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Digital Audio Control Mixer Project

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GooseElectro

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Digital Audio Control Mixer


I want to make a device/mixer that can digitally control the volume, balance and mute (on/off) of several stereo line level audio inputs and outputs. I need to be able to choose which outputs each input signal will be sent to. I also need a master volume and mute control that will control all the outputs at the same time.


I want to be able to control this using an IR remote control but maybe from other things like a PC or maybe an iPhone.


**broken link removed**


Here are some examples of what I need the device to do:


**broken link removed**


If it were a non-digital mixer (i.e. it had manual controls), they would look like this:


**broken link removed**


I can think of two ways to do this:


1. Use digital pots or volume controls for the volume, (I don’t know if the pots will do or will u need the real thing made for audio?), Use relays or transistors to mute the signal OR just put volume to zero? For balance use extra control or individual volume controls for each stereo channel (L/R)? Use a micro controller/processor of some sort that will interface to the controls (volume IC, etc)?

2. Use some sort of digital audio processor?
 

keny

New Member
so are you trying to get gain out of it or do you just want to control the level of the input signal? You could have a significant improvement in quality if you used a passive circuit, i.e. stepped attenuators instead of preamps to control the "volume" BTW the first " volume would be 'gain' or trim and the second would be fader, and the only appropriate one to use a preamp would be the input.

For quality: My recommendation, use one attenuator per channel and no amplification at all. Most of the times HI-fi amps are left on high and the input signal is the signal that controls volume.

Then you make a simple pwm remote circuit that drives relays for the different channels. Then you just use a selector to control the different attenuator levels.

kiwame resistor page
 

mbarazeen

Member
why do you want to control the level at the input and the out put? your out put slect may put two inputs together in one out put channel, you mean to have a mixer by that? or you only need a matrix switch to slect only one input for a particular output?
 

keny

New Member
yea but im thinking thats the standard of this type of thing.... maybe a good example to mock the setup.
 
For the pots you can get digital pots which are controlled by a micro-controller (e.g the pic16F877) and have a variable resistance

have a look here : **broken link removed**
 

GooseElectro

New Member
so are you trying to get gain out of it or do you just want to control the level of the input signal? You could have a significant improvement in quality if you used a passive circuit, i.e. stepped attenuators instead of preamps to control the "volume" ...
kiwame resistor page

I dont need any gain from the whole circuit but i need the output to be the same line-level as the input ( no loss ). Do u think a passive circuit would be as smooth on the volume change and do u think that would sound better than a volume control chip that is made for the job, e.g. PGA2311 - stereo audio volume control?
 

GooseElectro

New Member
why do you want to control the level at the input and the out put? your out put slect may put two inputs together in one out put channel, you mean to have a mixer by that? or you only need a matrix switch to slect only one input for a particular output?

I need to be able to choose and mix the inputs and control the volume of the mix/ output look at the diagrams.
 

GooseElectro

New Member
For the pots you can get digital pots which are controlled by a micro-controller (e.g the pic16F877) and have a variable resistance

have a look here : **broken link removed**

Yes i have found this before. I am not sure if they would work as well as a digital volume control, e.g. PGA2311 - stereo audio volume control?
 

keny

New Member
Typically stepped attenuators work in steps, but the overall audio quality is a lot better than pot's because you don't get any noise or distortion, just a mirror image of the input but quieter. You can choose a few steps or a lot of steps. I come from audio recording studios, where the mains are listened to when not making dynamic changes to them. If you are DJ-ing thats a different story...

this is the mother of all studio monitoring setups (it has "programmable input gain offsets"):
**broken link removed**
 

mbarazeen

Member
I need to be able to choose and mix the inputs and control the volume of the mix/ output look at the diagrams.

thats fine, but still you have to consider one point, for example if you need the input#1 to be mixed with input#2 and input#3 and the output is to be on ouput#1, Output#2. you can not have different level of input#1 at both out puts.

inclear word when input #1 is connected to two outputs, the level of input#1 to the mixer of both output channels would be the same.
 

GooseElectro

New Member
thats fine, but still you have to consider one point, for example if you need the input#1 to be mixed with input#2 and input#3 and the output is to be on ouput#1, Output#2. you can not have different level of input#1 at both out puts.

inclear word when input #1 is connected to two outputs, the level of input#1 to the mixer of both output channels would be the same.

i think i follow what you are saying. That is a good point i had not thought of. However i dont think this will be a big problem and it would add to the ammount of controls, maybe too complex to use.
 

mbarazeen

Member
i just sketched to show how you can intergrate your controller in the mixer. i hope you can use a PIC controlle i am not familier with it but some one can adwise you. also i dont know a single PIC can handle all the requirement. its just and out line. see the attached pic.
 

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