MIDIbox Analog Audio Mixer

[Hawkeye]

Can we build a MIDIBox audio mixer? I mean MIDI-controlled and digital for motorfaders and total recall, bundled with a purely analogue mixing engine?

inputs:

8x stereo in (also connect fx send returns here)

usb (core32)

midi in (core32)

power (motorfaders)

outputs:

8x direct stereo out (for directly recording the inputs)

2x stereo fx send out

1x stereo mix out

midi out (core32)

control surface:

one motor fader per channel

two motorized potentiometer fx send channels per channel

two motorized potentiometers for analogue stereo mixing (used internally only) per channel

no hi/med/low equalizer/sound adjustment stage for pure sound per channel

sound input level meters per channel ("stereo" level meter LEDs)

sound output level meters for mix out ("stereo" level meter LEDs)

mute button + LED per channel (-> alters motorized mixing potentiometers of this channel)

solo button + LED per channel (-> alters motorized mixing potentiometers of the other channels)

small character lcd or vfd for mixing info

I´d be willing to code the app, but have no plan in hardware design ;-).

Any thoughts?

Bye,

Peter

Edited December 3, 2010 by Hawkeye

[nILS]

Doable. Pricey.

[ilmenator]

The audio circuitry could be based on Lyle's project, I'm sure he has some valuable comments to give! If you make all the fancy, expensive stuff optional this could become an interesting project.

[Hawkeye]

I did not do much market research, but i´d be willing to sacrifice a small toe for a thing like this, if the audio quality is decent. Best of all: no frills/gimmicks... and shelling out 1.5k bucks for a digital mixer made in china isnt cheap either...

Edit: Lyle´s project page contains a wealth of information... thanks, ilmenator!

Edited December 3, 2010 by Hawkeye

[JRock]

I don't know if this helps at all but I found this on the MFOS website... Maybe helps with the hardware aspect? Here's the link:

MOTM Panning Mixer

Looks pretty simple to build a basic hardware mixer, maybe you can add or extract some of what you need from this schematic...

I found this after searching for a while cause I needed more input channels after I built the MB6582 and got a S900. I think I decided that for the price of a good mixer and the time it would take I'd rather spend my DIY time doing other things. Good to keep in mind for a little mixer (for a modular? or MBFM?) someday though.

Hope this helps :thumbsup:

[lylehaze]

My project has been quiet for a long time, but it IS in active service every day, and

the "new" board design has not been abandoned.

I would be happy to offer any info that you want. Perhaps this would be a good time

for me to flowchart the math array that I wrote in PIC assembler, for the purpose of

public discussion and perhaps even a C translation.

I have also forked the project into a smaller, simpler device that "dead mixes" four

stereo pairs with no individual levels, but then gives a PGA level control on the

summed stereo output. This smaller variant has two target purposes:

Folks with multiple computers and a single set of speakers, and cheap people

that want to use a $30 set of 2.1 computer speakers instead of spending a few hundred

on a fancy "Home Theater" set.. Oh, did I mention it is controlled by a TV remote?

I DID keep the UART open for MIDI,USB, or Bluetooth stuff too.

Anyway, I'll be around the house a lot for the next three days (That's unusual for me)

so if there's any questions I can answer, I'll try to check in every few hours.

LyleHaze

[Hawkeye]

@Lylehaze: thanks for the quick feedback!

I am still building another project and would rather not mix things up (literally ;-)), so there is no need for haste ;-)

How would you classify the audio quality of the 4311? Good enough, even when they are cascaded? Do you have any thoughts regarding the internal audio amp? I ask this, because commercial mixer vendors highly stress their amplification stages (and come out with new names for them every other year ;-).... Sorry, questions over questions ;-)

I´ve had a quick peek into the tech specs... the serial mixer communication reminds me of my latest adventures with VFDs :-)... but yes, this will work ;-)

sorry can´t say more at the moment, gotta dig deeper into the matter first ;-). Also, I fear, that I do not have enough hardware experience to pull this off :-(.

