[sdiy] Analog bandwidth

cheater00 . cheater00 at gmail.com
Sat Feb 22 13:33:50 CET 2014


Hi Rutger,
when you're creating a VST emulation of a synth you usually get a unit
or a couple and hook it up to an oscilloscope and spec an to see
what's really there. So it doesn't make sense to ponder whether
generally it's worth modelling above 20 kHz, 15 kHz or 5 kHz - it'll
come out on its own, on a case by case basis.

I believe adding shaped, ultrasonic noise before a VCA is a way to
shape transients during fast A/D/R stages. It should also work in a
compressor (you must not add the noise to the sidechain, though).
Finally anything with a non-linearity, which is pretty much anything
we use. I don't remember if I have tried any of those, though. An
alternative to using shaped noise is to use a signal harmonically
derived from the oscillator, and it could work better if it's a
multi-osc signal (as then you are doing IMD between uncorrelated
sources). So for example an oscillator that has harmonics well beyond
20 kHz. Say, up to 200 kHz.

Cheers,
D.

On Sat, Feb 22, 2014 at 12:35 PM, Rutger Vlek <rutgervlek at gmail.com> wrote:
> I totally agree with you! And just to be clear: I'm not saying that anything above 20k doesn't matter. I'm just saying that many old synths were designed in a way that doesn't do justice to supersonic signals either (slow opamps, and choice of LPF capacitors in opamp stages). So from a point of modeling, I'm just wondering if it makes sense to go there. A far more interesting direction would be to design a new synth that explicitly handles supersonic material in such a way that it influences the sonic range in a nice way by means of the modulation types you describe.
>
> Rutger
>
>
> On 21 feb 2014, at 20:09, cheater00 . wrote:
>
>> Hello,
>> signals which are inaudible are very important when performing
>> outright ring modulation, pitch shifting (including chorus), and when
>> doing things that push supersonic information down into the audio
>> band: amplitude modulation (every single processing stage in a synth),
>> multiplication, non-linearities. Saying that it doesn't matter because
>> you can't hear above 20 kHz is a cop out.
>>
>> Cheers,
>> D.
>>
>> On Fri, Feb 21, 2014 at 6:56 AM, David G Dixon <dixon at mail.ubc.ca> wrote:
>>>> I think that many old synths were also designed with the
>>>> knowledge in mind that we can only perceive sounds up to
>>>> 20kHz.
>>>
>>> I can only perceive sounds up to 13kHz.  That's why my whole world sounds
>>> full of warm analog goodness!
>>>
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