Setting up soundmodem on Ubuntu 10.04

June 29, 2011

After a long delay, I finally decided to upgrade to 10.04 LTS and get soundmodem running again.

Luckily, there was help this time. I started with my config, and merged with this post:
ubuntuforums.org/showthread.php?p=10864691

Here’s the config I ended up using:

Configuration: AX.25
IO:
Mode: soundcard
Audio Driver: /dev/dsp
Half Duplex: selected
PTT Driver: none

Channel Access:
TxDelay: 150
Slot Time: 100
P-Persistence: 40
Full Duplex: not selected
TxTail: 10

Channel 0:
Modulator:
Mode: afsk
Bits/s: 1200
Freq 0: 1200
Freq 1: 2200
Differential: selected

Demodulator:
Mode: afsk
Bits/s: 1200
Freq 0: 1200
Freq 1: 2200
Differential: selected

Packet IO:
Mode: MKISS
Interface: sm0
Callsign: mycall
IP address: 10.0.0.1
Network mask: 255.255.255.0
Broadcast addr: 10.0.0.255

I also set up /etc/ax25/axports to have:

sm0 mycall 1200 255 7 144.39 APRS (1200 bps)

Finally, I made sure Avahi was set to ignore sm0. This is easier than it was prevously – now you just add:

deny-interfaces=sm0

to /etc/avahi/avahi-daemon.conf

Once that’s done, don’t forget to chmod 4755 /usr/bin/xastir so it can open sm0 and things are good.


Speed up those boring meeting replays with mplayer

December 29, 2010

It’s been a while since I looked at the man page for mplayer. Ubuntu has finally included something I’ve wanted for a long time.

Every now and then I have to listen to pre-recorded meetings. Since I usually think faster than the speakers can talk (“umm, uhh… could you go to the next slide please?”) I like to speed things up.

I used to have to use sox to change the playback speed without changing the pitch, but now it appears it’s built into mplayer, which makes it much easier.

Here’s how to do it:

mplayer -af scaletempo -speed 1.3 boringmeeting.mp3

This plays back at 1.3 times the usual speed, which is good for most speakers. Really slow ones will benefit from -speed 1.5.

When I was young, I had an LP with the song “Twilight Zone” by Golden Earring on it. I used to listen to that at 45 rpm instead of 33 rpm because it made it sound more urgent. That would be -speed 1.363 if you’re playing at home.


Converting audio files under Linux

December 29, 2010

Linux has mplayer, an excellent audio player. It’s also handy when you want to convert a sound file from one format to another. The secret is to use .wav as an intermediate conversion, since most audio converters know how to handle that.

Here is the magic incantation for mplayer:

mplayer -quiet -vo null -vc dummy -ao pcm:waveheader:file="output.wav" input.rm

This takes the input file and creates output.wav from it. Once you have that, it’s a simple matter of

oggenc output.wav

to get output.ogg (don’t forget to install vorbis-tools) or

lame output.wav

if MP3s are your bag.

Linux Review has a good article on converting using this technique