[sdiy] using a dac as a digitally controlled amplifier

[René Schmitz]

On 05.08.2024 00:23, Mattias Rickardsson wrote:
> Interesting thread.
>
> Do these vintage examples use static amplification factors in their 
> MDACs, or do they allow the digital value be modulated by envelopes 
> and LFOs?
>
> If they do modulate stuff, how is the result in terms of zipper noise 
> etc? Unlike when using a VCA controlled by a CV generated from the 
> very same DAC, there is no way of smoothing out the digital 
> irregularities in the MDAC case. Only perhaps keeping the sample rate 
> above audio (which they probably didn't do by then) or to use clever 
> noise shaping techniques (which also seems unlikely).
>
I did intend to use this in an instrument I built some time ago.

Yes, it does create noise from aliasing if you do not update the DAC 
fast enough. (You'd need a sampling rate well past audio and ideally low 
passes in the signal chain.)

In the end I switched over to a VCA and smoothing the CV instead.


Best,

  René


> /mr
>
> Den sön 4 aug. 2024 20:48Gordonjcp <gordonjcp at gjcp.net> skrev:
>
>     On Sun, Aug 04, 2024 at 06:26:06PM +0100, Tom Wiltshire wrote:
>     > The Synclavier used DACs for VCAs like this too, fed with audio
>     from other DACs. In that case it was a way of avoiding doing
>     multiplies in hardware and not losing any resolution.
>     >
>
>     The Ensoniq DOC chip uses the same trick for the same reason.
>
>     -- 
>     Gordonjcp
>
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