num/denom v's double (was: Re: [LAD] [ANN] LV2 beta3)

Steve Harris steve at
Sat May 12 19:34:43 UTC 2007

On 12 May 2007, at 05:52, Dave Robillard wrote:

> On Fri, 2007-05-11 at 18:24 +0100, Steve Harris wrote:
>> On 11 May 2007, at 15:07, Fons Adriaensen wrote:
>>> On Fri, May 11, 2007 at 03:33:04PM +0200, Lars Luthman wrote:
>>>> That sounds like a good argument for two ints to me. Although
>>>> you'd have
>>>> to do a lot better than double if you wanted to represent  
>>>> irrational
>>>> numbers in binary form. =)
>>> Two 32-bit ints can represent (the non-integer part of) most (not  
>>> all)
>>> irrational values to better precision than a double. The algo to  
>>> find
>>> them is a bit mysterious but very simple. Simple example: 355/113 is
>>> equal to pi with a relative error of less than 1e-7, not bad for two
>>> 3-digit numbers. It's not difficult to find two 32-bit ints that  
>>> would
>>> be better than a double.
> [snip]
>> My preference is still to go for a double, as the difference is too
>> minimal to be audible, under any circumstances, and it makes plugin
>> developers lives harder.
> The annoyance on the plugin developer is small enough that I don't  
> think
> it sways the decision very much.

You might feel differently if you had 100 run methods to change, but  

> I'm all for LV2 being minimal, since extensions can take care of
> additional functionality and everything will just work out all nice  
> and
> open sourcey; but deliberately putting things in the spec that's known
> to be less able than a (not that much more complicated) alternative
> really doesn't sit right with me.


> A single division doesn't justify crippling the spec if there's any  
> even
> remotely feasible application of the numerator/demoninator method,  
> IMO.
>> LV2 is intended to be an audio plugin
>> format, not for scientific uses. Of course if the host gets its
>> sample rate as a double, it's a PITA, and generally lossy to convert
>> that into num/denom.
> This, OTOH, would sway the decision more than the division, if it were
> actually a problem (though being a host and not plugin nuisance  
> weakens
> the relevance quite a bit).  It's not a problem on any of the (typical
> 'round these parts) audio APIs I know.. is it a problem anywhere  
> LV2 is
> ever likely to see the light of day?

No idea.

- Steve

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