Re: [LAD] Tutorial for programming with JACK

I updated the sources.

One question. In jcapture, I printf the meter in the console with vertical bars '|' as usual. I calculate an average from 5 callback calls, and I printf the meter inside the callback functions, that is not real safe. Where to printf the meter? Must be inside the infinite loop for(;;)... this way is real safe?

Joan Quintana

--- On Fri, 2/24/12, Robin Gareus <robin@email-addr-hidden> wrote:

From: Robin Gareus <robin@email-addr-hidden>
Subject: Re: [LAD] Tutorial for programming with JACK
To: "Joan Quintana" <joan_quintana@email-addr-hidden>
Cc: Linux-audio-dev@email-addr-hidden, "Harry Van Haaren" <harryhaaren@email-addr-hiddenmail.com>
Date: Friday, February 24, 2012, 5:07 PM

Hi Joan,

Thanks for sharing those!

On 02/24/2012 11:12 AM, Joan Quintana wrote:
> Related with this topic, I would like to contribute with 3 pieces of code made with an educational point of view (though I don't teach audio processing and I don't consider an expert myself). These examples use libsndfile library, that is important if the source or the destination of your audio data is a wav file.
>
> a) jcapture:
> *http://wiki.joanillo.org/images/0/07/Jcapture-1.0.0.tar.gz
> reads the data coming from the microphone, and saves a wav file. Shows a textual signal meter in the console. (I know the existance of jack-capture. I didn't look at jack-capture code, sure that has better performance and lots of options, I just wanted the minimal code)

The linked tar-ball includes jcapture-0.0.1.cpp that does not save any
.wav file.

Calling printf() in the jack-callback function is not realtime safe;
[but it's perfectly valid for debugging/development purposes and] I
guess you simply mixed up the files.

FWIW
https://github.com/jackaudio/example-clients/blob/master/capture_client.c
is very close to the minimal code required to do disk I/O. It does not
include a meter, but supports multiple-channel.

> b) jplay-sndfile-simple:
> *http://wiki.joanillo.org/images/1/1e/Jplay-sndfile-simple-1.0.0.tar.gz
> It's just a playback wav file. In the callback function there are two possibilities: copying blocks of memory; or copying sample by sample, and this permits a little signal processing (in this simple case just divide the signal by 2).
> I borrowed code from sndfile-jackplay.c (sndfile-tools-1.03, Erik de Castro Lopo & Jonatan Liljedahl), where is interesting the thread implementation  (playing while reading the file) that I didn't implemented.

neat. There's some cruft in it (unused variables, binary (&) vs boolean
(&&) AND in line 89) - compile with `-Wall` option: g++ will tell you.

Otherwise it'd make a nice addition to
https://github.com/harryhaaren/Linux-Audio-Programming-Documentation

> c) jplay-sndfile:
> *http://wiki.joanillo.org/images/e/e6/Jplay-sndfile-1.0.0.tar.gz
> This is more interesting and not simple like the previous. A part of playing back the file, it permits frequency shifting and frequency sweeping in a range between .5 and 2.

see previous email (reply to Harry).

> Hope this helps to somebody,
> Joan Quintana
>
>

best,
robin

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Received on Mon Feb 27 04:15:01 2012