[sdiy] (Ab)use DAC as mixer?

[Tim Ressel]

Check out the datasheet for the AD7225 quad 8 bit MDAC. It has some cool 
examples.

--timmers


On 6/2/2018 12:40 AM, sleepy_dog at gmx.de wrote:
> Hey list,
>
> this has been floating around in my mind for some years and I just 
> remembered it again, so maybe some of you know something about this:
>
> Would it be feasible to "abuse" a quad DAC with 4 independant Vref 
> inputs as a 4 channel, digitally controlled  mixer?
>
> I.e., you feed in 4 analogue voltages into the 4 Vref inputs, and 
> control the volumes by writing digital output values.
> The DAC I had in mind (TLV5620, price OK) only has 8-bit resolution 
> and can stomach only 1/2 Vcc (1.65V I believe),
> and it's positive-voltage-only, but that would do away with so much 
> effort, in comparison to other solutions I'm aware of...
> So If I have up to 4 audio sources which are already positive-only, 
> *some* of which might come out of a DAC and not yet put through a 
> reconstruction filter,
> I could mix them all that way, and put only one reconstruction filter 
> for the mix?
>
> Yeah, it's for something like waveform mixing. Not planning on a high 
> update rate for the digital volume levels (so far), just manual knob 
> adjustment. Although I could imagine it might be cool to modulate that 
> somewhat, if that doesn't get too noisy.
>
> But the layman I am, I probably don't know about some horrible side 
> effects that may have :-D
>
> What can you say about the feasibility of those two aspects (and then 
> others I may have overlooked):
> 1) using a DAC this way in general
> 2) my desire to skimp on the number of reconstruction filters, 
> filtering the mix (I'm not sure I'd be using > 1 DAC output for audio, 
> but keep it in mind as an option, when DAC resolution is moderate)
>
> - Steve
>
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-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com