MIDIBox Mixer - A PGAx311 Audio Mixer

[lylehaze]

It's working. :-)

I only have the first 4311 wired in yet, but today I was able to power it up and control the levels from a remote

MIDI console.

Sound quality is excellent.

Since I'm hand-wiring everything but the core, it's going

a bit slow, but it is going well.

I should have it far enough along to photograph and document it within a few weeks.

MIOS Rocks.

LyleHaze

[widdly]

Congrats Lyle.  Looking forward to seeing the photos and docs on this one. 

On a related note I found this page about a PIC controlled mixed using LM1973 chipos which are three channel digital pots.  They are using op-amps for output buffering.  The interesting part is the way the LM1973 could be daisy chained so one basic pcb could be designed and then any number of these pcb's could be connected to create the desired number of channels

http://www.andrewkilpatrick.org/mind/ir_mixer/

[lylehaze]

Looks good.

The PGA chips have the same connections. There's an enable

and clock that go to all, and data that goes from each chip

out to the next in.

I've been too tired to build boards this weekend, but I did some more work on the MIOS code. I've got two pairs built and working, and they are controlled by CC#7(Volume) and CC#8(balance) right now. The front panel encoder can also adjust them, and it sends out the same CCs to keep the controls updated. The channels are named, so when I tweak channel one it displays as "CD Player", channel two is my computer, etc.. Now I'm working on using the bottom line of the display as a stereo VU meter. I'm halfway through the display code for that.

I thought about putting the project up on the WIKI, but I'm afraid I'll screw up the webpage or something.

The board has been powered up and working 24/7 for over a week now. So far it's working solid and sounding sweet.

Time to go to work..

Lyle

[cimo]

hallo

i am very interested on this project, i use an external audio mixer while i spin with a pal (turntables vs. laptop figthing, that s the way we call it) and i d love to change the mixer for a digital mixer to control directly from my MB.Now does anybody of you thought about eq kill switch or eq pots? would that be possible to implement some filters and digital switches to be controlled via MIDI?

simone

[lylehaze]

Cimo,

I'm sure it could be done. My design is just a "line mixer" with nothing but volume and balance or pan (it follows both balance and pan controls). I'm thinking that a basic EQ is just a couple low and/or high-pass filters, each with it's own level control. That shouldn't be too tough. I tried to write the controls in a way that's easy to change around.

The PGA4311 does four channels, that could easily be Bass, Mid, Treble, and Main Level for a single channel. It'll take a lot more chips to get the job done though.

I need to get this thing posted to the Wiki so others can play with it a bit. I finished the meter code, all I have left is a way to adjust the balance from the front panel. I'm beginning to wonder if I'm putting too much stuff on a single encoder with pushbutton. :-)

I also need to finish building the boards. The first two pairs are working great, but I have parts, space, and the need for six more pairs. I guess I can post the project anyway, I'm sure it's working.

I'll try to get some more documents written at work tomorrow. The text is easy, but the schematics take more time to do. I could lay out Eagle boards too, but the more I try to get done, the longer it will take. Maybe I should post what I have already and go from there.

Time to sleep,

LyleHaze

[cimo]

hi lylehaze

when you will release the infos i could take over the whole (or part of it) eq stuff, i became quite familiar with eagle and i will have free time to toy around with it during the summer.

simone

[Lall]

Hi Lyle,

All that is really excellent news. Excellent.

I've just received the PGAs last week  ;D. I think I'll try to finalize my SEQ first, too much distraction now will make it shift further away again. But then sure I'll give that a try. I think of using such a stage as a mixer output for my quad SID to come and spare on inputs of my mixer console which is already too much crowded.

Best regards,

Lall

[lylehaze]

I've been busy with the software in the mixer.

Channels are now named. Local and remote (MIDI)

controls are working great. There's a cool

horizonital bargraph to show level and balance

settings for each channel, but I doubt it will

work with all displays. I need to put Pilos

Db display back in as an option.

