Good designs of Expo Converters? Was: [sdiy] Multiplexed Expo Converter?

[Scott Nordlund]

The Evolver seems to use exponential FM on its digital oscillators (cross-coupled, no less).  It's difficult to get anything but dissonance and/or chaos out of it.  This has its place, of course, but linear FM can easily achieve dissonance and inharmonicity as well.

I'm familiar with phase modulation, as that's how digital "FM" synths are implemented.  I guess this same method could be sort of achieved in the analog domain, but it doesn't seem like a fantastic idea to me.

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> Date: Sat, 1 Aug 2009 17:38:06 +0100
> Subject: Good designs of Expo Converters? Was: [sdiy] Multiplexed Expo Converter?
> From: cheater00 at gmail.com
> To: synth-diy at dropmix.xs4all.nl
>
> Scott,
> thanks for your answer. I didn't know expo FM was inharmonic, I'll
> need to check that stuff out, it sounds really neat actually -
> inharmonicity is one thing you can use to make sounds much more
> interesting. On another note, PM is sort of like FM but not - it's
> very fun - check it out if you ever get a chance. Patch something
> across an accumulator cap or something (it would be more involved than
> that to get real Phase Modulation but might give you some form of
> foretaste)
>
> Guys, what are some good designs of Expo Converters?
>
> Cheers
> Damian
>
> On Fri, Jul 31, 2009 at 8:08 PM, Scott Nordlund wrote:
>>
>>> 1. FM
>>> I thought 'linear' audio rate FM was supposed to be much better. What
>>> can you guys tell me about expo vs linear fm? I have seen some VCOs
>>> with 'linear fm in', I guess that just bypasses the EC?
>>>
>>> Or is 'linear' audio rate FM better for the specific reason that
>>> removing the EC makes the system simpler and hence easier to make very
>>> good?
>>
>> Exponential FM is inharmonic, so it's generally less musically useful.
>>
>>> 2. PM
>>> Correct me if I'm wrong, but I think PM again doesn't need an EC, does
>>> it? Even if it's DC modulation...
>>
>> Analog phase modulation is used sometimes for radio signals, but I don't if or how it could be implemented for musical purposes (I can't think of any examples, phase shifters aside).
>>
>>> 3. AM/RM
>>> I don't think AM needs EC.. at all... correct me if I'm wrong, please.
>>
>> You could run the two input signals through exponential converters, sum them, then run that through a logarithm...
>>
>>
>>
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