From the original SynthMaker forum (2004–2014), with its members’ names and dates.
tor ·
Dont remember if i asked this once before. Sorry if i did. But, SM uses floating point... Is there any point in scaling the signal going into a biquad filter in a SM design considered the use of floating point precision? As I understandit is will not make any difference. But am I wrong here? See this article: http://www.bores.com/courses/intro/iir/5_scale.htm I guess the case in the article is a fixed system.
MichaelBenjamin ·
they are talking about integers - with floating point i would guess its still preferrable to stay in -1/1 since float resolution is not equally spaced. you could try to add dc of say 500 000 and hear if it makes a difference.
trogluddite ·
MichaelBenjamin wrote: add dc of say 500 000 and hear if it makes a difference.
Adding a large fixed number will reduce the resolution, as you would be confining the original +1/-1 to fewer bits in the mantissa of the float number. The bigger the number you add, the lower the resolution of the smaller part that you are interested in. As a simple analogy, imagine I have a calculator that can only show 8 digits. The decimal point can be shown at any place across the screen - so it is a sinple form of 'floating point' maths.
so.. 4.5 + 3.0002 =7.5002 No problem, the decimal place moved further left, and we can still see the whole result. But... 10000000 + 3.0002 =10000003 Or 0.0000001 / 10 = 0.0000000
Something is lost with these examples because there are no more digits left or the decimal point couldn't move any further. Float numbers work very much like this - there are 23 bits representing the 'digits' (matissa) and 8 bits representing the 'position of the decimal point' (exponent), plus a sign bit for +/-.
Scaling (multiplying) your input wouldn't alter the precision (same number of digits), but might allow a feedback loop to go on longer before the numbers got too small (run out of decimal places). But in practice those numbers are so small, that a soundcard could never represent them anyway.
The Wiki article about IEEE754 has a few useful explanations and tables about the limitations of float numbers.
tor ·
Thank you for the nice refreshing explanation and examples Trog. Some times i just start to doubt what i earlier have learned. You have the abilty to explain things so even my mother could understand. Are you or have you concidered becoming a teacher? 🙂
trogluddite ·
tor wrote: explain things so even my mother could understand.
He he, I do provide a kind of '24hr telephone tech. support' for my mother, she decided to become a 'silver surfer' when she retired. Thanks for the compliment 🙂 doing the little examples often reminds me of things that I had forgotten.
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