Last night I changed the response from linear to

LOG. MUCH nicer feel to the controls now.

Oh, and I wrote a little app for my computer that

let's me create and send SysEx files to display

text on the Core display, just for fun.

I have built all the remaining audio buffers, and

I've started on the rest of the PGA4311 boards.

Now if I can just finish the boards, I'll be ready

to take pictures and post everything.

If anyone is waiting for the code release, just ask

for it. It's definetly far enough along to share if

anyone else wants to build an audio mixer.

all the while listening to "Back Against the Wall"

sounds great. ;-) MIOS Rocks!

LyleHaze

[stryd_one]

Great stuff :)

If anyone is waiting for the code release, just ask for it.

OK. Gimme! ;D I've been watching this and the PGA is on my bench waiting :)

[lylehaze]

@stryd_one

Check your hotmail.

And please, remember that I'm new here.

If you have any suggestions, I would LOVE to hear them.

Thanks,

LyleHaze

[lylehaze]

In case anyone is interested,

http://www.midibox.org/dokuwiki/doku.php?do=show&id=midiboxmixer

The project is now online (with a little help from my friends);-)

The documents are not static, I'll be editing things around a bit to make it as easy as possible.

I welcome any suggestions on how to present the information better.

Also, there are some pictures in the end of the hardware section.

LyleHaze

[TK.]

Thank you, Lyle! Thats a great and especially very good documented project! :)

I will be propably one of the first users, as I already own the chips, mounted on a PCB and ready for use (@doc: thanks again! :)) - I'm planning to use MBMixer to mix the audio outputs of my MIDIbox SID, MIDIbox FM and the 4 CEM3378 filters with total recall capabilities.

The project is now also listed in the navigation bar of ucapps.de

Best Regards, Thorsten.

[Roelli]

Hi all.

The midiboxmixer looks damn interesting!  :)

Iam thinking about how to use it with my analog console and remove the faders and replace them with motorfaders and replace the 10k pot of the fader

with 1/2 PGA2311.

Can I use 12 of the stereo PGA2311 to get 24 channels and control each channel seprately over midi volume control?

This could make a 24 channel flying fader automation together with 3x MotorFader Modules!?

I could use the volume automation of the cubase sequencer to record the fader positions...

Is it then possible to use the motofaders with touch sensors to record the fader moves into cubase while the midiboxmixer

will control the analog volume of every of the 24 channels of the console? (ok, i have to add a PSU and input buffers to

all channels of course)

Any ideas?

Thanks,

Frank.

[Roelli]

ah... i don't think its a good idea to use one of these attenuators as a replacement for faders because of the zero detection...

I have a normal vca automation somewhere... i think i could use it. (controlled by the MotorFader modules).

Or use the AOUT Module to control a vca.

Would be much better, or am I wrong?

Thanks,

Roelli.

[Ashiman]

The purpose is:

If I use the digital potentiometer in audio volume control, will I experience zipper noise?

There is a noticeable zipper noise. However, we have developed an external zero-crossing detector that effectively reduces the zipper noise. Please refer to AD5290 datasheet Audio Volume Control section

for synth usage I would definately forget about it.

Here is how you make CV controlled VCA (definately employed in mixers , look at patent filled by Sony itself, think of the Oxford mixer fame  )

http://tinyurl.com/36vrq7

http://www.thatcorp.com/datashts/an102.pdf

[Ashiman]

judging by the popularity of this topic , "analog saturation" isnt the magic word around here LOL!!! You ppl should definately look at what comes out of the back of an analog mixer, its full of added harmonics. With these PGA specs in mind , you might as well sum in digital realm , 1+1 = 2 !!!!! sorry im drunk

[Ashiman]

i wanted to use these IC's for preamplification before the big wattage, but digital stuff effectively scared me away. Now Im into discrete, but my crossovers will be digital  ;)

here is how the pga looks in discrete:

http://www.acoustic-dimension.com/attenuators/attenuators-main.htm

now imagine, you only step back & forth when ... (or not)

[lylehaze]

I'm glad the mixer looks interesting.

