thru zero VCO questions

[Martin Czech]

:::> Well, as I mentioned before, sideband separation IS a very difficult task.
:::> -40dB is allready very hard with analog means, but still very audible.
:::
:::Martin,
:::
:::do we need to be so obsessed by the SNR ratings of the VCO output ? As far as
:::I understand, the dynamic range of the synth ouput depends mostly on the per-
:::formance of the VCA. If you consider the masking phenomena, absolute purity
:::of the VCO is not needed. Moreover, a bit of inharmonic remainigs may add some
:::special character to the VCO's timbre. I find both Rene's examples very interesting
:::timbrally.

Well, not obsessed, but concerned...

I think I could not make my point very clear in those few lines.
Sorry for that.

It is not SNR that it is all about, but more interference. And
psychoacoustics. The unwanted sideband is not white noise, it is
a mirror image of your original waveform, tri or sine. Thus it is a
very sharp peak in spectrum. It is very easy for the ear to hear this.
If your wanted frequency goes up, the mirror image (first) goes down,
this will add to the strangeness, but is very undesireble if you simply
want to have good fm. The ear will follow the strange sub signal,
because it moves. The ear is made for this.

And if you chose a fm ratio that enshures harmonic output, it will be very
obvious that the unwanted mirror image will most probably be inharmonic
to it, and this causes other effects, like difference tones in the ear,
which are very unpleasant for that purpose.

It will not sound like fm and white noise, but like fm and someone
trying to annoy you with a strange feedthrough of another oscillator,
or better: set of osc. 

Of course, it may be interesting to hear this interference, but for 
an instrument for general usage it is more than annoying to have allways
something playing mirror melodies with -40dB in the background.

So , for a special effect device with (allmost) white noise live
input the sideband is no problem. I aggree.

But it is not very nice if you want to have clean harmonic or inharmonic
sounds that can be played like the DX series synths.

Nothing is good or bad a priori. The value of a method will only be 
visible with the application in mind.

m.c.