[sdiy] Polyphonic tonal disorder!

[Steve Lenham]

From: "karl dalen":


>With the old polys some users complains about that the next note plated
>dont sound like the previous played, it depends on the poly alg used
>off course,whether its voice repeat or step trough all voices at each note
>etc.
>Also people of single oscillator polys almost never complaints about
>polyphonic tonal dissorder compared to 2 or more oscillator per voice 
>polys.
>Perhaps because that its easier to hear the disorder of 2 oscillators
>for then same voice compared to the one oscillator based chord? No?

I've just serviced an Oberheim OBX and this subject caused me a degree of 
head-scratching. At what point does "analogue character" step over the line 
and become a fault? I was hampered by the realisation that my own synth 
collection contains nothing but single-oscillator models, so I lacked 
hands-on experience!

There were two elements to it. First, there were minor timbral variations 
between voices even after they were all calibrated to the factory procedure. 
This would be more noticeable in some patches than others. I decided that 
this aspect (which affects single- as well as dual-oscillator synths) was 
unavoidable bearing in mind the nature of the OBX (early, largely discrete, 
with limited trimming facilities).

Then there is the matching between the oscillators on dual-osc machines. I 
think most people would want some slow phasing between the oscs on something 
like an OBX - none would be a bit sterile - but you want _the same amount_ 
on each voice. If the phasing rates are very different then this adds 
noticeably to the timbral variation. Generally one can do something about 
this, as tuning is trimmable. I did my best to match the eight voices, 
though I suspect that the road journey back to its owner will combine with 
the single-turn trimpots to reinject some additional "analogue character". 
Fortunately, that is what the owner says he appreciates in the OBX :-)

>But isn't this actually a normal situation to have certain amount of 
>polyphonic
>tonal disorder!?

IMHO it's just an aspect of what makes some people love analogue synths and 
other people want a better alternative, which is freely available in the 
form of...digital synths! At least nowadays one has the choice.

When playing chords, it just adds to the general swirl. It's when you play 
the same note repeatedly that it is most noticeable. The worst case is when 
the synth (as the OBX does)operates a strict 
step-sequentially-through-all-notes allocation policy, and this made me 
think that such a machine wouldn't be an ideal choice for a throbbing, 
mechanical bassline (for example). I had never considered that this might be 
a reason to choose a monosynth for those duties - alternatively, some polys 
offer a choice of voice allocation modes (e.g. the Roland Jupiter-4).

I for one continue to learn...

Steve L.