[sdiy] Analysis of frequency variation in analogue synths

[Dave Kendall]

I wonder if the so-called "warmer" sound of VCOs vs. DCOs, may be at 
least in part, that when mixed into a  piece of music with other 
recorded sounds, a typical VCO's  instability can produce beat  
frequencies that many find pleasing to the ear ?

Thus the effect only *really* shows up in a composition, and refuses to 
show itself when isolated.

I remember a track I once worked on, where the interplay between a 
chorused guitar and a K2000 arpeggiated sequence mixed together, 
produced the discernable effect of a tone a 5th above the root key 
shifting to a 6th above and back again, in time with the beat.
The singer originally pointed it out, and for a while we all wondered 
what was in her tea...., but after the rest of the instruments were 
faded down, indeed everyone heard it......

Dave

Anyone fancy a deep-fried worm?  :-)





On 3 May 2007, at 10:41, Tom Wiltshire wrote:

> Hello All,
>
>
>
>>> I realize its been debated a lot, and I don't think Tom or I was
>>> trying to heat the debate.
>
> Sorry if anyone feels like I took the lid off the wormcan when we'd 
> only just managed to force it back on!
>
>>> What we both seem to be after is finding
>>> the conclusive evidence you mention.
>
> Absolutely.
>
>> Conclusive evidence is hard. Not only do you need to measure various 
>> sources
>> for a number of suspected effects (AM, PM, Moon phase or whatever), 
>> but you
>> need to measure them well enought from a large number of sources and 
>> then have
>> them blind-tested on a large enought scale of people that know 
>> whatever
>> psycho-acoustical sensation(s) you are after and is able to rate that 
>> sensation
>> for each of the test objects. This part of the test also needs about 
>> the same
>> signal or else the test subjects have too easy to spot a Moog from an 
>> ARP or
>> whatever. Thus the blindness needs to be fairly complete. Only after 
>> analyzing
>> this and seeing correlations between the test-persons judgement and 
>> some of
>> the measures you made on the source, you are approaching conclusive 
>> evidence.
>> You can naturally convince yourself by reducing the test-person to 
>> yourself,
>> but you must recall that you don't have conclusive evidence that will 
>> count
>> with everyone. The experiment I presented above would also have to be 
>> repeated
>> by independent groups and come to similar enought conclusions for it 
>> to attempt
>> to be conclusive. It also needs to be published in a good enought 
>> journal with
>> sufficient review to start to count as evidence. This is how the 
>> scientific
>> community works. Everything else we do is interesting exercises. 
>> Those can be
>> made more or less skillfull.
>
> For myself, before I can think about the next step of whether a 
> certain type of error or drift is associated reliably with 'the 
> analogue sound' or the 'moog sound' or 'arp sound' or whatever, I need 
> to see some measurable effect, which I haven't managed to do reliably.
> Although I've heard much heated debate about VCOs being better than 
> DCOs (or not) and many presentations of the reasons that this might 
> (or might not) be the case, there isn't a great deal (notice I'm not 
> saying none) of actual experimental data showing measurable 
> differences. What does the frequency/phase drift on a VCO look like? 
> Show me a trace! How much comparator jitter is there on a Moog VCO? 
> Give a percentage! Unless I can measure and identify these effects, I 
> don't stand a chance of trying to emulate them in a digital 
> oscillator, which is my ultimate motivation for all this.
>
> Given that a bench frequency generator, a Moog modular, an ARP 
> odyssey, and a Prophet 5 can all generate a ramp wave of a given 
> frequency (say, concert A 440Hz for the sake of argument) and some 
> aficionados would claim that all of these sources have a different 
> character (and I'm quite prepared to believe that they do) then what 
> are differences between them? What aspects of the waveshape? What 
> variations of time? Which parameters? Once we know that, we can start 
> trying to work out which of those factors are significant to the 
> individual sounds and do the sort of "Is it a Moog or a fake?" 
> double-blind trials that would turn it into a serious scientific paper 
> (if anyone felt the need!).
>
> Magnus clearly has much more experience and equipment for measuring 
> these things that I do, and it may be that the CD quality sampling 
> that I was using to get data is insufficiently accurate to find any 
> useful effects. However, even if I were able to show that this were 
> the case, that in itself would be an interesting result for a digital 
> oscillator design.
>
> If none of that works - do Rentokill deal with escaped worms?!
>
> Tom
>
>
>
>
>
>
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