attached to the control room, most of them are what some would call “stages” (we have 6 or 7 rooms of various size scattered throughout the building with connectivity to our control room).  On large sessions we might have 3 groups performing simultaneously (say a rhythm section, string orchestra, and chorus) with three or four producers working and each concentrating on one or two group’s performance.  On these types of sessions we will typically set up what is called a snoop microphone and a SLS (Studio Loud Speaker).  The snoop is setup on the maestro or the musician in charge, and the speakers of course allow the engineer talk with the group.  The problem comes for the producers; they do not have an elegant way of communicating with the group that they are focusing on. 

The system that I have come up to solve this problem would have three components.  The first would be a switch box with a microphone and headphone amp.  The switchbox would allow the producer to hear the mix coming off the console in their headphones (if they prefer headphones over the speakers).  More importantly it would also allow them between takes to pick which snoop(s) to listen to and if need be they could push a button to open their microphone to the speaker in the room.  The second unit would be the heart of the system and would provide the matrices for the microphones and speakers.  As well as all of the logic involved with routing the appropriate signal to the appropriate place (this is where Midi box comes into play).  The third unit would give the engineer control over levels from each mic to each speaker (if one producer is speaking loudly they could turn the mic down).

Here is the simple line drawing of how the Producers switchbox panel might look:

The three components would be connected via midi.  This would be the main “logicâ€.  Now to the “nuts and bolts†of the project.  The switches in the producer boxes would be connected to a DIn card.  The midi out would be connect to the midi in of the matrix box that would hopefully fire a Dout card that would then trigger an audio switch (very low noise) allowing the producers mic to be heard in the speakers of choice or allowing the producer to hear the snoop of choice.  The Engineer control box is the latest addition and I need a little more thought before I’ll have any “intelligent†questions.  So here are my questions thus far:

  1. Can one Core in the matrix box accept and deal with multiple midi channels or am I limited to a single channel per Core?

  2. From the reading I have done the Midibox64E seems like a good platform for the switchbox and matrix boxes, or am I making a selection mistake?

  3. It seems to me that a good idea might be to build a simple device to see if I have a basic understanding of the concept and then add to what I know.  For example making 2 boxes one with a DIn card loaded with a couple switches, the second with a DOut and some LEDs.  This would let me see if I can get the programming down (not my strong suit) and make sure that I have an idea of the fundamentals.  Does anyone have any thoughts?

  4. The biggest hurdle for me is Programming.  I have seen some Java interfaces that look quite simple which is great, my concern is if I have to do anything in C.  Does programming in C require a special app (please forgive my ignorance) or is it something that can be accomplished in a text editor?

I have really enjoyed the site and am very excited about this project.  Any input would be greatly appreciated! 

Thanks!

Loren

2
  1. Can one Core in the matrix box accept and deal with multiple midi channels or am I limited to a single channel per Core?

… yes, multible

  1. From the reading I have done the Midibox64E seems like a good platform for the switchbox and matrix boxes, or am I making a selection mistake?

… yes

  1. From the reading I have done the Midibox64E seems like a good platform for the switchbox and matrix boxes, or am I making a selection mistake?

… just clarify what you wanna do exactly, make some signal/logical flow charts, try to find out what MBHP-modules you need and if you don’t know how to continue, ask in the forum for help

  1. The biggest hurdle for me is Programming.   I have seen some Java interfaces that look quite simple which is great, my concern is if I have to do anything in C.  Does programming in C require a special app (please forgive my ignorance) or is it something that can be accomplished in a text editor?

… you can edit with a text editor bur you need a compiler (there are freeware compilers on the net to download)

Do you have an audio unit which you can control by MIDI? - You could use also a software based mixer.

The Engineer control box is the latest addition and I need a little more thought before I’ll have any “intelligent†questions

What you wanna do is like the typical monitoring and talkback control of an OnAir mixer. To get ideas, see page 19 (diagram) in this brochure.

http://www.studer.ch/pdf/brochures/(1)%20OnAir%203000Net%20(16-08-05)lr.pdf

Greets, Roger

3

Roger,

Thanks for the speedy reply.  It’s very helpful.

The Producer switch boxes would be fairly simple, A Core, a DIN card and some switches.  Possibly a circuit that would make the switch lamp blink if someone else is talking to the room, but again not very complex.  If I ended up implementing the blink circuit obviously the switchbox would need a DOUT.  More to come on the switchbox soon (I need to lookup the timer circuit and then draw the entire box).

Here is a quick drawing of a schematic for one microphone with one switch and level control to one room:

http://ljzimmer.fatcow.com/Talkback/One-channel-schematic.jpg

We will be using external Mic Pres for this.  The top left will be the input stage and unbalance.  Once it leaves the input stage it hits the ssm switch controlled by a DOut that is triggered by the Midi coming from the Producers switch box.  When it leaves it goes through another gain stage and then to a PGA2311.  This would be controlled by Midi from the Engineer box.

