MIDIBox Mixer - A PGAx311 Audio Mixer

[strophlex]

I don't know if anybody has some pcbs. I did some layout and have 2 protos lying around. bUT i didnt had the time to test them. And I dont want to publish non working pcbs ;P

greetz

I have read through the thead now and realize the status of project. I'll follow this thread and see what comes out of it.

[strophlex]

I got an idea. Would it be possible to attach a mb-mixer to an excisting mb-lc for a complete analog audio mixer that can remote control / be remote controled via midi? Are there some obvious limitations that makes this impossible? I understand that the software of the two projects has to be merged in some way and that the memmory of the 18f452 might not be sufficient, but i guess upgrading the pic should remedy that issue.

[dj3nk]

Good idea, but I think its better just to add motorfader (aout) function to the mb mixer application. I don't think a "merge" of the projects is so easily possible.

With aouts you could even add more real controls like eqs to your mixer. Midifying analog gear is an actual discussion here. Go and look at the wiki. There are some hints about the possibilities. But this wasnt worker out deeper by anyone as far as I know.

greetz

[lylehaze]

I have not yet merged the mixer software with anything except MB-Stor. Since the mixer uses J10, there should be no conflict with the MotorFader modules. writing to the mix array does require disabling DIN/DOUT scans for a few ms though. That's really the only compromise I can think of right now.

MB-Stor does require J6 and J7, so it cannot be used with Motorfaders. But that's another project.

I have not posted the board designs to try and prevent seeing my mixer for sale on E-Bay.

If anyone is interested in boards, please express your interest to SmashTV. If he hears from enough people, he might decide to carry the boards in his webshop.

If that doesn't work out, I will need to find someone who wants to organize a bulk order. I can't. I'm broke and unemployed.

Thanks for your interest (Yes, the mixer sounds great, I'm listening to it now).

Any interest in a MIDI controlled MP3 player? I installed one of those in the mixer last week. It comes with a 8 Gig bankstick :-)

LyleHaze

[dj3nk]

If Smash or nobody else has the time to do that I'd spend the time for arranging a bulk order for these pcbs.

This project is really really great. When I am closing my eyes I am seeing a biiiiiiiiig mixer combined from LC's, 64's and this project. ;D

Axels monster lc needs some new analog channel strips soon :D

EDIT: What is Mb Stor ? oO

[lylehaze]

I really need to start a new thread.

MB stor is a new project. I added it to my mixer, but it can be separate. It's really simple, and the hardware is already built. See http://www.vinculum.com/prd_vmusic1.html

It is:

an MP3 player, a .wav player, and it plays format 0 midi files too, with it's own internal voices.

It also handles the filesystem of a USB stick. Programs can open files for reading or writing. The filesystem is very much like a DOS command line. (CD, DIR, MD etc).

Right now it plugs into J6 and J7, so no motorfaders and no multiplexed AIns available. The current state of the software just passes all commands in and out by SysEx messages, so I can experiment from a command line.

Once I get time, I'll probably write a MIDI file player that plays the file to the MIDIBox MIDI out, I will then release it all. Right now all my code is in ASM. I'm hoping to re-write most of it in C and release it as a proper module. This will take some time.

It's a fun toy.

LyleHaze

[dj3nk]

I've started a topic to collect the interests in this pcbs. It's located here:

http://www.midibox.org/forum/index.php/topic,12195.html

greetz

[lylehaze]

strophlex:

from the "Project purpose and intent"

One of the best things about this new mixer is that there is no control surface. I have found it incredibly better to keep the C.S. separate. By separating them, you can put the audio "backend" at the stage, where the signals are created and the amplifiers are fed. You can move the controls to the other end of a MIDI cable. You have just eliminated dozens of shielded audio cables running from the stage all the way up to the mix booth. All the audio stays backstage where it belongs. Even better is for a studio environment. I have my control surface and my MBMixer plugged in to separate MIDI ports on my computer. They are patched together in software. So I always have full manual control, but I can also record a "dynamic" mix with a sequencer, and play it back as easily as any other MIDI track. I also have an on screen mixer that is fully functional, and a few hotkeys on my PC keyboard that my wife requested for muting the system. (or turning it WAY FREAKING UP!)