It's been in use daily since it was first released here.

You asked about using Motorfaders AND PGA chips.

Yes, I suppose you can, but usually (if I understand you right) you would use one or the other.. Motorfaders alone can do volume control without PGA chips.

The reason I went with the PGA chips is that there are no moving parts, and no pots or switches to get dirty over time. So the performance should be just as quiet in ten years as it is today.

As far as sequencing a mix, yes, absolutely! The current

software provides for up to sixteen stereo pairs, handling volume and pan for each pair. Of course you can change this, but I wanted it to match the sixteen channels of MIDI, so I went with the more obvious route. I can currently mix from a board of encoders and from my sequencer and use presets from a script file, all active at all times. It's really handy to type "mute" into a command shell and have all the audio drop out instantly.

Zipper noise? Yes, I've heard it under some extreme conditions, but it's not a big problem unless your final amp gain is set way too high. (which may be normal for some people ;-) )

The PGA chips have a zero-crossing option built in.

Anyway, yes, the board still works, and sounds pretty darn good, too. If I can be any help, just ask.

LyleHaze

[Ashiman]

yeah, pretty much. The choice is yours. You want to employ the zero crossing trickery , or you want to employ the voltage out DAC for CV. First is transparent, second is conventional and can we say, universal. Take your pick!

[gavgomad]

I keep coming back to this project as being a great centerpiece for my rig... Great work guys!  ;)

Just thinking aloud.... Not being a hard core programmer type, how hard would it be to address the individual PGA channels separately? My needs for a submixer aren't vast for my live rig, so probably 8x stereo channels would do the job. What would be nice, however, is to wire another 16x mono channels as mono effects sends (send 1 and 2 per channel - or perhaps one single stereo send?).... How difficult a job would this be?

This might also be helpful for those who may want to save some PGAs as they have mono gear, as some PGA channels can be configured as mono inputs....

Also, I recall TK talking about this awhile back.... does the software currently have facility for storing scenes?

Gav.

[Ashiman]

ok i gave up before someone comes and ask for balance out SID's

[lylehaze]

Yes. mono controls would be a simple change.

Right now the table of stereo settings (volume and

balance) are read and converted to a table of 32

monophonic levels. These are then changed from

linear to log and then they get sent out.

You could simply maintain the 32 levels directly

and everything would work, with or without the

log conversion.

For scenes, Pilo has written a single frame

snapshot routine that could easily be extended.

I'm not using it but the code is included.

For panning a mono signal into a stereo pair, it

would be easiest to feed the signal into the stereo

design and just use the balance/pan control for

position.

LyleHaze

[dj3nk]

Dont know if it is useful or not and I dont have tested it yet, but if anybody wants the .brd please pm me.

http://www.midibox.org/forum/index.php/topic,10422.msg78766.html#msg78766 (THREAD CLOSED NOW!) REPLY HERE!

greetz

[lylehaze]

Wow, Looks great!

I have been trying to get around to doing a board layout

in Eagle, but there's never enough time.

If I can make a few suggestions:

There should be pull-down resistors between each SDO

and SDI pin.. and there should be about four capacitors

for each PGA chip. I can send the datasheet with that

stuff shown if you want it.

If you are having boards made, PLEASE let me know.

I'd love to have a couple made for me too, if I can afford them.

Yes, you can add this board to the WIKI if you want.

Maybe we should wait until we have one built and working.

Thank You,

LyleHaze

[dj3nk]

Yes, I'll make these changes in the layout these days. I hope that I will find some time soon to etch a test pcb. I already have some 4311 lying around :D .

I'll pm you my email address so you can send my the datasheet. And of course you will be the first who gets the pcb ;) .

greetz