@jrock: thanks a lot... did not look into it in detail yet....... are the tl084 audio amplifiers good enough? Lylehaze´s approach using dedicated mixer chips controlled by the core is very neat and seems superior in terms of price, speed and resolution to motorized potentiometers for mixing... on the other hand... the circuitry is completely passive if we ignore the tl084s... if we use some very high quality amps... i could imagine the sound quality being superior to a cascade of 4311s... i just don´t know and have no means and experience to measure or judge it :-(

---

Btw: i found this chip to realize the led audio level bars: http://www.national..../LM/LM3915.html

Have a nice weekend!

Peter

Edited December 4, 2010 by Hawkeye

[lylehaze]

@Lylehaze: thanks for the quick feedback!

I am still building another project and would rather not mix things up (literally ;-)), so there is no need for haste ;-)

How would you classify the audio quality of the 4311? Good enough, even when they are cascaded? Do you have any thoughts regarding the internal audio amp? I ask this, because commercial mixer vendors highly stress their amplification stages (and come out with new names for them every other year ;-).... Sorry, questions over questions ;-)

I´ve had a quick peek into the tech specs... the serial mixer communication reminds me of my latest adventures with VFDs :-)... but yes, this will work ;-)

sorry can´t say more at the moment, gotta dig deeper into the matter first ;-). Also, I fear, that I do not have enough hardware experience to pull this off :-(.

@jrock: thanks a lot... did not look into it in detail yet....... are the tl084 audio amplifiers good enough? Lylehaze´s approach using dedicated mixer chips controlled by the core is very neat and seems superior in terms of price, speed and resolution to motorized potentiometers for mixing... on the other hand... the circuitry is completely passive if we ignore the tl084s... if we use some very high quality amps... i could imagine the sound quality being superior to a cascade of 4311s... i just don´t know and have no means and experience to measure or judge it :-(

---

Btw: i found this chip to realize the led audio level bars: http://www.national..../LM/LM3915.html

Have a nice weekend!

Peter

Wow, I just booted into Chrome OS for the first time.. let's see how well I can post. :)

Timing: Anyone who has followed my mixer project knows that things move very slowly.. So don't worry about a thing. If you need me in a hurry, just e-mail to my nick at gmail.. that account is checked at least once a day no matter what.

The sound quality of the 4311.. there are a few answers I can give you. Please forgive me if I say too much, better that than not enough:

As far as I know, I am the only person on the list who has actually heard my mixer. I am very "picky" about sound quality, but I'm not one of those audiophiles that spends $300 on gold speaker cables.. So it may be hard for you to decide what my opinion is worth.

While static, with no levels changing, the sound quality is well beyond my ability to find fault. It really sounds transparent. When the level is jumped directly from one level to another (not quite possible with faders) the change is quite abrupt (as expected) and also excellent. While slowly fading.. the step size is as low as 0.5 dB, and there is no noticeable "zipper noise" across MOST of the range, but since the level goes through a log conversion, the steps get bigger at one end of the scale. I am considering re-writing the math to change this. The only time I hear "noise" in my audio is while dumping SysEx to re-flash the PIC.. I can hear each burst in the background. More details: the PCB layout and grounding techniques will affect sound quality more than anything else.. Version 1 was hand-wired, and sounded pretty damn good. Ver2 are the pics shown in the WIKI with the boards stacked. The "latest" Ver 3 boards have been layed out, but not fabbed yet. So if someone tells you they have heard my mixer, they are probably not quite telling the truth.

"Even when cascaded"?? Two possible meanings:

The digital controls are cascaded from chip to chip. This will have no effect on sound quality.

The Audio path (By the way, is ALL ANALOG) is NOT cascaded in my mixer. This is one of the "unique" qualities of doing it the way I did. Allow me to explain. Assuming a "Full Audio" mixer configuration, each single input is handled by a single PGA4311 chip. the controls available APPEAR to be cascaded.. You'll have an input gain(expression), a main level control, a PAN control, and two available effects loops, each with an effects level AND a pre/post fader switch. Finally, a "master" level will affect the left and right channels across the board...

Now, in a "classic" analog mixer, there would be a fader or pot for each of those controls, all cascaded however the designer intended.. and in MY mixer, the controls will APPEAR to work the same way. but in reality, the each of the four channels of the PGA chip will feed the signal DIRECTLY into Left, Right, FX1, and FX2. So all the "magic" happens in the software, combining all the various control values into a final result for each PGA channel. Result, the audio will pass through ONE PGA fader for each output stage(s). I hope that made sense, since it's one of the "cool" advantages of my design.

