[LAU] Record levels lower in Alsa than Jack

Tim E. Real termtech at rogers.com
Sat Nov 7 02:19:02 CET 2020

On 11/6/20 10:06 AM, John Murphy wrote:
> On Fri, 6 Nov 2020 15:07:43 +0100 Fons Adriaensen <fons at linuxaudio.org> 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: 

  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 

Could this be what is being observed?


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