To answer your question: You might be able to put an LC and a MBMixer on the same core, but you would get better results if you make them separately. But you are right, you really need a good C.S. to have fun with the mixer.

LyleHaze

[strophlex]

strophlex:

from the "Project purpose and intent"

One of the best things about this new mixer is that there is no control surface. I have found it incredibly better to keep the C.S. separate. By separating them, you can put the audio "backend" at the stage, where the signals are created and the amplifiers are fed. You can move the controls to the other end of a MIDI cable. You have just eliminated dozens of shielded audio cables running from the stage all the way up to the mix booth. All the audio stays backstage where it belongs. Even better is for a studio environment. I have my control surface and my MBMixer plugged in to separate MIDI ports on my computer. They are patched together in software. So I always have full manual control, but I can also record a "dynamic" mix with a sequencer, and play it back as easily as any other MIDI track. I also have an on screen mixer that is fully functional, and a few hotkeys on my PC keyboard that my wife requested for muting the system. (or turning it WAY FREAKING UP!)

To answer your question: You might be able to put an LC and a MBMixer on the same core, but you would get better results if you make them separately. But you are right, you really need a good C.S. to have fun with the mixer.

LyleHaze

You are so right! I will just build the two projects separately. When my 5x5 gm5 module is finnished i will have plenty of ins and outs anyway :)

[matoz]

Euh... uhm...  ???

I added my name in mbmixer pcb bulk order on the Wiki, and i' ve just read the topic here : http://www.midibox.org/forum/index.php?topic=12195.0 

Mbmixer is a very good and usefull project, will the pcb bulk order continue? or will be have another bulk order?

Best regards

[strophlex]

Euh... uhm...   ???

I added my name in mbmixer pcb bulk order on the Wiki, and i' ve just read the topic here : http://www.midibox.org/forum/index.php?topic=12195.0   

Mbmixer is a very good and usefull project, will the pcb bulk order continue? or will be have another bulk order?

Best regards

I have provided the board files to SmashTV. Once he has a chance to get some made, they will be available through his webshop. He is working out sources to some of the unusual parts now.

I really appreciate the offer to manage a group buy, but I think the webshop is more convenient for most people.

So, eventually you will be able to buy the pcbs from Smash TV's store.

[matoz]

Ok, so, i will wait they appear on smashtv shop.

thanks  ;)

[matoz]

i' ve read another time wiki mb mixer, and i have questions about limits:

I' ve understand we are limited by 16 midi channel.

One board have 4in to 4out so is it  possible to use it as 1 stereo input and 1 stereo output and 2 mono fx out? if yes, if i use 16 board like that, i have 16 stereo channel and 2 fx send...

And is it  possible to use it as 2 mono input and 1 stereo output and 2 mono fx out? if yes, if i use 8 board like that, i have 16 mono channel with 2 fx send...

My needs are 9 stereo input and 7 mono input with 2 fx send (if it is possible  ;-) so it do 16 channels.

So i could use 9 board as "1 stereo in/2monofx" and 7 board as 1mono in/2monofx.

Is it right?

[lylehaze]

Almost right.

The software is limited by 16 MIDI channels.

Right now there is just two ways to do each channel:

"Line Mixer" takes stereo In, mixes into Left and Right outputs. Uses Volume, Balance, Master Volume, Expression. Each channel board supports TWO stereo pairs.

"Audio Mixer" takes Mono in, mixes into Left, Right FX1 and FX2. Uses Volume, Pan, Master Volume,Expression, FX1 Level, FX2 Level, FX1 Pre/Post, FX2 Pre/Post, FX1Mute, and FX2 Mute. Each channel board supports ONE mono input channel.

"I've understand we are limited by 16 MIDI channel."