Enough about sound quality. I am very satisfied with it, and I look forward to getting other peoples ears involved.

Amp quality? The op-amps I use are simple and clean. No frills, no advertising, just a clean signal. :)

Scared of SMT chips? The PGAs are easy enough to solder, but 2 channel versions are also available in DIP form if you want to experiment. you'll just need twice as many to get the job done, no changes in software.

Want to play? Somewhere in there is a JAVA program that will let you design an on-screen mixing console with any knobs/buttons/graphics you wish and completely configurable MIDI options too. Whichever way you go, it might be handy for testing. :)

I'll write more later, but I'm tired right now.

LyleHaze

P.S. Chrome OS is cool.. not quite ready for prime-time, but I didn't even install it on the HD, I just made a bootable USB flash drive.

Edited December 4, 2010 by lylehaze

[Hawkeye]

Hey,

that sounds very nice, all in all... thank you for your long description of the audio quality - that is good enough for me... :-)

btw. with cascading (sorry for the unclear description, it is not my native tongue ;-)) I meant the audio signal going through multiple chained 4311s, which I think would worsen the sound quality (as it goes through multiple amp stages) - but this is not the case in your design and this is very good :)

When my other project is finished and my government grants me another time segment ;-), there are two ways to continue...

a) use your mixer pcbs and extend the design with motorfaders for volume control and encoders for panning and fx sends ... if possible, I don´t want to dive into core8 programming.. maybe there is a way to connect everything to a core32...

b) use an own approach with the 4311s... I just had the following idea allowing for an arbitrary number of mixing channels only involving one 4311 per mono input channel, I would love to hear your comments on that :)

audio in socket 		

   |        	

direct out  socket

   |

   |_ input led level meters  (higher than 10 led per channel resolution can be obtained by cascading the lm3915s)

   |

   |_ 4311 (same audio signal connected to audio in ports 1...4)

 		|_ mix audio out 1: fx 1 send

 		|_ mix audio out 2: fx 2 send

 		|_ mix audio out 3: fx 3 send

 		|_ mix audio out 4: master bus send

and then on each mono master bus, use a plain and simple passive audio summer (resistors) configured for the correct number of channels (e.g. 8 mono channels) Edit: as far as I understood now, you do exactly the same... the passive summers are not necessary, if the master bus send signal from above is attenuated enough to allow for simple connection linking. right? if so, that is great, but one might nevertheless use a passive summer to increase resolution, as the attenuation would have to be done using only 8-bit volume controls on every channel... to keep the cost of the control surface down, per stereo channel, one could use (from top to bottom):

   an endless encoder for input gain  

   an endless encoder for stereo panning

   three endless encoders for fx1-3 sends 

   (all endless encoders optional with led rings from a led matrix)

   one motorfader for volume control, 

   buttons for solo and mute.

What do you think? If I by mistake reused any of your ideas, please accept my apologies...

Thanks and bye,

Peter

Edited December 4, 2010 by Hawkeye

[lylehaze]

Hey,

that sounds very nice, all in all... thank you for your long description of the audio quality - that is good enough for me... :-)

btw. with cascading (sorry for the unclear description, it is not my native tongue ;-)) I meant the audio signal going through multiple chained 4311s, which I think would worsen the sound quality (as it goes through multiple amp stages) - but this is not the case in your design and this is very good :)

When my other project is finished and my government grants me another time segment ;-), there are two ways to continue...

a) use your mixer pcbs and extend the design with motorfaders for volume control and encoders for panning and fx sends ... if possible, I don´t want to dive into core8 programming.. maybe there is a way to connect everything to a core32...

