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Originally Posted by

**editronmaximon**
That's not what you say in your earlier incorrect statement.

My statement was incomplete in its description. I guess I thought that having dealt with these sorts of number for nearly three decades I didn't need to expect someone who's read a couple of things on the web trying to find fault.

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That's not true, unless you are perhaps limiting your analysis to certain cases where it may be.

In particular, there are numbers that can be represented in fixed point that cannot be represented at all in floating point.

Not if the mantissa is of the same length as the fixed point representation.

It's easy enough to show, if we use fixed and floating point decimal (the principle is exactly the same, but the numbers make more sense to us as humans).

If we have fixed point with two digits of precision, it can represent any two digit value...

10

56

23

11

etc.

Floating point with the same precision of mantissa can also represent any of those numbers, it can also represent shifted versions of them

so not only can it perfectly represent

10, 56, 23, 11 etc,

but it can also perfectly represent

100000, 5.6, 0.0023, etc.

Now of course we need to store that shift, which is the exponent, so let's say we use one digit for that, giving us an effective exponent of -5 to +4

So the floating point representation takes up three digits of space, versus the fixed point one which is using two... so what if we make the fixed point one three digits?

Well then for a range of numbers the fixed point has the advantage, it can represent values between 100 and 1000 more accurately

123

456

874

etc, the best the equivalent size of float could do is

120

460

870

But anything below 10 it represents less accuratly, and it can't represent anything over 999 at all, so it's more accurate in some cases, and worse in others.

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As it turns out, writing dsp code does not require a complete understanding. You have tools to work with where others have done the deep work.

You haven't the first clue about what I do, so don't pretend you do.

I program at the "deep" level, and in the past I've jumped through hoops and done various mathematical tricks to extract the last bit of precision out of a fixed point algorithm (hand coded in assembler) in order to give maximum quality on something with very limited processing power.

So stick to **** you know something about, this isn't it.

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That's pretty funny.

Yeah, hilarious, that I should consider it even vaguely possible to educate you.

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I have enough understanding to know that you don't.

Q.E.D.

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One clue for others may be the fact that your homebrew theories are often in complete opposition to what respected authorities say. Too much spin and agenda from you.

Actually generally speaking they're not, just contrary to your limited understanding of what the "respected authorities" say.

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I've been at this for a long time, and I know how to discern reliable information.

Nope, sorry, that's a fail on that one.

It's not enough for the source to be reliable, and you're not even good at that, you also need to understand the information provided, and you regularly get that wrong.

But there are people here who can benefit, even if you're too obtuse to, so I'll keep posting to help them... and if that means I correct you, then so be it.