ALSA Questions - MUTE and PLAYBACK RATE

ALSA Questions - MUTE and PLAYBACK RATE

[Xavi Alexis]

Hello ALSA people,

How do you use the ALSA API to mute the MICROPHONE?

How do you use the ALSA API to mute the SPEAKER?

How do you reduce the playback latency or delay? I am reading my audio and I 
notice that there is a delay ... or some kind of latency. I want the audio 
played as soon as it is read or something close to that.

Thanks,
X

Re: ALSA Questions - MUTE and PLAYBACK RATE

[Clemens Ladisch]

Xavi Alexis wrote:
> How do you use the ALSA API to mute the MICROPHONE?
> How do you use the ALSA API to mute the SPEAKER?

These questions assume that "the MICROPHONE" and "the SPEAKER" actually
exist.  However, there are cards that have none, or more than one, or
that cannot be muted, or where the muting isn't controllable by
software.

In the general case, these settings should be controlled by the user
with a mixer application.

What are you trying to do?

> How do you reduce the playback latency or delay?

Reduce the buffer size.  However, this increases the danger of buffer
overruns.

You need low latency only when you are generating sounds in real time in
response to external events.

> I want the audio played as soon as it is read or something close to that.

Does "read" mean "read from disk" or "capture"?


Regards,
Clemens

Re: ALSA Questions - MUTE and PLAYBACK RATE

[Xavi Alexis]

Thank you Clemens for your answers:

A few more questions:

What is the SPECIFIC function to reduce the BUFFER size?

When I say read ... I am reading the data over a socket ... 

Thanks again.

x




________________________________
From: Clemens Ladisch <clemens@ladisch.de>
To: Xavi Alexis <xamalek@yahoo.com>
Cc: alsa-devel@alsa-project.org
Sent: Thu, October 21, 2010 5:39:46 AM
Subject: Re: [alsa-devel] ALSA Questions - MUTE and PLAYBACK RATE

Xavi Alexis wrote:
> How do you use the ALSA API to mute the MICROPHONE?
> How do you use the ALSA API to mute the SPEAKER?

These questions assume that "the MICROPHONE" and "the SPEAKER" actually
exist.  However, there are cards that have none, or more than one, or
that cannot be muted, or where the muting isn't controllable by
software.

In the general case, these settings should be controlled by the user
with a mixer application.

What are you trying to do?

> How do you reduce the playback latency or delay?

Reduce the buffer size.  However, this increases the danger of buffer
overruns.

You need low latency only when you are generating sounds in real time in
response to external events.

> I want the audio played as soon as it is read or something close to that.

Does "read" mean "read from disk" or "capture"?


Regards,
Clemens
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Re: ALSA Questions - MUTE and PLAYBACK RATE

[Clemens Ladisch]

Xavi Alexis wrote:
> What is the SPECIFIC function to reduce the BUFFER size?

The buffer size (or the equivalent time) is a parameter to the
snd_pcm_set_params() or one of the snd_pcm_hw_params_set_buffer_*
functions.


Regards,
Clemens