Re: Double precision

On 6/21/2013 11:19 PM, Ove Karlsen wrote:
> 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!

./configure --help did not list it.

Anyway I am compiling a windows binary ATM, and have looked at 
configMS.h also. I can´t see any mention of it. I also saw some various 
discussions in a search online, where doubles where criticised for 
speed. So I don´t know if that resulted in favorising 32bit code.

No one knows the code good enough to just know the variables that need 
resolution increase, to keep a double precision signalpath, and processing?

-- 
Ove Karlsen,
www.ovekarlsen.com


------------------------------------------------------------------------------
This SF.net email is sponsored by Windows:

Build for Windows Store.

http://p.sf.net/sfu/windows-dev2dev