Re: [Audacity-devel] Amplify is very noisy

[Gordon W. <gor...@ch...>]

Leland,

I just tried the same experiment on Linux.  With float, generated
silence is truely 0 with no noise at all.  No amount of amplification
gives any noise.

Export this to wav, and reload it.  Now max amplify twice gives
full scale noise.  This is the dither that's added during the
conversion to 16 bit before the export.  The dither code is deep
down in the format conversion macros.

With a 16 bit audio board, the dither really isn't needed because
the hardware has more noise than the dither is adding.  The dither
is there to hide the quantization noise.

Gordon Weast



Leland wrote:
> --On June 3, 2008 12:06:26 AM +0100 Martyn Shaw 
> <mar...@go...> wrote:
>
>   
>> Hi Leland
>>
>> OK, so I know you claim to have no knowledge of signal processing, but
>> this is above the level of 'trivial', so I forgive you!
>>
>>     
> :-)
>
>
>   
>> Now how did those values get there?  I deduce that your track is in
>> 16-bit PCM mode before generating silence.  Also that you have the
>> default 'shaped' pref set in the Quality pref for dither.
>>
>>     
> Yep, and yep.  Changing to float does not produce the "noise".
>
>   
>> You don't want to get into the maths of this!
>>
>>     
> Ahhh...  :-)
>
>   
>> This isn't a 'problem', it's by design.  It shouldn't go on any list
>> of problems.
>>
>>     
> Good, cause I wasn't looking forward to it.
>
> Thanks a heap!
>
> Leland
>
>
> -------------------------------------------------------------------------
> This SF.net email is sponsored by: Microsoft
> Defy all challenges. Microsoft(R) Visual Studio 2008.
> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/
> _______________________________________________
> Audacity-devel mailing list
> Aud...@li...
> https://lists.sourceforge.net/lists/listinfo/audacity-devel
>
>