Streaming Audio with Ices and Icecast

Retransmit from a radio scanner to the Internet via Ices and Icecast.
Fine-Tuning

Once I had everything set up and running, I spent a fair amount of time fine-tuning the audio. The first thing I found was that the audio level was quite low. Normally, when I want to turn up the audio level, I use KMix. But, I hadn't installed a window manager on my encoding computer. My system uses ALSA as the sound system, and I found out that there is a great curses-based mixer for ALSA named Alsamixer. It allows you to use the arrow keys to change settings. Figure 4 shows the settings I chose for my card. My final preference was to have the Master and PCM both at 100%. I also chose to mute everything else, because I knew they would not be in use.

Figure 4. Alsamixer Settings

Now that the audio was loud enough, I still had another problem. The audio sounded choppy. After looking around for a while, I realized that the processor usage was at 100%. I tried to reduce the bitrate by changing the value of the nominal-bitrate setting. With the bitrate set sufficiently low, the audio sounded good. I guess you can't encode very high-quality audio with a 233MHz processor.

When the audio sounded good, my goal was to lower the bitrate as much as possible while keeping an acceptable level of audio quality. In my case, an “acceptable level” is quite low. The traffic on the W0ZWY repeater is only voice, because it is illegal to transmit music in the amateur radio bands.

Three aspects of the encoded audio will affect its quality and bitrate: number of channels, sample rate and bitrate. I started by setting the downmix to 1, because the scanner is only mono. Then, I incrementally decreased the sample rate until I found the lowest setting that rendered acceptable audio; 11127Hz ended up being the minimum. Instead of setting the bitrate with the nominal-bitrate setting, I used the quality setting. The quality setting directly affects the final bitrate. With a few tries, I chose a quality level of 2.

With my final settings, the bitrate stays around 30Kbps, and the processor hovers around 40% usage.

Conclusion

There are probably many other applications where this type of system would be useful. Keep in mind, however, if you are interested in using this type of system for streaming music, make sure you have permission from the artists and recording studios.

This combination of open-source projects really worked well together. Setting up everything was quite simple. I spent most of my time tweaking the quality and sample rate settings. The traffic on my streamer is quite low. I usually have only one or two connections per week. But, it was fun to learn, and it is my little way of participating in the amateur radio community.

Brian Matherly is a Software Engineer at Sencore Electronics in Sioux Falls, South Dakota. He is also an adjunct professor at Colorado Technical University.

______________________

Comments

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Out of date

Paul Duncan's picture

Hi,

I suggest removal of this article. It seems that things have moved on so much, that all it does is waste people's time. I need to do *exactly* what this guy is doing, but I can't follow the procedure here as the software has changed significantly in two years.

Best Regards,

Paul
~~~~~

Webinar
One Click, Universal Protection: Implementing Centralized Security Policies on Linux Systems

As Linux continues to play an ever increasing role in corporate data centers and institutions, ensuring the integrity and protection of these systems must be a priority. With 60% of the world's websites and an increasing share of organization's mission-critical workloads running on Linux, failing to stop malware and other advanced threats on Linux can increasingly impact an organization's reputation and bottom line.

Learn More

Sponsored by Bit9

Webinar
Linux Backup and Recovery Webinar

Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.

In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.

Learn More

Sponsored by Storix