24. audio: Handling Voice with ISDN

(Most of the answers you will find here are taken from the - now unfortunately outdated - vbox manual by Matthias Hessler hessler@isdn4linux.de and Bernhard Hailer dl4mhk@lrz.uni-muenchen.de; you can get the manual at:

http://www.lrz-muenchen.de/~ui161ab/www/isdn/

- click on "Audio!" (still in German we're afraid - sorry...) They are currently very outdated, but may give you a few hints?

A newer place has now come up as a place for further vbox development. Please check it out: http://innominate.org/projects/vbox/index.php3

24.1 audio_links: Where can I find helpful links regarding vbox?

There are several scripts available to be used in connection to vbox, but the author is not up to date. Here is the latest one I received information about: http://innominate.org/projects/vbox/index.php3 Please send me information if you know more helpful links, or howtos, or whatever useful...

Also please note the documentation in the kernel source package: /usr/src/linux/Documentation/isdn/README.audio

24.2 audio_format: What is the format of the audio messages (.msg) vbox plays when it answers a call?

You can get the format from the messages with rmdgetheader. The samples messages in the packages are recorded using format 4 (the latest Zyxel-Compression)

24.3 audio_recordmsg: How can I record my own messages for vboxgetty?

First call yourself on the number you configured vboxgetty to answer and leave a message. Then rename the message to *.msg (standard.msg for the main answering message) and copy it to the directory where all the messages are kept (usually /var/spool/vbox/user/messages where user is the user for which vboxgetty is configured). You can also record a message using a microphone and the soundcard.

24.4 audio_play: How can I play audio messages locally using /dev/audio?

This is best achieved with vbox using format 6 (uLaw - must be compiled in). You can then easily play the messages using:

cat xxx  /dev/audio

24.5 audio_convertto: How can I convert audio messages which where recorded by vbox to other formats (i.e. from uLaw to WAV)?

The standard tool for converting all sound formats is SOX. SOX is available as source code for both UNIX and DOS. You can get it at:

http://www.powerweb.de/mpeg/util/msdos/sox10c.zip

(including sources that compile under Linux).

24.6 audio_convertfrom: How can I format WAV for uLaw (for my vbox announcement message)?

We receive the following tip form Christian Stueble stueble@ls6.informatik.uni-dortmund.de on 15 Jan 1997:

For me, the following (somewhat indirect) method works:

sox file.wav -r 8000 file.ul rate
rmdcatheader -u file.ul  file.msg
cat file.ul  file.msg

24.7 audio_dtmf: How can I improve the recognition of (DTMF) dial tones?

You can adjust the parameters DTMF_TRESH, SILENCE_TRESH, and H2_TRESH in file linux/drivers/isdn/isdn_audio.c. A DTMF tone is recognized if the amplitude of the correct frequency is larger than DTMF_TRESH and the amplitude of the second harmonian frequency is smaller than H2_TRESH. If a dial tone is recognized when no dialing took place, try to increase DTMF_TRESH and/or decrease H2_TRESH. However, test with many telephones - the current parameters were already set after some tuning.

24.8 audio_e0265: My vboxgetty gets a modem timeout, and reports error E0265.

Probably you need a patch that has been posted recently (8th December 1999) on the mailing list.

24.9 audio_noanswer: My vboxgetty does not answer any incoming calls.

vboxgetty needs ".vboxrc" in the home directory of the user for which vboxgetty is configured. The number of rings is taken from this file.

24.10 audio_nocat: If vboxgetty has recorded a message in a format which can not be played using "cat xxx/dev/audio" how can I still hear the message?

Vboxgetty can play all formats. You can copy the message as the standard message (standard.msg in the messages directory) and call yourself, the message will be played then. (Don't forget to copy back the original message when you are done :-) ). See question audio_recordmsg.

24.11 audio_earlyrecording: At the beginning of a message recorded by vboxgetty, there's often a part of my own announcement?

This is a known bug that occurs when switching between the playing of the announcement and recording the message. Up to now there is no known workaround.