posted 13 February 2001 00:03            

quote:

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Originally posted by JohnCowan:
The minimum value in the VCS editor changes into this strange number when I change the taper from linear to log. If I type in 0 and hit enter in the minimum field, the odd number reappears. There seems to be no way to change it.

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There is no "zero" on a log scale unless you can handle an exponent of negative infinity, which most computers can't. That "strange" number Kyma puts in is simply the closest thing to zero your computer can calculate.

posted 13 February 2001 05:21            

quote:

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Originally posted by JohnCowan:
I created a volume fader ... changed the taper from linear to log. The min ... 2.384...d-7. It does not ... 0. Am I missing something?

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Dear John,

What does this number tell you?
I can understand this: How zero is 0 on a computer? It depends on the representation of the numbers. Keep in mind
2.384...d-7 is a very small number (-132dB (amp) or -66dB (Power)!

In case you chose log taper, the faders absolute position is mapped onto a exponential function (little bit confusing log taper = exponential function).
Why exponential: If you move your fader on the top of the scale (say 1/8 from top) the value changes quiet fast from 1.0 to 0.5. All what is left of the fader size (7/8) is used to get the value from 0.5 to almost zero. Look in Math book with exponential function drawings.

Notation: 2^x = 2 to the power x
To come back to mapping: The fader positions is actual stored in 24 bits(motorola processors use 24 bits to store numbers within the range [-1.0...1.0> ). The fader pos. only uses part of the range [0...0.5]. For a linear mapping (lin taper, min 0, max 1) we just multiply the fader pos. by 2. Actually there is almost no operation involved, the bits are shifted one position to the left. For log taper however SSC had to decide how to map these fixed fader pos. to an interesting exponential function. In computer world it is always simpler to calculate with powers of 2, so also SSC does this. They took the 2 to power of exponential function.
By doing some tricks like counting the numbers of ones in the 24 bit word of the faders pos. they convert it into a 2power scale. When the fader is in his max. position we get 2^0 = 1. When the fader is in his lowest position we get 2^-22= 2.384185791E-7! So this is not a BUG! SSC did I miss here something? I am reverse enginering your work now.

I hope you get it!
Although (I think) what you wanted to do was just make a volume fader as on a mixing desk?
Another more logical way to do this:
Define a linear fader("!MixAmp") with min -100 and max 0! In the fields where you use this "!MixAmp" place dB behind it.
Again the values (in linear domain), do not reach 0.0 but also a mixing desk fader doesn't do that! -100 dB is more then enough attenuation for a 16 bit signal with only 96 dB Signal/Noise. You could also use -144 (=24*-6) as a minimum if you think you have such good quality equipment.

posted 13 February 2001 05:25            

-Christiaan