[LAU] Record levels lower in Alsa than Jack

[John Murphy]

On Fri, 6 Nov 2020 20:19:02 -0500 "Tim E. Real" wrote:

> On 11/6/20 10:06 AM, John Murphy wrote:
> > On Fri, 6 Nov 2020 15:07:43 +0100 Fons Adriaensen wrote:  
> >> On Fri, Nov 06, 2020 at 01:22:42PM +0000, John Murphy wrote:
> >>  
> >>> Then sox stat shows min/max amplitude +/- 0.5 for the wav capture and
> >>> +/- 0.9 for the wav converted from w64. The converted file looks good
> >>> in my editor too.  
> >> Still doesn't explain the difference, unless I'm missing something...
> >>  
> > There's a loss of precision in the conversion process. Both the original
> > recordings show 25 bit precision and the file sizes are the same (3.8MB).
> >
> > The converted file is only 16 bit and is 1.9MB. It sounds (and looks)
> > louder. I doubt I could tell any loss of quality. Not explaining it.
> > Just providing some facts. :)
> >  
> Maybe this is relevant?
> 
> According to my package manager, sox depends on libsndfile.
> 
> On the libsndfile website: 
> http://www.mega-nerd.com/libsndfile/api.html#note1
> 
>   it talks about normalization:
> 
> 
> "When converting between integer data and floating point data, different 
> rules apply.
> 
> The default behaviour when reading floating point data (sf_read_float() 
> or sf_read_double ())
> 
>    from a file with integer data is normalisation. Regardless of whether 
> data in the file
> 
>    is 8, 16, 24 or 32 bit wide, the data will be read as floating point 
> data in the range [-1.0, 1.0].
> 
> Similarly, data in the range [-1.0, 1.0] will be written to an integer 
> PCM file so that
> 
>   a data value of 1.0 will be the largest allowable integer for the 
> given bit width.
> 
> This normalisation can be turned on or off using the sf_command 
> <http://www.mega-nerd.com/libsndfile/command.html> interface"
> 
> 
> I recall observing that this normalization does tend to make the result 
> 'louder'.
> 
> Could this be what is being observed?

That would seem to explain it and the output of sndfile-info appears
to confirm (see my reply to Chris). Quite surprised it does that extra
thing for me.

Thanks all.

-- 
Thanks again,
John.