[sdiy] Analog bandwidth

[cheater00 .]

The theory is that if you multiply noise which is just above 20 kHz
(that's your noise), by something that has spectrum between 0 and 20
kHz (that's the envelope), then you get sum and difference. The
difference is at frequency, say, 20 kHz - (something between 0 and 20
kHz), and therefore ends up in the audio band again.

Cheers,
D.

On Sat, Feb 22, 2014 at 5:46 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
>
> On 22 Feb 2014, at 13:45, cheater00 . <cheater00 at gmail.com> wrote:
>
>> On Sat, Feb 22, 2014 at 1:47 PM, Michael Zacherl
>> <sdiy-mz01 at blauwurf.info> wrote:
>>>
>>> On 22 Feb, 2014, at 1:33 PM, cheater00 . <cheater00 at gmail.com> wrote:
>>>
>>>> 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).
>>>
>>> I wonder if this also applies when using programming environments, like
>>> SuperCollider, Max/PSP, Puredata, Csound etc. In theory it should, given
>>> that the basic elements used are pure and 'un-shaped'.
>>>
>>> Michael.
>>
>> Yes, but when doing multiplication or non-linearities or IMD in
>> digital the typical rules for oversampling apply. So you'd have to
>> take, say, a signal that goes up to say 100 kHz, and then oversample
>> it quite a bit.. that's computationally expensive. Why 100 kHz? For
>> example in multiplication you obviously get sum and difference
>> components. So depending on the frequency content of the envelope of
>> your VCA, you'll at most push the noise (which is at 20 kHz - 100 kHz)
>> down by that much. If you want a nice thump you'll make the envelope
>> push down the noise by those 20 kHz or more. As the envelope goes
>> faster, I imagine you would get typical "overdrive" type effects
>> happening on the noise.
>>
>> Andy said he was going to check whether adding some ultrasonic noise
>> makes sense for fast attack settings in his Glue VST but I don't
>> recollect if we spoke about that afterwards.
>
> Sorry, I'm missing something. Why is ultrasonic noise supposed to help with a fast attack?
>
> Thanks,
> Tom
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