Re: [LAD] incorrect number of samples reading from /dev/dsp1

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To: farhan baluch <farhanbaluch@...>
Cc: <linux-audio-dev@...>
Date: Tuesday, February 1, 2011 - 10:37 am

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On Tue, Feb 1, 2011 at 7:55 AM, farhan baluch wrote:

> Hi All,

You need to use the correct ioctl()'s to set up the data format before you
read from the device. After you've done that, the data will make sense to
you. If you just start reading from the device, you don't know the sample
rate, bitdepth and channel count. I suspect the "duplication of data"
happens because the device is sending data in two channels. (mono in
"stereo")

Sampo

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On Tue, Feb 1, 2011 at 7:55 AM, farhan baluch <farhanbaluch@=
gmail.com
> wrote:
Hi All,=A0I am trying to read data from a usb microphon=
e and using the pretty standard method of using ioctl's to setup the sa=
mpling rate, channels, bits and block size . This all works so the device i=
s correctly setup. I then use "read" to read samples from the dev=
ice which shows up as /dev/dsp1. I get a lot more samples from this read co=
mmand in one second of recording than the set sample rate. E.g. if i set 10=
Khz on one run i got 269312 samples. Looking at the raw data it looks like =
there is a lot of duplication of data? is this common for the audio input d=
evice? if so what kind of encoding is it (e.g with some specific redundancy=
built in)?=A0
You need to use the correct ioctl()'s to set up t=
he data format before you read from the device. After you've done that,=
the data will make sense to you. If you just start reading from the device=
, you don't know the sample rate, bitdepth and channel count. I suspect=
the "duplication of data" happens because the device is sending =
data in two channels. (mono in "stereo")
=A0Sampo=A0

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Messages in current thread:
Re: [LAD] incorrect number of samples reading from /dev/dsp1, Sampo Savolainen, (Tue Feb 1, 10:37 am)
Re: [LAD] incorrect number of samples reading from /dev/dsp1, Gordon JC Pearce, (Tue Feb 1, 7:49 am)