[sdiy] using a dac as a digitally controlled amplifier

[Roman Sowa]

If the DAC is 8 bits or less, and passing sine or very low pass filtered 
waveform, the zipper noise will be clearly audible, but with increasing 
resolution and update rate of about 1ksps it should disappear into 
audiophiles-only-can-hear-it region.

Here's and idea, possibly too complex to consider it instead of regular 
VCA, but if you need precise amplitude control, it may be handy. Add a 
comparator working as zero-crossing detector, that when triggered, 
drives the LDAC input of the DAC, literally updating the DAC only at 
szero crossing of the signal, which is in no way to be audible. And even 
with fast envelopes, where each cycle changes in relatively big steps, 
this will be harmonically blended with the synth voice.
Obviously the DAC must have separate input for loading DAC register and 
I can't tell from memory if this is very popular thing in cheap DACs

Roman

W dniu 2024-08-05 o 00:23, Mattias Rickardsson pisze:
> 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).
> 
> /mr
> 
> Den sön 4 aug. 2024 20:48Gordonjcp <gordonjcp at gjcp.net 
> <mailto: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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