Do I have the Pinouts for the 2311 correct?  I have seen that a few other folks have gotten this chip to work but have not seen a schematic of it yet.  After the 2311 the audio is rebalanced and leaves the talkback system.

Keep in mind that for the input shown there would be an additional 8 outputs with the same components after the first gain stage.

I will work on drawings for the Producer and Engineer boxes next and will post them as I complete them.

Now to address some of the questions that have arisen from your reply.

1.  At what point do I know that I need a second core?

2.  I would assume that I enter C compiler into Google or go to download.com or something of that nature to get a compiler?

Again thanks for all of your help and interest,

Loren

Thanks again for your input,

Loren

4

Hello Everyone,

I wanted to bring all who had shown interest up to speed on how this project is coming.  I had posted last Thursday with the latest details and questions, but I think due to the server crash that the most recent posts are gone.  So here is where things stand as of now. 

I think that I have found a good source for learning C and C++.  Thanks to all for all of the info on what I will need.  I am sure that once I have the first core or two built that there will be more questions about programming this thing, but for now onto hardware issues.

I think that I am going to need to need multiple cores on the main matrix box because of the number of switches to control (128 from the producer’s boxes and possibly another 64 from the engineer’s box).  This leads me to my first question.  I am planning to install a USB module to act as the main interface with a computer.  My question is this:  Aside from the connection to the USB interface will there need to be any other physical connections to link the two cores?  I would assume that there would be (possibly MI and MO?).  I also assume that there would be some programming involved (I will continue to look for examples).

I have finished a couple of rough draft drawings and have started a website dedicated to this project.  It can be found at:

www.lorenzimmer.com/Talkback/Talkbackindex.htm

I have been thinking of having custom circuit boards made for all of the boxes and I am curious what others think about the idea.  Here is why I think that this might be a good idea (anyone is encouraged to tell me why they think I have fallen off the turnip truck).  For this system there are going to be two issues that are major hurdles.  The first is physical space.  I am pretty sure that there will be many components inside the box, any chance to simplify and combine several modules into one might be a good idea.  The second is to reduce the number of “jumper cables†and simplify the how many connections are required inside the box. 

Any thoughts?

Also the other day I received some PGA 2311 chips from Texas instruments.  I would like to start testing them soon but I am unsure of how to connect them.  I have compared the 2311 to the 595 and found that they both have the following:

CS

DI (the 2311 calls this SDI for serial data in I assume that it’s the same thing)

DO (Again the 2311 calls this SDO)

SCLK

So one would assume that since they are the same that those 4 pins would be connected the same way for both chips.  Yes, no?

Two things confuse me about the 2311 the first is the ZCEN pin (the tech document lists it as “Zero crossing Enable inputâ€.  Does anyone know what it does or if it’s important to this app?  The Second is a digital ground.  I also saw that on the main chip for the USB interface.  I’m sure that this is a fairly simple concept that I just haven’t run across yet but can someone explain the difference between an analog ground and a digital ground?

I know that there had been talk of some folks using the 2311 in their projects.  Does anyone have an example of a schematic and some programming?

The last question for now is do I need to be concerned about where I put some of these processing chips to avoid noise in my audio path?  Keep in mind that this will be used in a recording studio so quiet clean signals are a must!

Thanks to all for the support!

Loren

5

Food for thought: 8 ins and 8 outs is 64 switches, not 8…

6

Right, but where did my math go wrong?  I’m so buried in some of the details I’m not sure where I made my mistake.

Thanks,

L

7

Well you have to be able to switch it like this:

In  - Out

Ch1 - Ch1

Ch1 - Ch2

Ch1 - Ch3

Ch1 - Ch4

Ch1 - Ch5

Ch1 - Ch6

Ch1 - Ch7

Ch1 - Ch8

Ch2 - Ch1

Ch2 - Ch2

etc etc…

There are crosspoint switches available to do stuff like this though :slight_smile:

8

I see what your saying about the switching (and have implemented that into my drawings). 

There are crosspoint switches available to do stuff like this though

Do you know of a crosspoint switch that is used in audio consoles?  I know that such a thing exists for digital consoles because of all of the routing capabilities but have not seen such a thing for an analog application.

The reason I am going this way is that I have seen the ssm 2402 used in consoles and I know that it’s quiet and clean.  And to be perfectly honest this project started out much simpler (one mic to one speaker) and has grown so that we aren’t doing 20 versions of the box.  So any input on how to make the thing less complex would be greatly appreciated!  ;D

Thanks

Loren