[sdiy] Taylor series and sums and difference tones

[Dave Manley]

Aaron Lanterman wrote:
> On Jun 5, 2009, at 1:36 AM, Dave Manley wrote:
>
>> On a related note, Grant Richter has commented that for the best 
>> sounding multiplication (as in a balanced modulator), you want the 
>> sine to be very pure, because any components that are not the 
>> fundamental will result in, to use Aaron's terms, "all sorts of 
>> junk".  Of course, it depends on how many dB down the stray 
>> components are.  A sine from a self-oscillating filter is better than 
>> any sine from a shaper for use in multiplication for this reason.
>
> I remember Grant suggesting one that uses the weird properties of an 
> incandescent light bulb. (I believe it was the Hewlett-Packard design.)
>
I must have missed that comment, but can believe it - from Wikipedia 'RC 
Oscillator': "Many common designs simply use an incandescent lamp 
<http://en.wikipedia.org/wiki/Incandescent_lamp> or a thermistor 
<http://en.wikipedia.org/wiki/Thermistor> in the feedback circuit. These 
oscillators take advantage of the fact that the resistance 
<http://en.wikipedia.org/wiki/Electrical_resistance> of the tungsten 
<http://en.wikipedia.org/wiki/Tungsten> filament 
<http://en.wikipedia.org/wiki/Electrical_filament> of the lamp increases 
in proportion to its temperature 
<http://en.wikipedia.org/wiki/Temperature>, a thermistor 
<http://en.wikipedia.org/wiki/Thermistor> works in a similar fashion. 
Operated well below the point at which the filament actually 
illuminates, increased amplitude of the feedback signal causes increased 
current flow in the filament thereby increasing the resistance of the 
filament. The increased resistance of the filament reduces the feedback 
signal, limiting the oscillator's signal to the linear range 
<http://en.wikipedia.org/wiki/Linear_range>. (That is, clipping 
<http://en.wikipedia.org/wiki/Clipping> is prevented.) The HP 200 
oscillator introduced this technique."

-Dave