Re: [Alsa-user] S32_LE format

[John S. <lin...@fr...>]

John Sigler wrote:

> I experimented with the following command:
> 
> $ arecord -vv -M -r 48000 -f S32_LE -t raw -d 60 -D hw /tmp/out
> 
> which gave the following output:
> 
> Recording raw data '/tmp/out' : Signed 32 bit Little Endian, Rate 48000 
> Hz, Mono
> Hardware PCM card 0 'HDSPM MADI' device 0 subdevice 0
> Its setup is:
>   stream       : CAPTURE
>   access       : MMAP_NONINTERLEAVED
>   format       : S32_LE
>   subformat    : STD
>   channels     : 1
>   rate         : 48000
>   exact rate   : 48000 (48000/1)
>   msbits       : 24
>   buffer_size  : 8192
>   period_size  : 4096
>   period_time  : 85333
>   tstamp_mode  : NONE
>   period_step  : 1
>   avail_min    : 4096
>   start_threshold  : 1
>   stop_threshold   : 8192
>   silence_threshold: 0
>   silence_size : 0
>   boundary     : 1073741824
> 
> AFAIU, S32_LE means that each sample is a 32-bit signed quantity stored 
> least-significant byte first, right?
> 
> e.g. -2 (0xfffffffe) is stored as "fe ff ff ff" and 1 is stored as
> "01 00 00 00" right?
> 
> The dump of the beginning /tmp/out follows:
> 
> 00000000  00 00 a5 f5 08 00 43 f6  08 00 bc f6 00 00 20 f7
> 00000010  08 00 9a f7 00 00 3e f8  00 00 11 f9 08 00 f2 f9
> 00000020  00 00 a9 fa 08 00 42 fb  08 00 e7 fb 08 00 6b fc
> 00000030  08 00 ae fc 00 00 f6 fc  00 00 75 fd 08 00 f3 fd
> 00000040  00 00 31 fe 08 00 41 fe  00 00 62 fe 00 00 b5 fe
> 00000050  00 00 30 ff 08 00 c2 ff  00 00 47 00 08 00 80 00
> 00000060  00 00 65 00 00 00 47 00  00 00 63 00 08 00 ab 00
> 00000070  00 00 f9 00 08 00 0c 01  08 00 c4 00 00 00 60 00
> 00000080  08 00 1a 00 00 00 c3 ff  00 00 2d ff 08 00 7e fe
> 00000090  00 00 d5 fd 00 00 2f fd  00 00 95 fc 00 00 03 fc
> 000000a0  08 00 66 fb 00 00 d7 fa  08 00 6b fa 08 00 01 fa
> 000000b0  08 00 91 f9 00 00 41 f9  00 00 e9 f8 08 00 4e f8
> 000000c0  00 00 c4 f7 00 00 89 f7  00 00 2a f7 08 00 43 f6
> 000000d0  08 00 f9 f4 00 00 81 f3  08 00 0f f2 08 00 ce f0
> 000000e0  08 00 81 ef 08 00 08 ee  08 00 b2 ec 00 00 7e eb
> 000000f0  08 00 27 ea 00 00 d4 e8  00 00 bd e7 00 00 b6 e6
> 
> The first sample is stored as 00 00 a5 f5.
> Does this represent the value 0xf5a50000?
> 
> For the majority of samples, the first two bytes are 00 00.
> Is this because the input stream was, in fact, a 16-bit stream?
> 
> For the rest of the samples, the first two byte are 08 00.
> Why don't all the samples start with 00 00?
> Does this sequence 08 00 have a special meaning?

Would anyone care to venture a guess?

Regards.