Re: Double precision

On Fri, 21 Jun 2013 15:22:58 +0200
Thomas Orgis <[email protected]> wrote:

> Am Thu, 20 Jun 2013 18:31:58 +0200
> schrieb Ove Karlsen <[email protected]>: 
> 
> > Does anyone know if increasing internal resolution in lame encoder
> > would be trivial? I thought in 2013, it might be nice to increase
> > that to double.
> 
> Well, in 2013 you'd rather port the single precision code to run on
> GPUs;-)
> 
> But really, is there any hint that double precision would help
> anything with MP3 quality? Even for studio productions, I only see 32
> bit float PCM as top-notch format. Would using double precision for
> intermediate calculations really make any difference on a resulting
> bitstream? I'm not even talking about audible differences.

I remember that we had a switch in the code which changed from float to
double. I don't remember if we removed it at some point or if we still
have it. IIRC we also had an option for in the unix configure script
for this.

In general the difference between IEEE float and IEEE double _can_ make
a huge difference in the precision in the numbers if you just look at
the values. To understand it correctly you would have to learn about
the corresponding IEEE standard. In short (and exagerated): if you are
unlucky a simple integer value X would be represented in float as
(X-1).9 or some similar floating point value around the real value. For
double values the difference between the real value and the represented
value in memory is smaller. This starts to matter when you do a lot of
calculations (specially multiplications or divisions) with those
values, the "error" can accumulate to a big value.

Now... for the audible difference... well, the whole concept of MP3 is
to rely on the fact that the ear does not hear at all deviations from
the original.

Bye,
Alexander.

-- 
http://www.Leidinger.net    Alexander @ Leidinger.net: PGP ID = B0063FE7
http://www.FreeBSD.org       netchild @ FreeBSD.org  : PGP ID = 72077137

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