Re: Double precision

On 6/21/2013 10:36 PM, Alexander Leidinger wrote:
> 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.
That would be excellent. I am going to look for it then.
>
> 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.
Only on simple IIRs the difference can be heard. It might take a 
high-end D/A though (multibit).
>
> 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.
Yes. I do still think that internal resolution should be double though.
>
> Bye,
> Alexander.
>
Peace Be With You!

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