The software limit of 16 MIDI channels can be changed. You'll just need to use a different control change arrangement to make it work. Example: Using CC7 for volume (the MIDI standard) only works for the first 16 channels. You can map other CCs if you want, to make this change, you must re-write the "USER_MPROC_NotifyReceivedEvent" part in the file "main.asm". You will also need to expand the size of the "MIDI1 to MIDI16" table and the "CHANNEL_GAIN" table in app_defines.h. ALL of MBMixer is written in ASM, so you might need to study the code first.

"One board have 4in to 4out so is it possible to use it as 1 stereo input and 1 stereo output and 2 mono fx out?"

If you want to mix a stereo pair into effects outputs, you will only get one channel (left or right) into each of the effects outputs. Right will go to FX1, and Left will go to FX2, I think. If that's what you want, then just set that channel as "full audio mixer" when you configure the software.

"And is it possible to use it as 2 mono input and 1 stereo output with 2 mono fx out?"

No, you need 2 channel boards to do that. There are 4 level controls on each channel board. Each mono input needs a mix into Left, Right, FX1 and FX2. That uses all 4 of the PGA controls on a channel board.

There are 4 inputs and 4 outputs on each channel board to make sure you can always use all 4 of the PGA channels. But mixing all 4 inputs to all 4 outputs is not possible with one PGA4311 chip. Try to think of a channel board as four mono level controls. That is the limit of one channel board. For a "line mixer" we need all four inputs, 2 each left and right. and two outputs, left and right. There are only four levels being controlled. Ch 1 Left, Ch 1 Right, Ch2 Left and Ch2 Right. Each input has only one destination. You can't send a left input to a right output, and nothing is going to the FX sends.

For a "full audio" Mixer we use ONE input, and it is mixed into four possible outputs, Left, Right, FX1 and FX2. There are still only four levels being controlled.

I hope this helps you understand how the channel boards work. I have been working on an audio flowchart that will better diagram the whole system.

"My needs are 9 stereo input and 7 mono input with 2 fx send(if this is possible)."

Even numbers work better. Without any changes to the software, you can set up 10 pairs stereo input (5 channel boards) and six mono inputs with FX (6 channel boards). NOTE: ONLY the mono input channels can mix into the FX outputs.

NOTE: Using 11 channel boards in one stack may require two of the signals from the Midibox to be buffered.

I'm sure there are more questions. This is a great place to discuss it, I'm sure there are other people that want to know the same things.

LyleHaze

[matoz]

thanks, I suspected a little bit this answer.

But i' d like to have fx send with stereo input (excuse me for my determination ;) ). I think now it is possible to group 2 mono "audio mixer" board to make a stereo one. one mono to left, and one mono to right. Perhaps it is possible to group the controls (for example using the same cc, same channel to control volume right and volume left...  and do the same thing for aux send...).

So, for my needs (9stereo input and 7 mono with 2 aux send), i must use 25 "audio mixer" board (9*2  + 7 ).  Right?

[lylehaze]

Yes, with 25 channel boards you can make it do everything except cook your breakfast. You will be able to mix each signal into any combination of Left, Right, FX1 and FX2.

You can even swap left and right inputs per channel as needed.

To do this you will need to make a few changes:

Hardware will definetly require buffers on the SCLK and CS lines coming from the Midibox. Every channel board will be built for one input to four outputs, just like a "full audio" mixer.

Software will require changes so that the MIDI channels that are for the stereo pairs will use 2 channel boards for each pair.

There will be a lot of details to work out how that happens. You will modify the Mid2Gain routine (in setlevels.h) to make it behave the way you want.

I suggest starting with a few channels, just to get comfortable with the system. Maybe four mono inputs into L,R,FX1,FX2, using the software as it is written. You could then use that as a test bed for making the hardware and software changes.

Have Fun,

LyleHaze

[strophlex]

Hardware will definetly require buffers on the SCLK and CS lines coming from the Midibox.

What would be the best way to do this? OpAmp voltage follower?

