From: Luke Koch <lu.ale.koch@gmail.com>
To: Muni Sekhar <munisekharrms@gmail.com>
Cc: alsa-devel <alsa-devel@alsa-project.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-sound@vger.kernel.org,
kernelnewbies <kernelnewbies@kernelnewbies.org>
Subject: Re: ALSA: arecord : silennce recorded as 0x80
Date: Fri, 14 Apr 2023 12:15:29 +0200 [thread overview]
Message-ID: <CAPDUAqPVDi4TgAja92tMqMp6rGAyC-eabS_6+W0zThKfsZAxGA@mail.gmail.com> (raw)
In-Reply-To: <CAHhAz+haVH-4Hgsz0PpTgUSW1pX4XxwxXwEd7nLVb0sFFwQwCg@mail.gmail.com>
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On Thu, Apr 13, 2023 at 3:50 PM Muni Sekhar <munisekharrms@gmail.com> wrote:
>
> Hi all,
>
> I recorded the silence on the default audio card by running "arecord
> -d 5 test.wav."
>
> Once it exited, I checked the contents by running "hexdump test.wav,"
> and I see that silence is recorded as a sequence of 0x80 instead of
> 0x00.
>
> 0000000 4952 4646 0024 8000 4157 4556 6d66 2074
> 0000010 0010 0000 0001 0001 1f40 0000 1f40 0000
> 0000020 0001 0008 6164 6174 0000 8000 8080 8080
> 0000030 8080 8080 8080 8080 8080 8080 8080 8080
> 0000040 8080 8080 8080 8080 8080 8080 8080 8080
> ...
>
> What might be the reason for silence being recorded as 0x80 instead of
0x0?
>
>
> --
> Thanks,
> Sekhar
This is what I found after Googling a bit:
Since you didn't specify a format, arecord defaults to 8 bit format (U8).
Being unsigned, a negative value for maximum negative amplitude is
impossible. Therefore the value is given a bias of 128,
making 0 the maximum negative amplitude, 255 the maximum positive, and 128
the center point (or silence).
Best Regards,
Luke
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prev parent reply other threads:[~2023-04-14 10:17 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-13 13:49 ALSA: arecord : silennce recorded as 0x80 Muni Sekhar
2023-04-14 10:15 ` Luke Koch [this message]
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