[sdiy] Lowest distortion neede for VCA

[rburnett at richieburnett.co.uk]

Log law is common for VCAs in dynamics processors like compressors, 
expanders, de-essers, etc.

Whether the control law is log or linear is just a matter of applying 
the appropriate conversion to the CV before it reaches the VCA.  So the 
type of control law shouldn't influence the ammount of distortion that a 
given VCA imparts on the audio passing through it.

As for how much distortion is acceptable, it depends on the signal, the 
application, and how good your ears are!  If you're feeding something 
like a raw sawtooth or squarewave through the VCA you can probably 
tolerate a huge amount of distortion on paper before you can hear any 
difference to the harmonic structure of the sound.  However, if the 
signal is more complex like a chord or a complete piece of music then 
you won't be able to tolerate anywhere near as much distortion before it 
starts to sound bad.  A very pure sinewave input will also tend to make 
even a small amount of distortion easily audible.

-Richie,



On 2013-09-15 14:48, Harald wrote:
> I am working on a lin VCA. Nothing special, straight forward with 
> LM13700.
> But... there is a tradeoff between THD and S/N ratio. For what 
> distortion
> should i go? I can reach 0.1%. with selectd 13700. Or even better with 
> lower
> differntila input.
> Should there be different distortin between Log and lin VCA? Because 
> lin are
> mostly used for VC processing and log for audio.
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