b) use an own approach with the 4311s... I just had the following idea allowing for an arbitrary number of mixing channels only involving one 4311 per mono input channel, I would love to hear your comments on that :)

audio in socket 		

   |        	

direct out  socket

   |

   |_ input led level meters  (higher than 10 led per channel resolution can be obtained by cascading the lm3915s)

   |

   |_ 4311 (same audio signal connected to audio in ports 1...4)

 		|_ mix audio out 1: fx 1 send

 		|_ mix audio out 2: fx 2 send

 		|_ mix audio out 3: fx 3 send

 		|_ mix audio out 4: master bus send

and then on each mono master bus, use a plain and simple passive audio summer (resistors) configured for the correct number of channels (e.g. 8 mono channels) Edit: as far as I understood now, you do exactly the same... the passive summers are not necessary, if the master bus send signal from above is attenuated enough to allow for simple connection linking. right? if so, that is great, but one might nevertheless use a passive summer to increase resolution, as the attenuation would have to be done using only 8-bit volume controls on every channel... to keep the cost of the control surface down, per stereo channel, one could use (from top to bottom):

   an endless encoder for input gain  

   an endless encoder for stereo panning

   three endless encoders for fx1-3 sends 

   (all endless encoders optional with led rings from a led matrix)

   one motorfader for volume control, 

   buttons for solo and mute.

What do you think? If I by mistake reused any of your ideas, please accept my apologies...

Thanks and bye,

Peter

It's all good. I don't want to "take over" your project, but I'll toss out a few ideas for you to consider.

One of the unusual advantages of my mixer design is the separation of the audio

handling from the controls. This offers a few cool tricks: In a live music application, the

mixer can be placed backstage, and the controls located a long distance away. This gives a

much easier setup, as the "snake" connecting them can be as small as a pair of MIDI cables,

or better, a single CAN cable. This is much better than running all the audio up to the booth to be

mixed and run back down to the stage. It also offers the advantage of allowing multiple points

of control, each one being a hardware device (MB64e?), a software board like my Java XML mixer,

or even a sequencer that might be linked to a bigger system. Of course, all the controls respond

to remote commands so you can see what's really happening.

There's a hardware cause too. The PGA update cannot be interrupted, and it already takes just a

bit longer than a MIDI byte time, so I do not recommend using the same Core8 for the PGAs and

a user interface. Things work better if you separate them onto different cores.

Everything mentioned above is already complete. what comes next is one of the things I am working on:

If you want to separate the controls from the mix deck, I suggest a simple integrator circuit on each

channel input, with the resulting analog voltage being read by a PIC and transmitted. this will allow

you to see the levels from any/all of the remote sites. I already wrote the display code into the XML mixer,

and breadboarded a hardware circuit, but have not finished it out yet.

It will create a lot of MIDI traffic. I have been watching MBNet with interest, as CAN is looking better

all the time! (Great for long distance fast comms)

Regarding the 8 bit resolution: MIDI supports 14 bit resolution, though most control surfaces only use

7 bits. There is no reason the whole MBMix program cannot be re-written for 14 bits of control sensitivity

completely in software. The PGA chips support 0.5dB resolution.. and even at 7 bit, the combination

of multiple controls results in a higher res than that.

Let me say again: I don't want to take over your project. This is a DIY community. I released my code so that

anyone can take it anywhere they want. Oh, re-writing MBMix for Core32 should not be a problem at all, except

that I don't have a Core32, and I have very little time too. The actual program logic is very simple, and the

math is too. I WILL support anyone who wants to re-write it for the Core32 in C.

I lost a fingertip a few weeks ago, so I have to keep my typing in short spells. (Ouch!) Maybe better after I get all

the stitches out.

Have Fun,

LyleHaze

[Hawkeye]

Ouch! Hope your hand is getting better...

It really seems that your designed Mixer PCBs are very nice ... It should not be too much hassle to integrate them with the Core32 and then it should be quite easy to create a decoupled user interface... Or just create a Core8/Core32 Control Surface and control everything via MIDI... I also like the idea of separating the mixing desk controls from the big cable mess :-).

Your project has provided a wealth of information, big thanks! Will have to finish that MBSeq first before further planning :-)

Bye!

Peter

Edited December 4, 2010 by Hawkeye

[lylehaze]

The XML mixer was buried deep in the miscellaneous pile.

It's an early rev, and NOT as good as a real control surface, but valuable for testing and prototyping, at least.

Not my proudest work, but usable. Making knob images of Cartman, Stan, and Kenny was fun. :)

LyleHaze