[strophlex]

I think it would be useful with mute and solo for each channel. That is not implemented is it? I guess it is a pretty easy task though.

[lylehaze]

re Buffering:

There are many ways. I'll try to look up a part number later today.

re Mute and Solo:

Not hard to do these in software. I already did separate mutes for each FX out on each channel. Didn't think of mute and solo for the mains though.

There IS a hardware mute signal, they are all connected together, and you can attach a pushbutton or switch to force mute anytime you want. It's on a pin header on the output board, and it's passed up through the stackpins to every channel board.

LyleHaze

[strophlex]

re Mute and Solo:

Not hard to do these in software. I already did separate mutes for each FX out on each channel. Didn't think of mute and solo for the mains though.

There IS a hardware mute signal, they are all connected together, and you can attach a pushbutton or switch to force mute anytime you want. It's on a pin header on the output board, and it's passed up through the stackpins to every channel board.

I think software would be enough for individual channel mute. The mute all functionallity present today(?), is it controlled via software or hardware?

EDIT: I saw you allready answered that question.

[lylehaze]

Mutes:

Everything today is by software. I joined all the hardware mutes and the Zero-Crossing signals just in case someone wants to play with them. They are currently brought out for selection by jumpers on the output board.

Buffer Chip:

I looked at a few options. I'm not sure which would be easiest to get/already in stock/cheapest. I think I'll leave this alone for now and let someone else figure it out. I'm in the middle of a job search and it is taking a lot of my time. If I don't get back to work soon there will be no new projects for me at all. ;-)

I am favoring a single chip solution, probably piggybacked off of J10, with O.C. outputs. Pullup resistors can then be added to the "top of stack" on those two signals. This termination should provide clean signals all the way up.

I wonder if termination at the top of stack would improve the signals even without a buffer? Seems likely. We haven't even figured out how many channel boards we can drive from a "naked" Midibox J10 yet. I'm running four channel boards with no problems at all.

I am not an expert in this. I am open for suggestions or discussion. I know I'm not the first to gang too many boards onto a Midibox output.

As the core instruction clock is 10Mhz, that means the clock should be able to support 5Mhz as a top speed. That should provide a bit of safety margin.

LyleHaze

[lylehaze]

OK..

Maybe I'm O.C.D. I keep working on this.

There is a good chance that "fan out" may not be a problem at all. According to my most recent research, the impedance of these CMOS inputs is so high that they present almost no load at all.

It may be that all we need to do as the stack gets bigger is to terminate from the TOP of the stack. The boards start at the bottom: Reg Board, Output Board, first channel board etc. Keep stacking as high as you want. Then, at the TOP of the stack, add a 100k resistor from "Chip Select" to "Digital Ground", and another 100k resistor from "Shift Clock" to "Digital Ground".

http://www.midibox.org/dokuwiki/pga:stackboards

These should draw just enough current to keep the noise down, and to clean up the signals that the PGA chips see.

This is definetly the first thing to try if people start building bigger stacks.

I look forward to hearing from people who are building bigger stacks of channel boards.

LyleHaze

[strophlex]

OK..

Maybe I'm O.C.D. I keep working on this.

There is a good chance that "fan out" may not be a problem at all. According to my most recent research, the impedance of these CMOS inputs is so high that they present almost no load at all.

It may be that all we need to do as the stack gets bigger is to terminate from the TOP of the stack. The boards start at the bottom: Reg Board, Output Board, first channel board etc. Keep stacking as high as you want. Then, at the TOP of the stack, add a 100k resistor from "Chip Select" to "Digital Ground", and another 100k resistor from "Shift Clock" to "Digital Ground".

These should draw just enough current to keep the noise down, and to clean up the signals that the PGA chips see.

This is definetly the first thing to try if people start building bigger stacks.

I look forward to hearing from people who are building bigger stacks of channel boards.

LyleHaze

:)

[stryd_one]

We like your OCD. Rock on.

[matoz]

what is OCD ?